Biology subjects

Nielsen, T. K.

Publications and source records attributed to Nielsen, T. K..

At least 19 recordsLinked to original sources

bioRxiv2026

Mechanism-guided Discovery of Fluoroacetate Dehalogenase (FAcD) Variants for Enzymatic PFAS Defluorination

Per- and polyfluoroalkyl substances (PFAS) are persistent anthropogenic "forever chemicals" whose strong C-F bonds (~460-533 kJ mol-1) resist defluorination, and the recast EU Drinking Water Directive sets parametric values of 0.10 ug L-1 for the sum of 20 specified PFAS and 0.50 ug L-1 for total PFAS. Here, we present DeFluorX, a mechanism-first pipeline that uses Boltz-2 to co-fold 2,150 bacterial fluoroacetate dehalogenase (FAcD) variants with 26 PFAS and fluoroacetate, generating uniformly high model confidence (rho = +0.08) but poorly tracked catalytic competence. Thus, the complexes were ranked and tiered by SN2-defluorination geometry based on the known mechanism of control of FAcDs RPA1163 with fluoroacetate: Odelta...C-alpha distance and Odelta-C-alpha-F angle; relay; carboxylate clamp; F-stabiliser; F-cradle; and penalties for scissile bond strength, backside occlusion, beta-fluorination and bond multiplicity. The tiering identified eight complexes (med angle 173.2 degrees, distance 2.91 A) with a high probability of degradation, including Alphaproteobacterial enzymes, with mono-, di- and trifluoroacetate attacking at 172-178 degrees versus 163 degrees for the control. We performed WaterMap, restrained 1 us Desmond MD, MM-GBSA and scans of the three WaterMap-aware best MD frames per complex using B3LYP/6-31G** QM/MM. All 12 frames exhibited product-end C-F cleavage with barriers ranging from 1.1 to 11.8 kcal mol-1, and the departing fluoride carried -0.43 to -0.63 e. The Laboratory validation is ongoing.

bioinformatics↗

bioRxiv2026

Preoperative thymic output and T cell repertoire diversity are associated with recurrence after nephrectomy for localized renal cell carcinoma

Radiographic thymic health and peripheral T-cell repertoire features have been linked to outcomes in renal cell carcinoma (RCC), but their prognostic value after curative-intent surgery is unclear. We quantified preoperative blood signal-joint T-cell receptor excision circles (sjTRECs), a marker of thymic output, in 218 patients with localized RCC undergoing nephrectomy and characterized T-cell receptor {beta} (TCR{beta}) repertoires in 201 patients. We assessed overall survival (OS) and recurrence-free survival (RFS) using Kaplan-Meier and Cox models adjusted for age, sex, and Leibovich risk group. High sjTREC levels were associated with longer RFS after adjustment for age, sex, and Leibovich risk group (hazard ratio [HR] 0.50; 95% confidence interval [CI], 0.29-0.87; p=0.015), with a concordant OS estimate (HR 0.62; 95% CI, 0.38-1.02; p=0.058). sjTREC provided additional prognostic information beyond Leibovich risk stratification for recurrence overall and among intermediate/high-risk patients (likelihood-ratio test, p=0.024 and p=0.034, respectively). Higher TCR{beta} diversity was associated with longer RFS overall (HR 0.76; 95% CI, 0.60-0.96; p=0.024) and among intermediate/high-risk patients with longer RFS (HR 0.71; 95% CI, 0.55-0.92; p=0.009) and OS (HR 0.80; 95% CI, 0.65-0.98; p=0.031). Preoperative sjTREC provided prognostic information beyond clinicopathological risk, with higher TCR{beta} diversity associated with favorable outcomes.

cancer biology↗

bioRxiv2026

TFA-defluorinating microbial consortium achieved with analogue enrichment

Trifluoroacetate (TFA) is an ultra-short chain perfluoroalkyl substance (PFAS) and a pollutant of global significance; it is persistent and ubiquitous in the environment across compartments, including food, drinking water, animals, and humans. Concentrations in the environment are rising, concerns over the toxicity of the compound are increasing, and there are currently no efficient ways to remediate TFA pollution, as conventional methods are ineffective at scale under environmental conditions. Microorganisms possessing dehalogenating enzymes targeting the structurally analogous compound monofluoroacetate (MFA) present a potential solution to degrade TFA microbiologically. Due to previously demonstrated dehalogenation of difluoroacetate (DFA) by dehalogenases, the promiscuity of such enzymes was hypothesized to be extendable to TFA as well. In this study cultures obtained from an environmental sample of PFAS contaminated wastewater sludge were incubated in M9 minimal media supplied with 33 mM acetate and either 33 mM TFA, DFA, or MFA in an iterative manner, followed by testing in a 30-day experiment. Free fluoride (F-) was measured at 5 timepoints using a fluoride ion specific electrode (ISE). One culture designated MFA1C significantly degraded MFA, DFA, and TFA (two-way ANOVA mixed model, p < 0.05). MFA1C released 11.2 {+/-} 0.7 M F- which constitutes approximately 0.01% of the potential fluoride release from the total 33 mM TFA applied and with the greatest defluorination activity in the first 9 days of incubation. Fluoride release from TFA and formation of DFA and MFA was confirmed with 19F-NMR. Genetic sequencing and protein-ligand modelling identified two candidate dehalogenase enzymes from Achromobacter denitrificans and Stenotrophomonas sp., respectively, with potential capacity to degrade TFA. The findings of this study are a crucial first step towards future potential bioremediation of TFA, and are, to the best of our knowledge, the first to identify a TFA-degrading consortium of microorganisms.

microbiology↗

bioRxiv2026

Danish profile of soft rot Pectobacteriaceae; A three-year field sampling study proving several clonal clades of soft rot isolates across diverse locations implicating a common origin

Soft rot Pectobacteriaceae (SRP) are among the most economically important plant pathogenic bacteria and are especially known to be problematic in potato production. The epidemiology of disease transmission has been investigated for almost a century, and several aspects have been highlighted as plausible infection routes. However, it is generally accepted that the major source of disease is the latently infected mother tuber, but several parameters are still influencing disease prevalence including contaminated equipment, soil water status as well as temperature. Management of the disease is limited to hygiene practices, dry storage and seed certification systems but several studies have also proven biocontrol agents such as bacteriophages (phages) as promising tools. Despite the severity of SRP on potato production, little is known about the genetic diversity of SRPs in Denmark, and since only few isolates are available, the possibility to design a broadly effective phage cocktail is limited. Here we describe a three-year field study utilizing an agri-citizen science approach where Danish farmers provided symptomatic potato plants or tubers, together with metadata such as date, location, potato variety and origin. By using whole genome sequencing (Illumina and Nanopore) together with metadata we were able to investigate and monitor the epidemiological disease spread across the country using 103 complete genomes, sampled across all three years. In this study we provide epidemiological evidence of disease origins and a suite of phages that could be used as a biocontrol tool for early disease intervention. Our results revealed several clonal clades across diverse locations (SNPs < 20) which strongly indicate common origin. A total of 17 Pectobacterium phages were tested and did target > 80% of clonal clades. Based on the clonality across the soft rot isolates we propose the possibility to set in early on using phages targeting strains relevant for soft rot development, with the possibility of a surveillance program together with customizing the phage preference.

microbiology↗

bioRxiv2025

Genome compartmentalization in a host-specific fungal insect pathogen reveals a putative mating type locus on an accessory chromosome

The genomic diversity of many fungal pathogens is driven by rapidly evolving regions harbouring significant amounts of transposable elements. Such genomic regions often contain genes important for pathogenicity and may be sequestered from the core genome on accessory chromosomes, which are variably present in isolates of a species. In this study, we present a pangenomic analysis of a fungal insect pathogen, Metarhizium acridum, using seven chromosome-scale genomes from four different continents. We show that approximately 25% of the M. acridum pangenome is comprised of genes only present in one isolate (singletons) or more than one but not all isolates (accessory). These genes are enriched for functions in secondary metabolite production, nutrient transport, and chromosome organization. We also find evidence of functional compartmentalization of the genome, as the core genome of M. acridum is enriched in carbohydrate-active enzymes, while the accessory components are enriched in effectors that are located in gene-sparse regions of the genome. Furthermore, we identified the first naturally recovered accessory chromosome in M. acridum, which does not harbor effector or secondary metabolite proteins related to host-insect interactions but is enriched in functions related to sexual reproduction. Within the genus Metarhizium, M. acridum is one of few species considered to regularly reproduce sexually. We show that the accessory chromosome contains genes from both the MAT1-1 and MAT1-2 idiomorphs, in addition to the MAT locus found on the core chromosomes. Our findings suggest that the presence of this accessory chromosome may facilitate sexual reproduction, possibly even primary homothallism, in the otherwise heterothallic M. acridum. Overall, our study presents a putative novel mechanism whereby this fungal pathogen may acquire gene recombination and ensure maintenance of the accessory chromosome.

microbiology↗

bioRxiv2025

Identifying the Levant as a potential contact and interbreeding zone for Neanderthals and modern humans

Timing of interbreeding between modern humans and Neanderthals has been subject of numerous studies but its geography remains largely unknown. Genetic evidence suggests three different interbreeding events: first in the Marine Isotope Stage (MIS) 7 ([~]250 to 200 ka), then in the MIS5 ([~]100 to 120 ka) and the final event in the MIS3 ([~]60 to 50 ka). Here, we used all known archaeological sites between 60-50 ka associated with Neanderthals and modern human presence and a set of paleoenvironmental data to reconstruct Neanderthals and modern humans habitat suitability using the Species Distribution Modeling (SDM) techniques. Assessing geographical overlap between the two species, we identify potential interbreeding zone. We found that the Levant was main potential interbreeding area of the third event. Previous research has identified the Zagros Mountains in Iran as a potential interbreeding zone during the second interbreeding event MIS5 ([~]100 to 120 ka). Compiling the results of this study to previous research can help us to better understand the dynamics of modern humans and Neanderthals interbreeding over both time and space. The two potential interbreeding areas have high priority for future research.

evolutionary biology↗

bioRxiv2025

Mobilization of genes encoding potential PFAS-degradation enzymes and positive selection in cyanobacteria

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants due to their strong carbon-fluorine bonds and the toxicity of released fluoride from degradation, posing significant challenges for bioremediation. While microbial defluorination of PFAS has been described, the enzymatic mechanisms and evolutionary selection driving this capability is poorly understood. In this study, we screened all complete bacterial genomes in the NCBI RefSeq database for homologs of 43 candidate defluorinating enzymes, focusing on their genetic context and association with mobile genetic elements. Our analysis revealed that fluoroacetate dehalogenases and haloacid dehalogenases are among the most frequently mobilized enzyme classes, suggesting positive selection. Notably, a conserved gene encoding a fluoroacetate dehalogenase homolog in Microcystis cyanobacteria is consistently flanked by genes related to stress response, photosynthesis, and toxin-antitoxin systems, suggesting a potential adaption to alleviate PFAS toxicity. We propose that positive selection for PFAS degradation may be driven by mitigation of physiological stress rather than metabolic gain. These findings highlight the importance of considering ecological and genetic contexts in the search for effective PFAS-degrading microorganisms. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/666183v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@9a97f4org.highwire.dtl.DTLVardef@16e3969org.highwire.dtl.DTLVardef@17b2b97org.highwire.dtl.DTLVardef@16adedb_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Temperature-dependent regulation of bacterial cell division hydrolases by the coordinated action of a regulatory RNA and the ClpXP protease

A defining feature of bacteria is the peptidoglycan cell wall which provides structural integrity and prevents osmotic lysis. While peptidoglycan hydrolases are required for daughter cell separation, dysregulated cell wall degradation may result in cell lysis. The mechanisms allowing bacteria to control these deadly enzymes in response to environmental changes remain incompletely understood. Here, we find that in Staphylococcus aureus, temperature-dependent regulation of such hydrolases occurs by the coordinated action of a CHAP domain-specific regulatory RNA and the ClpXP protease. Using a proteomics approach, we identify a hitherto uncharacterized ClpXP controlled autolysin, CxcA, with a catalytic CHAP domain and show that it contributes to separation of daughter cells. CxcA is positively controlled by a non-coding RNA, named Rbc1 (for RNA binding to CHAP domain) transcribed from the antisense strand of cxcA. Notably, Rbc1 is capable of base pairing with RNAs encoding the CHAP domains of numerous cell wall hydrolases and we show that Rbc1 works in trans to upregulate the cell division hydrolase Sle1. Specifically, Rbc1 functions as a thermosensor allowing for upregulation of CxcA and Sle1 at low temperature where daughter cell separation is impeded. Interestingly, the Rbc1-mediated up-regulation of CxcA and Sle1 does not involve mRNA stabilization or increased translation; instead, Rbc1 depletion increases ClpXP-mediated degradation. In conclusion, we identify a novel cell division hydrolase that is highly conserved in Staphylococci and show that it is co-regulated with enzymes containing the catalytic CHAP domain via transcriptional regulation, an RNA-RNA temperature sensory mechanism and the ClpXP protease.

microbiology↗

bioRxiv2025

Exploring Clinical Class 1 Integrons as Valuable Targets for the Re-sensitization of Multidrug Resistant Pathogenic Bacteria Using CRISPR-Cas

The increasing prevalence of bacteria resistant to many or all types of antibiotics poses a major health crisis. Novel classes of antibiotics are only slowly being developed and alternative strategies are needed to tackle the issue. Mobile genetic elements and class 1 integrons are important facilitators for antibiotic resistance genes, with the latter being highly conserved in human pathogens. The growing prevalence of multidrug-resistant bacteria and the paucity in the development of new antibiotics underscore the urgent need for innovative approaches in the treatment of pathogens. Among these, CRISPR-Cas nucleases can be used to cleave acquired resistance genes, leading to either plasmid curing or cell death if the target is on a chromosome. In this study, we investigate the feasibility of using class 1 integrons as a target for Cas9-based cleavage leading to re-sensitizing antibiotic-resistant bacteria. We analyze the conserved and widespread integrase gene intI1 and conclude that it is a suitable target for Cas-based re-sensitization due to its high sequence conservation and its occurrence largely limited to human pathogens, alleviating the risk of targeting benign bacteria. We developed a broad host range conjugative plasmid encoding a class 1 integron-targeting Cas9 system that leads to removal of resistance plasmids in target bacteria with subsequent re-sensitization towards antibiotics. We find that 290 distinct ARGs co-occur on int1-harboring plasmids, showing the potential for re-sensitization towards a very broad range of antibiotics.

microbiology↗

bioRxiv2024

Single-strain mobilome sequencing quantifies bacterial genetic response to stress, including activity of IS elements, prophages, RNAs, and REPINs.

Microbial genomes are continuously being rearranged by mobile genetic elements (MGEs), leading to genetic configurations that may confer novel phenotypic traits such as antibiotic resistance, degradation of novel compounds, or other metabolic features. Standard genomic sequencing provides a snapshot of a genome in one configuration, but this static image does not give insight into the dynamics of genomic evolution and whether MGEs are actively changing a given genome. We applied single-strain mobilome sequencing to Escherichia coli K-12 substrain MG1655 under various stress conditions: UV, SDS, nalidixic acid, tetracycline, cetrimide, and copper. Under these conditions, we quantified the activity of a range of genetic elements, including extrachromosomal circular DNA (eccDNA) from IS elements, RNA genes, the UV-inducible e14 prophage, and intergenic repetitive sites (REP). Of the investigated stressors, copper and SDS are among the largest inducers of eccDNA formation from groups of IS elements, while elevated levels of hypothetical RNA/DNA heteroduplexes of ribosomal and transfer RNAs, and Rhs-nuclease proteins are induced under stress various stressors, especially copper and SDS. This approach holds promise for quantifying the genetic response to environmental stress and implications for genome plasticity. The observed mobilization of IS elements upon copper and other stressors helps to explain co-selection of heavy metals with antibiotic resistance genes and MGEs.

microbiology↗

bioRxiv2024

Pseudomonas taxonomic and functional microdiversity in the wheat rhizosphere is cultivar-dependent and links to disease resistance profile and root diameter

Diversity within lower taxonomic units in microbial communities is a key trait, giving rise to important ecological functions. In the rhizosphere, these functions include disease suppression and pathogen inhibition. However, limited effort has been given to exploring intragenus microdiversity in an increasingly homogenous agricultural system. Through an integrative approach combining culture-dependent and -independent methods, we explore the rhizosphere Pseudomonas pangenome and demonstrate cultivar-dependent taxonomic and functional microdiversity between two closely related modern winter wheat cultivars. A Fusarium-resistant cultivar demonstrated increased Pseudomonas taxonomic diversity but not biosynthetic diversity when compared to the susceptible cultivar, coinciding with a thinner root diameter of the resistant cultivar. We found enrichment of Pseudomonas isolates capable of antagonizing Fusarium as well as chitinase-encoding genes and pyoverdine gene clusters in the resistant cultivar. Across closely related Pseudomonas isolates from the two cultures, there were differences in genomic content and biosynthetic gene clusters. Ultimately, we highlight the need for fine-scale analysis to uncover the hidden microdiversity within rhizosphere Pseudomonas.

microbiology↗

bioRxiv2024

The Spx stress regulator confers high-level β-lactam resistance and decreases susceptibility to last-line antibiotics in methicillin resistant Staphylococcus aureus

Infections caused by methicillin resistant Staphylococcus aureus (MRSA) are a leading cause of mortality worldwide. MRSA have acquired resistance to next generation {beta}-lactam antibiotics through the horizontal acquisition of the mecA resistance gene. Development of high resistance is, however, often associated with additional mutations in a set of chromosomal core genes, known as potentiators which through poorly described mechanisms enhance resistance. The yjbH gene was recently identified as a hot spot for adaptive mutations during severe infections. Here, we show that inactivation of yjbH increased {beta}-lactam MICs up to 16-folds and transformed MRSA cells with low level of resistance to being homogenously highly resistant to {beta}-lactams. The yjbH gene encodes an adaptor protein that targets the transcriptional stress regulator Spx for degradation by the ClpXP protease. Using CRISPRi to knock down spx transcription, we unambiguously linked hyper-resistance to accumulation of Spx. Spx was previously proposed to be essential, however, our data indicate that Spx is dispensable for growth at 37{degrees}C but becomes essential in the presence of antibiotics with various targets. On the other hand, high Spx levels bypassed the role of PBP4 in {beta}-lactam resistance and broadly decreased MRSA susceptibility to compounds targeting the cell wall or the cell membrane including vancomycin, daptomycin, and nisin. Strikingly, Spx potentiated resistance independently of its redox sensing switch. Collectively, our study identifies a general stress pathway that, in addition to promoting the development of high-level, broad-spectrum {beta}-lactam resistance, also decreases MRSA susceptibility to critical antibiotics of last resort.

microbiology↗

bioRxiv2023

Activity and diversity of prophages harbored by wheat phyllosphere bacteria

1.The plant microbiome harbors an enormous diversity of fungi, bacteria, and viruses, but little is known on the diversity and function of prophages harbored within plant-associated bacteria. Using "VIP-Seq", a novel method based on supernatant sequencing, we identified and quantified the activity of 120 spontaneously induced prophages in a collection of 63 Erwinia and Pseudomonas strains isolated from wheat flag leaves collected from the same field. These bacterial strains exhibited high levels of spontaneous prophage induction, with some producing > 108 virions/mL in overnight culture. Significant induction in planta also occurred from a lysogenic Erwinia strain inoculated on wheat seedlings. The potential of these active prophages in bacterial warfare was exhibited by their widespread killing of rival bacterial strains. Evidence of transduction was observed, and the prophages were shown to contribute a majority of the non-core genome of E. aphidicola isolates. Many additional prophages were predicted by bioinformatic tools, and we found that the predicted prophages that were not spontaneously induced had a significantly higher number of IS elements. Our results suggest that spontaneous induction of prophages may represent an unknown but wide-spread competition mechanism involved in phyllosphere microbiome assembly and function. This may also have implications for the design and resilience of synthetic bacterial communities used as biocontrol for certain plant diseases.

microbiology↗

bioRxiv2021

Complete genome sequence and Benzophenone-3 mineralisation potential of Rhodococcus sp. USK10, a bacterium isolated from riverbank sediment.

Benzophenone-3 (BP3) is an organic UV filter whose presence in the aquatic environment has been linked to detrimental developmental impacts in aquatic organisms such as coral and fish. The genus Rhodococcus has been extensively studied and is known for possessing large genomes housing genes for biodegradation of a wide range of compounds, including aromatic carbons. Here, we present the genome sequence of Rhodococcus sp. USK10, which was isolated from Chinese riverbank sediment and is capable of utilising BP3 as the sole carbon source, resulting in full BP3 mineralisation. The genome consisted of 9,870,030 bp in 3 replicons, a G+C content of 67.2%, and 9,722 coding DNA sequences (CDSs). Annotation of the genome revealed that 179 of these CDSs are involved in metabolism of aromatic carbons. The complete genome of Rhodococcus sp. USK10 is the first complete, annotated genome sequence of a Benzophenone-3 degrading bacterium. Through radiolabelling, it is also the first bacterium proven to mineralise Benzophenone-3. Due to the widespread environmental prevalence of Benzophenone-3, coupled to its adverse impact on aquatic organisms, this characterisation provides an integral first step in better understanding the environmentally relevant degradation pathway of the commonly used UV filter. Given USK10s ability to completely mineralise Benzophenone-3, it could prove to be a suitable candidate for bioremediation application.

genomics↗

bioRxiv2021

Metaviromes reveal the dynamics of Pseudomonas host-specific phages cultured and uncultured by plaque assay

Isolating single phages using plaque assays is a laborious and time-consuming process. Whether single isolated phages are the most lyse-effective, the most abundant in viromes, or the ones with highest ability to plaque on solid media is not well known. With the increasing accessibility of high-throughput sequencing, metaviromics is often used to describe viruses in envi-ronmental samples. By extracting and sequencing metaviromes from organic waste with and without exposure to a host-of-interest, we show a host-related phage communitys shift, as well as identify the most enriched phages. Moreover, we isolated plaque-forming single phages using the same virome-host matrix to observe how enrichments in liquid media corresponds to the metaviromic data. In this study, we observed a significant shift (p = 0.015) of the 47 identified putative Pseudomonas phages with a minimum 2-fold change above 0 in read abundance when adding a Pseudomonas syringae DC3000 host. Surprisingly, it appears that only two out of five plaque-forming phages from the same organic waste sample, targeting the Pseudomonas strain, was highly abundant in the metavirome, while the other three were almost absent despite host exposure. Lastly, our sequencing results highlights how long reads from Oxford Nanopore elevates the assembly quality of metaviromes, compared to short reads alone.

microbiology↗

bioRxiv2021

Analyses of the complete genome sequence of 2,6-dichlorobenzamide (BAM) degrader Aminobacter sp. MSH1 suggests a polyploid chromosome, phylogenetic reassignment, and functions of (un)stable plasmids.

Aminobacter sp. MSH1 (CIP 110285) can use the pesticide dichlobenil and its transformation product, the recalcitrant groundwater micropollutant, 2,6-dichlorobenzamide (BAM) as sole source of carbon, nitrogen, and energy. The concentration of BAM in groundwater often exceeds the threshold limit for drinking water, resulting in the use of additional treatment in drinking water treatment plants (DWTPs) or closure of the affected abstraction wells. Biological treatment with MSH1 is considered a potential sustainable alternative to remediate BAM-contamination in drinking water production. Combining Illumina and Nanopore sequencing, we here present the complete genome of MSH1, which was determined independently in two different laboratories. Unexpectedly, divergences were observed between the two genomes, i.e. one of them lacked four plasmids compared to the other. Besides the circular chromosome and the two previously described plasmids involved in BAM catabolism pBAM1 (41 kb) and pBAM2 (54 kb), we observe that the genome of MSH1 contains two megaplasmids pUSP1 (367 kb) and pUSP2 (366 kb) and three smaller plasmids pUSP3 (97 kb), pUSP4 (64 kb), and pUSP5 (32 kb). The MSH1 substrain from KU Leuven showed a reduced genome lacking plasmids pUSP2 and the three smaller plasmids and was designated substrain MK1, whereas the variant with all plasmids was designated as substrain DK1. Results of a plasmid stability experiment, indicate that strain MSH1 may have a polyploid chromosome when growing in R2B medium with more chromosomes than plasmids per cell. Based on phylogenetic analyses, strain MSH1 is reassigned as Aminobacter niigataensis MSH1. ImportanceThe complete genomes of the two MSH1 substrains, DK1 and MK1, provide further insight into this already well-studied organism with bioremediation potential. The varying plasmid contents in the two substrains suggest that some of the plasmids are unstable, although this is not supported by the herein described plasmid stability experiment. Instead, results suggest that MSH1 is polyploid with respect to its chromosome, at least under some growth conditions. As the essential BAM-degradation genes are found on some of these plasmids, stable inheritance is essential for continuous removal of BAM. Finally, Aminobacter sp. MSH1 is reassigned as Aminobacter niigataensis MSH1, based on phylogenetic evidence.

microbiology↗

bioRxiv2021

Mobilization of antibiotic resistance genes differ by resistance mechanism

The degree to which antibiotic resistance genes (ARGs) are mobilized by insertion sequence (IS) elements, plasmids, and integrons has a strong association with their likelihood to function as resistance determinants. This stems from genetic decontextualization where strong promoters often present in IS elements and integrons and the copy number effect of plasmids contribute to high expression of accessory genes. Here, we screen all complete bacterial RefSeq genomes for ARGs. The genetic contexts of detected ARGs are investigated for IS elements, integrons, plasmids, and phylogenetic dispersion. The ARG-MOB scale is proposed which indicates how mobilized detected ARGs are in bacterial genomes. Antibiotic efflux genes are rarely mobilized and it is concluded that these are often housekeeping genes that are not decontextualized to confer resistance through overexpression. Even 80% of {beta}-lactamases have never, or very rarely, been mobilized in the 15,790 studied genomes. However, some ARGs are indeed mobilized and co-occur with IS elements, plasmids, and integrons. These results have consequences for the design and interpretation of studies screening for resistance determinants, as mobilized ARGs pose a more concrete risk to human health, especially under heterologous expression, than groups of ARGs that have only been shown to confer resistance in cloning experiments.

microbiology↗

bioRxiv2020

Potential Rhodopsin and Bacteriochlorophyll-Based Dual Phototrophy in a High Arctic Glacier

Conserving additional energy from sunlight through bacteriochlorophyll (BChl)-based reaction center or proton-pumping rhodopsin is a highly successful life strategy in environmental bacteria. Rhodopsin and BChl based systems display contrasting characteristics in the size of coding operon, cost of biosynthesis, ease of expression control, and efficiency of energy production. This raises an intriguing question of whether a single bacterium has evolved the ability to perform these two types of phototrophy complementarily according to energy needs and environmental conditions. Here we report four Tardiphaga sp. strains (Alphaproteobacteria) of monophyletic origin isolated from a high Arctic glacier in northeast Greenland (81.566{degrees} N, 16.363{degrees} W) that are at different evolutionary stages concerning phototrophy. Their >99.8% identical genomes contain footprints of horizontal operon transfers (HOT) of the complete gene clusters encoding BChl and xanthorhodopsin (XR)-based dual phototrophy. Two strains only possess a complete xanthorhodopsin (XR) operon, while the other two strains have both a photosynthesis gene cluster (PGC) and an XR operon in their genomes. All XR operons are heavily surrounded by mobile genetic elements and located close to a tRNA gene, strongly signaling that a HOT event of XR operon has occurred recently. Mining public genome databases and our High Arctic glacial and soil metagenomes revealed that phylogenetically diverse bacteria have the metabolic potential of performing BChl and rhodopsin-based dual phototrophy. Our data provide new insights on how bacteria cope with the harsh and energy-deficient environments in surface glaciers, possibly by maximizing the capability of exploiting solar energy. ImportanceOver billions of years of evolution, bacteria capable of light-driven energy production have occupied every corner of surface Earth where solar irradiation can reach. Only two general biological systems have evolved in bacteria to be capable of net energy conservation via light-harvesting: one is based on the pigment of (bacterio-)chlorophyll and the other based on light-sensing retinal molecules. There is emerging genomic evidence that these two rather different systems can co-exist in a single bacterium to take advantage of their contrasting characteristics in the number of genes involved, biosynthesis cost, ease of expression control and efficiency of energy production, and thus enhance the capability of exploiting solar energy. Our data provide the first clear-cut evidence that such dual phototrophy potentially exist in glacial bacteria. Further public genome mining suggests this understudied dual phototrophic mechanism is possibly more common than our data alone suggested. Sequence data availabilityGenomes, metagenomes and raw reads were deposited into GenBank under Bioprojects PRJNA548505 and PRJNA552582.

microbiology↗