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At least 235 records · Page 13Linked to original sources

bioRxiv2016

Redox potential as a master variable controlling pathways of metal reduction by Geobacter sulfurreducens

Geobacter sulfurreducens uses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of -0.10 V vs. the Standard Hydrogen Electrode (SHE), while the ImcH-dependent pathway operates only above this value. Here, we provide evidence that G. sulfurreducens also requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)- (oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment.

Microbiology↗

bioRxiv2016

Wedding higher taxonomic ranks with metabolic signatures coded in prokaryotic genomes

Taxonomy of prokaryotes has remained a controversial discipline due to the extreme plasticity of microorganisms, causing inconsistencies between phenotypic and genotypic classifications. The genomics era has enhanced taxonomy but also opened new debates about the best practices for incorporating genomic data into polyphasic taxonomy protocols, which are fairly biased towards the identification of bacterial species. Here we use an extensive dataset of Archaea and Bacteria to prove that metabolic signatures coded in their genomes are informative traits that allow to accurately classify organisms coherently to higher taxonomic ranks, and to associate functional features with the definition of taxa. Our results support the ecological coherence of higher taxonomic ranks and reconciles taxonomy with traditional chemotaxonomic traits inferred from genomes. KARL, a simple and free tool useful for assisting polyphasic taxonomy or to perform functional prospections is also presented (https://github.com/giraola/KARL).

Microbiology↗

bioRxiv2016

Evaluation of SNP-based genotyping to monitor tuberculosis control in a high MDR-TB setting

Mycobacterium tuberculosis (Mtb) lineage identification and typing of clinical isolates in general is performed only retrospectively. The results are rarely linked to drug susceptibility testing (DST) or patient data. Consequently, the association between Mtb lineage, (multi)drug resistance and treatment history is not fully explored at the local level. Here we evaluated a new SNP based typing assay. We furthermore assessed the added value of genotyping of Mtb isolates for epidemiological purposes and guidance of tuberculosis (TB) control. Mtb lineage, DST profile and treatment history were determined for 399 samples at the National TB Reference Laboratory (NRL) in Tbilisi, Georgia by local staff. Data was shared electronically and analysis was performed remotely. Out of 399 isolates, 74 (74/399, 18.5%) were at least multidrug resistant (MDR)-TB, of which 63 (63/74, 85.1%) were members of three different Mtb Beijing lineages. Previous treatment was reported in 38/74 (51.4%) MDR(+) patients. The availability of this data allows associations with lineages. Notably, multidrug resistant TB was more strongly associated with the Beijing lineage than treatment history. Of all MDR-TB Beijing strains 56.7% (42/74) were members of a genetic cluster. This is most easily explained by (ongoing) MDR-TB transmission rather than drug resistance amplification. This knowledge is useful when designing intervention strategies for MDR-TB. Our study provides an example that on-site integrated Mtb genotyping is realistic and could support TB control activities.

Microbiology↗

bioRxiv2016

Genomic epidemiology and global diversity of the emerging bacterial pathogen Elizabethkingia anophelis

Elizabethkingia anophelis is an emerging pathogen. Genomic analysis of strains from clinical, environmental or mosquito sources is needed to understand the epidemiological emergence of E. anophelis and to uncover genetic elements implicated in antimicrobial resistance, pathogenesis, or niche adaptation. Here, the genomic sequences of two nosocomial isolates that caused neonatal meningitis in Bangui, Central African Republic, were determined and compared with Elizabethkingia isolates from other world regions and sources. Average nucleotide identity firmly confirmed that E. anophelis, E. meningoseptica and E. miricola represent distinct genomic species and led to re-identification of several strains. Phylogenetic analysis of E. anophelis strains revealed several sublineages and demonstrated a single evolutionary origin of African clinical isolates, which carry unique antimicrobial resistance genes acquired by horizontal transfer. The Elizabethkingia genus and the species E. anophelis had pan-genomes comprising respectively 7,801 and 6,880 gene families, underlining their genomic heterogeneity. African isolates were capsulated and carried a distinctive capsular polysaccharide synthesis cluster. A core-genome multilocus sequence typing scheme applicable to all Elizabethkingia isolates was developed, made publicly available (http://bigsdb.web.pasteur.fr/elizabethkingia), and shown to provide useful insights into E. anophelis epidemiology. Furthermore, a clustered regularly interspaced short palindromic repeats (CRISPR) locus was uncovered in E. meningoseptica, E. miricola and in a few E. anophelis strains. CRISPR spacer variation was observed between the African isolates, illustrating the value of CRISPR for strain subtyping. This work demonstrates the dynamic evolution of E. anophelis genomes and provides innovative tools for Elizabethkingia identification, population biology and epidemiology.\n\nIMPORTANCEElizabethkingia anophelis is a recently recognized bacterial species involved in human infections and outbreaks in distinct world regions. Using whole-genome sequencing, we showed that the species comprises several sublineages, which differ markedly in their genomic features associated with antibiotic resistance and host-pathogen interactions. Further, we have devised high-resolution strain subtyping strategies and provide an open genomic sequence analysis tool, facilitating the investigation of outbreaks and tracking of strains across time and space. We illustrate the power of these tools by showing that two African healthcare-associated meningitis cases observed 5 years apart were caused by the same strain, providing evidence that E. anophelis can persist in the hospital environment.

Microbiology↗

bioRxiv2016

Synthesis of titanium dioxide thin films and its application in reducing microbial load of milk

Milk has rich nutritional content packed with fats, proteins and water. It also contains beneficiary and non-beneficiary microbes which account for its short shelf life. Currently cold storage, pasteurization, ultra-high temperature, microfiltration and addition of lactose peroxidase are the methods of choice to control milk spoilage and prolong its shelf life. Their limitations include high energy consumption and loss of variable proportion of heat sensitive nutrients. Titanium dioxide (TiO2) nanoparticle coated thin film was used in food packaging industry for its antimicrobial property. TiO2 thin films were synthesized by sol gel process; it was characterized with scanning electron microscopy which showed pore size as 5 m and Fourier transform infrared spectroscopy which showed metal present in sample is TiO2, zinc and silver. Exposure of raw milk at room temperature to TiO2 thin films doped with zinc or copper for a couple of hours showed zone of inhibition in disc diffusion technique, reduction in acid production. It also showed reduction in optical density indicating inhibition of growth in growth curve analysis, increase in the time required for methylene blue reduction and a five log folds decrease in bacterial count estimated using serial dilution plate count. The present studies were carried out under room temperature and pressure which is an added advantage in terms of energy as well as retention of nutrients. Though TiO2 is insoluble in water one needs to address it toxicity issues and adverse effects if any on the nutritional quality of milk before scaling up the process.

Microbiology↗

bioRxiv2016

Isolation of infective Zika virus from urine and saliva of patients in Brazil

BACKGROUNDZika virus (ZIKV) is an emergent threat provoking a worldwide explosive outbreak. Since January 2015, 41 countries reported autochthonous cases. In Brazil, an increase in Guillain-Barre syndrome and microcephaly cases was linked to ZIKV infections. A recent report describing low experimental transmission efficiency of its main putative vector, Ae. aegypti, in conjunction with apparent sexual transmission notifications prompted the investigation of other potential sources of viral dissemination. Urine and saliva have been previously established as useful tools in ZIKV diagnosis. However, no evidence regarding the infectivity of ZIKV particles present in saliva and urine has been obtained yet.\n\nMETHODOLOGY/PRINCIPAL FINDINGSNine urine and five saliva samples from nine patients from Rio de Janeiro presenting rash and other typical Zika acute phase symptoms were inoculated in Vero cell culture and submitted to specific ZIKV RNA detection and quantification through, respectively, NAT-Zika, RT-PCR and RT-qPCR. Two ZIKV isolates were achieved, one from urine and one from saliva specimens. ZIKV nucleic acid was identified by all methods in four patients. Whenever both urine and saliva samples were available from the same patient, urine viral loads were higher, corroborating the general sense that it is a better source for ZIKV molecular diagnostic. In spite of this, from the two isolated strains, each from one patient, only one derived from urine, suggesting that other factors, like the acidic nature of this fluid, might interfere with virion infectivity. The complete genome of both ZIKV isolates was obtained. Phylogenetic analysis revealed similarity with strains previously isolated during the South America outbreak.\n\nCONCLUSIONS/SIGNIFICANCEThe detection of infectious ZIKV particles in urine and saliva of patients during the acute phase may represent a critical factor in the spread of virus. The epidemiological relevance of this finding, regarding the contribution of alternative non vectorial ZIKV transmission routes, needs further investigation.\n\nAUTHOR SUMMARYThe American continent has recently been the scene of a devastating epidemic of Zika virus and its severe manifestations, such as microcephaly in newborns and Guillain-Barre Syndrome. Zika virus, first detected in 1947 in Africa, only from 2007 started provoking outbreaks. Zika, dengue and chikungunya viruses are primarily transmitted by Aedes mosquitoes. Dengue is endemic in Brazil for almost 30 years, and the country is largely infested by its main vector, Aedes aegypti. Chikungunya virus entered the country in late 2014 and Zika presence was confirmed eight months later. Nevertheless, Zika notifications multiplied and spread across the country with unprecedented speed, raising the possibility of other transmission routes. This hypothesis was strengthened by some recent reports of Zika sexual transmission in Ae. aegypti-free areas and by the description of a low transmission efficiency to Zika virus in local Ae. aegypti. We found Zika active particles in both urine and saliva of acute phase patients, and a finding that was promptly announced by Fiocruz via Press Conference on February 5, 2016. In this work, we bring up the potential alternative person-to-person infection routes beyond the vectorial transmission, that might have epidemiological relevance.

Microbiology↗

bioRxiv2016

Absence of Genome Reduction In Diverse, Facultative Endohyphal Bacteria

Fungi interact closely with bacteria both on the surfaces of hyphae, and within their living tissues (i.e., endohyphal bacteria, EHB). These EHB can be obligate or facultative symbionts, and can mediate a diverse phenotypic traits in their hosts. Although EHB have been observed in many major lineages of fungi, it remains unclear how widespread and general these associations are, and whether there are unifying ecological and genomic features found across all EHB strains. We cultured 11 bacterial strains after they emerged from the hyphae of diverse Ascomycota that were isolated as foliar endophytes of cupressaceous trees, and generated nearly complete genome sequences for all. Unlike the genomes of largely obligate EHB, genomes of these facultative EHB resemble those of closely related strains isolated from environmental sources. Although all analyzed genomes encode structures that can be used to interact with eukaryotic hosts, we find no known pathways that facilitate intimate EHB-fungal interactions in all strains. We isolated two strains with nearly identical genomes from different classes of fungi, consistent with previous suggestions of horizontal transfer of EHB across endophytic hosts. Because bacteria are differentially present during the fungal life cycle, these genomes could shed light on the mechanisms of plant growth promotion by fungal endophytes during the symbiotic phase as well as degradation of plant material during saprotrophic and reproductive phases. Given the capacity of EHB to influence fungal phenotypes, these findings illuminate a new dimension of fungal biodiversity.

Microbiology↗

bioRxiv2016

Wolbachia confers sex-specific resistance and tolerance to enteric but not systemic bacterial infection in Drosophila

Wolbachia-mediatedprotection against viral infection has been extensively demonstrated in Drosophila and in mosquitoes that are artificially inoculatedwith D. melanogaster Wolbachia (wMel), but to date no evidence for Wolbachia-mediated antibacterial protection has been demonstrated in Drosophila.Here we show that D. melanogaster carrying wMel shows reduced mortality during enteric - but not systemic - infection with the opportunist pathogen Pseudomonas aeruginosa, and that protection is more pronounced in male flies. Wolbachia-mediated protection is associated with increased early expression of the antimicrobial peptide attacinA, followed by increased expression of a ROS detoxification gene (gstD8), and other tissue damage repair genes which together contribute to greater host resistance and disease tolerance. These results highlight that the route of infection is important for symbiont-mediated protection from infection, that Wolbachia can protect hosts by eliciting a combination of resistance and disease tolerance mechanisms, and that these effects are sexually dimorphic.

Microbiology↗

bioRxiv2016

Classification of Wolbachia (Alphaproteobacteria, Rickettsiales): No evidence for a distinct supergroup in cave spiders

To the editor To the editor References Wolbachia are intracellular, inherited Alphaproteobacteria present in a large proportion of arthropod species and in filarial nematodes. Wolbachia-host interactions are many-faceted and include, but are not limited to reproductive manipulations (Werren et al. 2008), nutritional mutualism (Nikoh et al. 2014), and protection from pathogens (Hedges et al. 2008, Teixeira et al. 2008). Although there is just a single Wolbachia species described, the genus is highly diverse with regard to its distribution, phenotypes induced in the host, and genomic architecture. The generally accepted classification scheme currently in use differentiates among genetically distinct, monophyletic lineages named \"supergroups\" (Lindsey et al. 2016). To date, 16 of th ...

Microbiology↗

bioRxiv2016

The Impact of African and Brazilian Zika virus isolates on neuroprogenitors

In the last few months, an overwhelming number of people have been exposed to the Zika virus (ZIKV) in South and Central America. Here we showed, in vitro, that a Brazilian isolate impacts more severely murine neuronal progenitors and neurons than the African strain MR766. We found that the Brazilian isolate more pronouncedly inhibits neurite extension from neurospheres, alters their differentiation potential and causes neurons to have less and shorter processes. Comparing both lineages using a panel of inflammatory cytokines, we showed, with human neuroblastoma cells, that ZIKV induces the production of several inflammatory and chemotactic cytokines and once again, the Brazilian isolate had a more significant impact. Although much more needs to be studied regarding the association of ZIKV infection and brain damage during development, our study sheds some light into the differences between African and American lineages and the mechanisms by which the virus may be affecting neurogenesis.

Microbiology↗

bioRxiv2016

Isolation and characterization of electrochemically active subsurface Delftia and Azonexus species

Continental subsurface environments can present significant energetic challenges to the resident microorganisms. While these environments are geologically diverse, potentially allowing energy harvesting by microorganisms that catalyze redox reactions, many of the abundant electron donors and acceptors are insoluble and therefore not directly bioavailable. Extracellular electron transfer (EET) is a metabolic strategy that microorganisms can deploy to meet the challenges of interacting with redox-active surfaces. Though mechanistically characterized in a few metal-reducing bacteria, the role, extent, and diversity of EET in subsurface ecosystems remains unclear. Since this process can be mimicked on electrode surfaces, it opens the door to electrochemical techniques to enrich for and quantify the activities of environmental microorganisms in situ. Here, we report the electrochemical enrichment of microorganisms from a deep fractured-rock aquifer in Death Valley, California, USA. In experiments performed in mesocosms containing a synthetic medium based on aquifer chemistry, four working electrodes were poised at different redox potentials (272, 373, 472, 572 mV vs. SHE) to serve as electron acceptors, resulting in anodic currents coupled to the oxidation of acetate during enrichment. The anodes were dominated by Betaproteobacteria from the families Comamonadaceae and Rhodocyclaceae. A representative of each dominant family was subsequently isolated from electrode-associated biomass. The EET abilities of the isolated Delftia strain (designated WE1-13) and Azonexus strain (designated WE2-4) were confirmed in electrochemical reactors using working electrodes poised at 522 mV vs. SHE. The rise in anodic current upon inoculation was correlated with a modest increase in total protein content. Both genera have been previously observed in mixed communities of microbial fuel cell enrichments, but this is the first direct measurement of their electrochemical activity. While alternate metabolisms (e.g. nitrate reduction) by these organisms were previously known, our observations suggest that additional hidden interactions with external electron acceptors are also possible. Electrochemical approaches are well positioned to dissect such extracellular interactions that may be prevalent in the subsurface.

Microbiology↗

bioRxiv2016

Functional metagenomics reveals novel β-galactosidases not predictable from gene sequences

A soil metagenomic library carried in pJC8 (an IncP cosmid) was used for functional complementation for {beta}-galactosidase activity in both -Proteobacteria (Sinorhizobium meliloti) and{gamma} -Proteobacteria (Escherichia coli). One {beta}-galactosidase, encoded by overlapping clones selected in both hosts, was identified as a member of glycoside hydrolase family 2. ORFs obviously encoding possible {beta}-galactosidases were not identified in 19 other clones that were only able to complement S. meliloti. Based on low sequence similarity to known glycoside hydrolases but not {beta}-galactosidases, three ORFs were examined further. Biochemical analysis confirmed that all encoded {beta}-galactosidase activity. Bioinformatic and structural modeling implied that Lac161_ORF10 protein represented a novel enzyme family with a five-bladed propeller glycoside hydrolase domain.

Microbiology↗

bioRxiv2016

Characterization of sterol synthesis in bacteria

Sterols are essential components of eukaryotic cells whose biosynthesis and function in eukaryotes has been studied extensively. Sterols are also recognized as the diagenetic precursors of steranes preserved in sedimentary rocks where they can function as geological proxies for eukaryotic organisms and/or aerobic metabolisms and environments. However, production of these lipids is not restricted to the eukaryotic domain as a few bacterial species also synthesize sterols. Phylogenomic studies have identified genes encoding homologs of sterol biosynthesis proteins in the genomes of several additional species, indicating that sterol production may be more widespread in the bacterial domain than previously thought. Although the occurrence of sterol synthesis genes in a genome indicates the potential for sterol production, it provides neither conclusive evidence of sterol synthesis nor information about the composition and abundance of basic and modified sterols that are actually being produced. Here, we coupled bioinformatics with lipid analyses to investigate the scope of bacterial sterol production. We identified oxidosqualene cyclase (Osc), which catalyzes the initial cyclization of oxidosqualene to the basic sterol structure, in 34 bacterial genomes from 5 phyla (Bacteroidetes, Cyanobacteria, Planctomycetes, Proteobacteria and Verrucomicrobia) and in 176 metagenomes. Our data indicate that bacterial sterol synthesis likely occurs in diverse organisms and environments and also provides evidence that there are as yet uncultured groups of bacterial sterol producers. Phylogenetic analysis of bacterial and eukaryotic Osc sequences revealed two potential lineages of the sterol pathway in bacteria indicating a complex evolutionary history of sterol synthesis in this domain. We characterized the lipids produced by Osc-containing bacteria and found that we could generally predict the ability to synthesize sterols. However, predicting the final modified sterol based on our current knowledge of bacterial sterol synthesis was difficult. Some bacteria produced demethylated and saturated sterol products even though they lacked homologs of the eukaryotic proteins required for these modifications emphasizing that several aspects of bacterial sterol synthesis are still completely unknown. It is possible that bacteria have evolved distinct proteins for catalyzing sterol modifications and this could have significant implications for our understanding of the evolutionary history of this ancient biosynthetic pathway.

Microbiology↗

bioRxiv2016

Growth-Environment Dependent Modulation of Staphylococcus aureus Branched-Chain to Straight-Chain Fatty Acid Ratio and Incorporation of Unsaturated Fatty Acids

The fatty acid composition of membrane glycerolipids is a major determinant of Staphylococcus aureus membrane biophysical properties that impacts key factors in cell physiology including susceptibility to membrane active antimicrobials, pathogenesis, and response to environmental stress. The fatty acids of S. aureus are considered to be a mixture of branched-chain fatty acids (BCFAs), which increase membrane fluidity, and straight-chain fatty acids (SCFAs) that decrease it. The balance of BCFAs and SCFAs in strains USA300 and SH1000 was affected considerably by differences in the conventional laboratory medium in which the strains were grown with media such as Mueller-Hinton broth and Luria broth resulting in high BCFAs and low SCFAs, whereas growth in Tryptic Soy Broth and Brain-Heart Infusion broth led to reduction in BCFAs and an increase in SCFAs. Straight-chain unsaturated fatty acids (SCUFAs) were not detected. However, when the organism was grown ex vivo in serum, the fatty acid composition was radically different with SCUFAs, which increase membrane fluidity, making up a substantial proportion of the total (<25%) with SCFAs (>37%) and BCFAs (>36%) making up the rest. Staphyloxanthin, an additional major membrane lipid component unique to S. aureus, tended to be greater in content in cells with high BCFAs or SCUFAs. Cells with high staphyloxanthin content had a lower membrane fluidity that was attributed to increased production of staphyloxanthin. S. aureus saves energy and carbon by utilizing host fatty acids for part of its total fatty acids when growing in serum. The fatty acid composition of in vitro grown S. aureus is likely to be a poor reflection of the fatty acid composition and biophysical properties of the membrane when the organism is growing in an infection in view of the role of SCUFAs in staphylococcal membrane composition and virulence.\n\nFundingThis work was funded in part by grant 1R15AI099977 to Brian Wilkinson and Craig Gatto and grant 1R15GM61583 to Craig Gatto from the National Institutes of Health

Microbiology↗

bioRxiv2016

Isolation and Genomic Characterization of Desulfuromonas soudanensis WTL, a Metal- and Electrode-Reducing Bacterium from Anoxic Deep Subsurface Brine

Reaching a depth of 713 m below the surface, the Soudan Underground Iron Mine (Soudan, Minnesota, USA) transects a massive Archaean (2.7 Ga) banded iron formation, providing a remarkably accessible window into the terrestrial deep biosphere. Despite carbon limitation, metal-reducing microbial communities are present in potentially ancient anoxic brines continuously emanating from exploratory boreholes on Level 27. Using graphite electrodes deposited in situ as bait, we enriched and isolated a novel halophilic iron-reducing Deltaproteobacterium, Desul-furomonas soudanensis strain WTL, from an acetate-fed three-electrode bioreactor poised at +0.24 V (vs. standard hydrogen electrode). Cyclic voltammetry revealed that D. soudanensis releases electrons at redox potentials approximately 100 mV more positive than the model freshwater surface isolate Geobacter sulfurreducens, suggesting that its extracellular respiration is tuned for higher potential electron acceptors. D. soudanensis contains a 3,958,620-bp circular genome, assembled to completion using single-molecule real-time (SMRT) sequencing reads, which encodes a complete TCA cycle, 38 putative multiheme c-type cytochromes, one of which contains 69 heme-binding motifs, and a LuxI/LuxR quorum sensing cassette that produces an unidentified N-acyl homoserine lactone. Another cytochrome is predicted to lie within a putative prophage, suggesting that horizontal transfer of respiratory proteins plays a role in respiratory flexibility among metal reducers. Isolation of D. soudanensis underscores the utility of electrode-based approaches for enriching rare metal reducers from a wide range of habitats.

Microbiology↗

bioRxiv2016

Accurate measurement of the effects of all amino-acid mutations to influenza hemagglutinin

Influenza genes evolve mostly via point mutations, and so knowing the effect of every amino-acid mutation provides information about evolutionary paths available to the virus. We previously used high-throughput mutagenesis and deep sequencing to estimate the effects of all mutations to an H1 influenza hemagglutinin on viral replication in cell culture (Thyagarajan and Bloom, 2014); however, these measurements suffered from sub-stantial noise. Here we describe advances that greatly improve the accuracy and reproducibility of our measurements. The largest improvements come from using a helper virus to reduce bottlenecks when generating viruses from plasmids. Our measurements confirm that antigenic sites on the globular head of hemagglutinin are highly tolerant of mutations. However, other regions - including stalk epitopes targeted by broadly neutralizing antibodies - have a limited capacity to evolve. The ability to accurately measure the effects of all influenza mutations should enhance efforts to understand and predict viral evolution.

Microbiology↗

bioRxiv2016

Evidence and role for bacterial mucin degradation in cystic fibrosis airway disease

Chronic respiratory infections are composed of complex microbial communities that incite persistent inflammation and airway damage. Despite the high density of bacteria that colonize the airways, nutrient sources that sustain bacterial growth in vivo are unknown. Here we examine the role of respiratory mucins in the ecological dynamics of the cystic fibrosis lung microbiota. While P. aeruginosa was unable to efficiently utilize mucins, saliva-derived anaerobes stimulated the growth of opportunistic pathogens when provided mucins as the sole carbon source. The fermentative metabolisms of these oral anaerobes generated amino acids and short chain fatty acids (propionate and acetate) during mucin enrichment in vitro, which were also found within expectorated sputum from CF patients. The significance of these findings was supported by in vivo P. aeruginosa gene expression, which revealed a heightened response to propionate. Given that propionate is exclusively derived from bacterial fermentation, these data support a central role for mucin fermentation in the carbon flux of the lower airways. More specifically, commensal oral bacteria may contribute to airway disease by degrading mucins, in turn providing nutrients for pathogens otherwise unable to obtain carbon in the lung.

Microbiology↗

bioRxiv2016

Discovery of a Natural Microsporidian Pathogen with a Broad Tissue Tropism in Caenorhabditis elegans

Microbial pathogens often establish infection within particular niches of their host for replication. Determining how infection occurs preferentially in specific host tissues is a key aspect of understanding host-microbe interactions. Here, we describe the discovery of a natural microsporidian parasite of the nematode Caenorhabditis elegans that has a unique tissue tropism compared to other parasites of C. elegans. We characterize the life cycle of this new species, Nematocida displodere, including pathogen entry, intracellular replication, and exit. N. displodere can invade multiple host tissues, including the epidermis, muscle, neurons, and intestine of C. elegans. Despite robust invasion of the intestine very little replication occurs there, with the majority of replication occurring in the muscle and epidermis. This feature distinguishes N. displodere from two closely related microsporidian pathogens, N. parisii and N. sp. 1, which exclusively invade and replicate in the intestine. Comparison of the N. displodere genome with N. parisii and N. sp. 1 reveals that N. displodere is the earliest diverging species of the Nematocida genus and devotes over 10% of its genome to a single species-specific gene family that may be mediating host interactions upon infection. Altogether, this system provides a convenient whole-animal model to investigate factors responsible for pathogen growth in different tissue niches.

Microbiology↗