Biology subjects

Patil, P. B.

Publications and source records attributed to Patil, P. B..

At least 19 recordsLinked to original sources

bioRxiv2026

Mutation in Ralstonia pseudosolanacearum F1C1 cytochrome p450 homologue impairs virulence through root but not through shoot of tomato plants

Ralstonia pseudosolanacearum causes a lethal bacterial wilt disease in many plants. The pathogen enters through roots and systemically colonizes the xylem tissue, resulting in wilting and eventual death of the host. Using transposon mutagenesis followed by screening in tomato seedlings, we identified a mutant exhibiting virulence deficiency by root inoculation, but not by leaf inoculation. The mutation was recreated in the wild-type genome via natural transformation to prove the linkage of virulence deficiency with the transposon insertion. Whole genome sequencing revealed that the transposon insertion was in a cyp450 homologue, encoding cytochrome P450 monooxygenase. Two independent targeted mutations were generated in the cyp450 gene, and both the mutants recapitulated the root-specific virulence deficiency. The mutants rarely cause disease in mature plants following soil drenching but remained fully virulent upon petiole pricking inoculation. Complementation with the full length cyp450 gene amplified from the wild-type strain F1C1 restored virulence in the mutant. Compared to the wild-type F1C1, the cyp450 mutants exhibited greater sensitivity to tomato root extracts. HR-LCMS of tomato root extracts revealed the occurrence of several antimicrobial compounds. Cytochrome P450 enzymes are known to mediate the degradation or biosynthesis of diverse metabolites in bacteria. Considering the virulence difference due to the mode of inoculation, our findings indicate that cyp450 contributes to tissue-specific adaptation of the pathogen during infection has opened an avenue for integrating tissue metabolomics with bacterial wilt susceptibility research.

pathology↗

bioRxiv2026

Xanthomonas pateli sp. nov. and X. hingoranii sp. nov. reveal a community of non-pathogenic Xanthomonas species complex in citrus

The genus Xanthomonas comprises a phylogenetically and ecologically diverse group of bacteria, historically characterized by economically important plant-pathogenic members affecting a wide range of agricultural crops. However, an increasing number of non-pathogenic and endophytic lineages have been recognized within the genus, expanding understanding of its taxonomic and ecological breadth. While it has been known for the last 30 years that non-pathogenic Xanthomonas (NPX) are present in diverse plants, studies from our lab over the last decade on the rice microbiome have revealed the presence of multiple, diverse NPX species as a community associated with a particular plant host. In this study, we identify two novel citrus plant-associated NPX species and provide evidence for the existence of an NPX community composed of multiple, diverse species, as in rice. Biochemical analysis, along with phylogenomic and genome-based taxonomic investigations, revealed that these strains represent two novel species within the genus Xanthomonas, providing evidence for a citrus-associated NPX community composed of multiple, diverse species, analogous to that described in rice. The lack of a canonical type III secretion system, along with multiple antimicrobial biosynthetic loci, as in the rice NPX community, points to their importance in plant microbiomes. Hence, such systematic studies of the NPX community need to be extended to all other plants. Accordingly, we propose that strain LMG 8992 (DSM =122509T) be classified as a novel species, Xanthomonas pateli sp. nov., and strain LMG 8993 (DSM = 122444T) be classified as a novel species, Xanthomonas hingoranii sp. nov.

microbiology↗

bioRxiv2026

Xanthomonas imtechensis sp. nov. - a novel member of non-pathogenic Xanthomonas with bioprotection function from healthy rice seeds

Non-pathogenic Xanthomonas (NPX) from a diverse plant hosts are being reported on an increasing basis. There are also reports of multiple species forming communities on a single host plant, such as rice, and, given their role as core endophytes in protecting plants from pathogens, it is essential to isolate and characterization of more NPX species from diverse host plants. Using phylogenomic analysis of publicly available Xanthomonas genome sequences, we identified a novel clade comprising NPX strains from diverse hosts. One of the strains previously reported from our lab is from healthy rice seeds and was reported to be non-pathogenic, with bio-protection function against the bacterial leaf blight pathogen. Genomic investigation confirmed the lack of type III secretion system and its effectors, consistent with their non-pathogenic nature. These strains also harbour core and unique biosynthetic loci identified in other non-pathogenic Xanthomonas (NPX) strains. Further investigation using multiple genomic-based taxonomic indices indicates that these strains represent a potential new species. Hence, we propose Xanthomonas imtechensis sp. nov. as a new species of the genus Xanthomonas, with the type strain being PPL568 = MTCC 13186 = CFBP 9040 = ICMP 24395.

microbiology↗

bioRxiv2025

Pseudomonas aeruginosa SPT08, a tomato endophyte, improves plant growth and controls bacterial wilt in tomato

Endophytes are a class of non-pathogenic microorganisms that reside within a plant and contribute to their health. Here, we isolated several endophytes from cotyledon-stage tomato seedlings that inhibited the growth of Ralstonia pseudosolanacearum, the bacterial wilt pathogen of tomato. One such endophyte, Pseudomonas aeruginosa SPT08, protected tomato seedlings as well as grown-up plants from the wilt disease. SPT08 also improved the tomato plant height by 20% and root growth by 60% in weight. SPT08 colonization inside tomato seedlings as well as in grown-up plants was studied using green fluorescent protein to demonstrate its endophytic behavior. SPT08 exhibited twitching and swimming motility and produced extracellular enzymes such as pectinase, protease, and amylase. SPT08 tested positive for several plant growth-promoting features such as phosphate solubilization, production of siderophore, plant hormone auxin, hydrogen cyanide, and ammonia. These features were further corroborated with SPT08 whole genome sequence. SPT08 genome is 6265489 bp, with 66.59% G+C and 5786 coding genes, including type II, III, and VI protein secretion systems. The antiSMASH tool identified potential for several secondary metabolites, including antibiotics, in SPT08. This study underscores the utility of P. aeruginosa SPT08 bio-protection from bacterial wilt and growth promotion agent in tomato. HighlightsPseudomonas aeruginosa SPT08, an endophyte isolated from tomato seedlings that inhibits bacterial wilt pathogen R. pseudosolanacearum, can control bacterial wilt in tomato plants and enhance the height and root growth.

plant biology↗

bioRxiv2024

Xanthomonas protegens sp. nov., a rice seed-associated probiotic and taxonomic outlier species of Xanthomonas sontii

Rice seed microbiota play a vital role throughout their growth and developmental stages. Xanthomonas sontii is known as an abundant, core-vertically transmitted rice seed endophyte with probiotic properties. Studies reveal a less explored world of non-pathogenic Xanthomonas (NPX) species like X. sontii and X. indica that are associated with healthy rice seeds. The present study reports the isolation, biochemical characterization, and in-depth taxonogenomic evidence for a third NPX species, X. protegens, from rice seeds, a taxonomic outlier of X. sontii. It also highlights the importance of using multiple taxonogenomic indices to identify taxonomic outlier species. Similar to the other two NPX species, the new member species is also non-pathogenic and provides in vivo protection to rice plants from Xanthomonas oryzae pv. oryzae upon leaf clip inoculation. The pangenome investigation suggested a set of unique genes to the novel species that might be important in adaptation to rice plants and differentiate it from other NPX species. The study will allow the design of markers for the identification of these NPX members, targeted culturomics of a particular NPX species and in the discovery of other novel NPX species from healthy rice seed microbiome for further exploitation in rice health.

evolutionary biology↗

bioRxiv2023

Xanthomonas sontii, and not Xanthomonas sacchari, is the dominant, vertically transmitted core rice seed endophyte

Seeds endophytes, particularly the abundant, core and vertically transmitted species, are major areas of focus in the host microbiome studies. Apart from being the first members to colonize, they accompany the plant throughout its development stages and also to the next generation. In a recently published study from china, a Xanthomonas species was reported as the keystone species that is core endophyte and vertically transmitted in rice with probiotic properties. However, the species status was wrongly reported as X. sacchari. Such report is misleading as Xanthomonas sacchari is a well-known and pathogenic species of sugarcane, and the study did not include the two-probiotic non-pathogenic Xanthomonas species from rice seeds, Xanthomonas sontii and Xanthomonas indica, that were discovered and investigated in details by our group, leading to the wrong inference. By including these species, we have correctly established the phylogenetic and taxonomic identity of keystone species as Xanthomonas sontii, a non-pathogen with plant protective functions. The course correction will enable researchers to use the correct reference or lab strain of X. sontii for further fundamental studies and translational research towards future agriculture.

microbiology↗

bioRxiv2023

Luteibacter sahnii sp. nov., a novel yellow-pigmented probiotic bacterium from rice seed microbiome.

The genus Luteibacter, a member of the family Rhodanobacteraceae, encompasses Gram-negative bacteria found in diverse environments. In the present study, four yellow-pigmented bacterial isolates designated as PPL193T, PPL201, PPL552, and PPL554 were obtained and identified as Gram-negative, rod-shaped, and motile bacteria. Biochemical characterization and examination of the 16S rRNA gene sequence, derived from the genomic sequence, identified it as belonging to the genus Luteibacter. The isolates are closely related to Luteibacter yeojuensis R2A16-10T, forming a distinct monophyletic lineage with L. aegosomatis KCTC 92392T and L. anthropi CCUG25036T. The calculated values for pairwise ortho Average Nucleotide Identity and digital DNA-DNA hybridization in comparison to previously reported Luteibacter species fell below the established thresholds for species delineation. As this novel species was isolated from rice seeds as a potential Xanthomonas due to its distinctive yellow-colored colonies, we sought to identify the presence of xanthomonadin pigment in this species. Intriguingly, our findings revealed the presence of the typical peak corresponding to xanthomonadin in the UV spectra, confirming its presence in this novel species and adaptation to plant habitat. Furthermore, the detailed genomic investigation also uncovered the genomic locus corresponding to xanthomonadin biosynthetic gene cluster, further suggesting that members of this novel species are co-habitants of plant pathogenic and plant probiotic Xanthomonas group of phytobacteria within rice seeds. Apart from protease production, the species was found to produce Indole-3-Acetic Acid (IAA) in higher quantities and was also able to protect plants from Xanthomonas oryzae pv. oryzae, a major pathogen of rice indicating its probiotic nature. Genome scanning revealed the presence of genomic region(s) encoding loci for biosynthesis of anti-microbial peptides and other metabolites with probiotic properties, further confirming its probiotic properties. This study highlights the importance of using a combination of phenotypic and genotypic methods for bacterial identification and expands our knowledge of the diversity and distribution of diverse bacteria associated with rice seeds and their microbiome. Luteibacter sahnii sp. nov. is proposed as a novel species of the genus Luteibacter with PPL193T=MTCC 13290T=ICMP 24807T=CFBP 9144T as its type strain and PPL201, PPL552, and PPL554 as other constituent members.

microbiology↗

bioRxiv2023

Phase variation in LPS O-antigen biosynthetic gene cluster of the rice pathogen Xanthomonas oryzaepv. oryzae

Bacteria respond to environmental cues in different ways. Phase variation is one such adaptation where heritable and reversible changes in DNA aid bacteria to alter the expression of specific genes. The bacterial plant pathogen Xanthomonas oryzae pv. oryzae (Xoo) causes the serious bacterial blight disease of rice. The mucoid phenotype of Xoo colonies is attributed to the secreted exopolysaccharide (EPS), xanthan gum. Spontaneous non-mucoid variants of Xoo which are deficient in EPS production and virulence were observed to accumulate in long-term stationary phase cultures. This phenomenon was termed stationary phase variation and variant colonies as stationary phase variants (SPV). Several but not all of these SPVs have been earlier described to carry spontaneous insertions of endogenous insertion sequence elements in the gum operon which encodes genes involved in EPS biosynthesis. In this study, we show that a number of SPVs harbour variations in the lipopolysaccharide (LPS) outer antigen (O-antigen) biosynthetic gene cluster. The data revealed that the vast majority of variations are due to either insertion of endogenous insertion sequence (IS) elements or slipped strand mispairing (SSM). Also, it was observed that many of these SPVs exhibited reversion to wild type mucoid phenotype via restoration of the wild type genotype. The results indicate that the phenomenon of phase variation is occurring in the LPS O-antigen biosynthetic gene cluster of Xoo.

microbiology↗

bioRxiv2023

Comparative genomics-based insights into diversification and bio-protection function of Xanthomonas indica, a non-pathogenic species of rice

Xanthomonas species have been extensively studied as major and model pathogens of plants. However, there is an increasing recognition of the complex and large world of non-pathogenic species of Xanthomonas in the recent decades. One pathogenic Xanthomonas species has been known in rice for the last hundred years, yet in recent years, three non-pathogenic Xanthomonas (NPX) species have been reported. Thus, there is a need to understand the species-level diversity of NPXs like their pathogenic counterparts. In the present study, we report isolation and investigation into the genomic diversity of Xanthomonas indica, a newly discovered NPX species from rice. The study allowed us to establish the relationship of X. indica strains within clade I of Xanthomonads. All the strains formed a distinct but diverse clade compared to clades corresponding to other NPX species from rice and other hosts. X. indica lacks major virulence factors found in their pathogenic counterparts. Identification of highly diverse strains and open-pan genome indicates ongoing selection to acquire new functions for adaptation. X. indica also harbours large-scale interstrain variations in the lipopolysaccharide O-antigen biosynthetic gene cluster, which hints at the selection at this locus. Interestingly, all the diverse strains of X. indica were able to protect rice from bacterial leaf blight pathogen of rice upon leaf clip inoculation. Comparative genomics revealed the association of a RiPP, a metalloprotease and a bacterial-killing type IV secretion system conserved across its related member species, including X. sontii, in the clade I with in-vivo anti-pathogenic properties. Overall the study has provided novel evolutionary insights into an important NPX member species. The findings and genomic resources will allow further systematic molecular studies to understand its interaction with the host plant.

genomics↗

bioRxiv2022

Deep phylotaxonogenomic revision of the genus Xanthomonas within family Xanthomonadaceae and proposal of novel family Frateuriaceae within order Xanthomonadales

Genus Xanthomonas is primarily comprise phytopathogenic species. In a recent study by carrying out deep phyto-taxonogenomics, we reported that even the genera Xylella, Stenotrophomonas and Pseudoxanthomonas are miss-classified and belong to genus Xanthomonas. Hence to understand the breadth of the genus, we carried out deep phylo-taxonogenomics of the order Xanthomonadales. Such investigation revealed that at least four more genera belong to genus Xanthomonas with prominent being Lysobacter. Further order level deep phylo-taxonogenomics revealed two major families. One being the original family Xanthomonadaceae and other is proposed as Frateuriaceae fam. nov. as synonym of family Rhodanobacteraceae with novel genus Frateuria gen. nov.

microbiology↗

bioRxiv2022

UVC-based air disinfection system for rapid inactivation of SARS-CoV-2 present in the air

The novel coronavirus disease 2019 (COVID-19) infections have rapidly spread throughout the world, and the virus has acquired an ability to spread via aerosols even at long distances. Hand washing, face-masking, and social distancing are the primary preventive measures against infections. With mounting scientific evidence, World Health Organisation (WHO) declared COVID-19 an air-borne disease. This ensued the need to disinfect air to reduce the transmission. Ultraviolet C (UVC) comprising the light radiation of 200-280 nm range is a commonly used method for inactivation of pathogens. The heating, ventilation, and air conditioning (HVAC) systems are not beneficial in closed spaces due to poor or no ability to damage circulating viruses. Therefore, standard infection-prevention practices coupled with a strategy to reduce infectious viral load in air substantially might be helpful in reducing virus transmissibility. In this study, we implemented UV light-based strategies to combat COVID-19 and future pandemics. We tested various disinfection protocols by using UVC-based air purification systems and currently installed such a system in workspaces, rushed out places, hospitals and healthcare facilities for surface, air, and water disinfection. In this study, we designed a prototype device to test the dose of UVC required to inactivate SARS-CoV-2 in aerosols and demonstrate that the radiation rapidly destroys the virus in aerosols. The UVC treatment renders the virus non-infectious due to chemical modification of nucleic acid. We also demonstrate that UVC treatment alters the Spike protein conformation that may further affect the infectivity of the virus. We show by using a mathematical model based on the experimental data that UVC-based air disinfection strategy can substantially reduce the risk of virus transmission. The systematic treatment by UVC of air in the closed spaces via ventilation systems could be helpful in reducing the active viral load in the air.

microbiology↗

bioRxiv2022

Xanthomonas indica sp. nov., a non-pathogenic bacterium isolated from healthy rice (Oryza sativa) seeds from India

Two yellow pigmented bacterial strains were isolated from healthy rice seeds. The strains designated as PPL560T and PPL568 were identified as members of genus Xanthomonas based on analysis of biochemical and 16S rRNA gene sequence retrieved from whole genome sequence. Isolates formed a distinct monophyletic lineage with X. sontii and X. sacchari as the closest relatives in the phylogenetic tree based on core gene content shared by reported species in genus Xanthomonas. Pairwise ortho Average Nucleotide Identity and digital DNA-DNA hybridisation values calculated against other species of Xanthomonas were below their respective cut-offs. In planta studies revealed that PPL560T and PPL568 are non-pathogenic to rice plants upon leaf clip inoculation. Absence of type III secretion system related genes and effectors further supported their non-pathogenic status. Herein, we propose Xanthomonas indica sp. nov. as novel species of genus Xanthomonas with PPL560T=MTCC13185 as its type strain and PPL568 as another constituent member.

evolutionary biology↗

bioRxiv2022

Systematic hyper-variation and evolution at a lipopolysaccharide locus in the population of Xanthomonas species that infect rice and sugarcane

Advent of high throughput sequencing and population genomics is enabling researchers to investigate selection pressure at hyper-variable genomic loci encoding pathogen-associated molecular patter (PAMP) molecules like lipopolysaccharide (LPS) in an unprecedented manner. Xanthomonas is a model group of phytopathogenic bacteria that infects host in tissue-specific manner. Our in-depth investigation revealed that the successful emergence of lineages infecting major cereals and grasses like rice, sugarcane, and wheat was mediated by acquisition and later replacement of an ancestral type (BXO8) of LPS cassette by distinct one. In the population of the rice xylem pathogen, X. oryzae pv. oryzae (Xoo), the BXO8 is replaced by a distinct BXO1 type of cassette. Alternatively, in diverse Xanthomonas species that infect sugarcane, the BXO8 ancestral cassette has been replaced by yet another kind of Xvv type of LPS cassette, suggesting convergent evolution at an LPS locus mediated by horizontal gene transfer (HGT) events. Aside from xylem, two closely related lineages of X. oryzae that infect parenchyma tissue of rice and Leersia hexandra grass have acquired an LPS cassette from Xanthomonas pathogens that infect citrus, walnut, and strawberry parenchyma, indicating yet another instance of parallel evolution facilitated by HGT. Our targeted and mega-population-based genome dynamic studies revealed potential role of acquisition of specific types of LPS cassettes in the emergence and evolution of tissue specificity in Xanthomonas. Additional cellular, molecular, genetic, and plant studies will help us figure out how a distinct type of LPS help Xanthomonas pathovars and lineages adapt to parenchyma and xylem tissues.

genomics↗

bioRxiv2021

Deep phylo-taxono genomics reveals Xylella as a variant lineage of plant associated Xanthomonas with Stenotrophomonas and Pseudoxanthomonas as misclassified relatives

Genus Xanthomonas is a group of phytopathogens which is phylogenetically related to Xylella, Stenotrophomonas and Pseudoxanthomonas following diverse lifestyles. Xylella is a lethal plant pathogen with highly reduced genome, atypical GC content and is taxonomically related to these three genera. Deep phylo-taxono-genomics reveals that Xylella is a variant Xanthomonas lineage that is sandwiched between Xanthomonas species. Comparative studies suggest the role of unique pigment and exopolysaccharide gene clusters in the emergence of Xanthomonas and Xylella clades. Pan genome analysis identified set of unique genes associated with sub-lineages representing plant associated Xanthomonas clade and nosocomial origin Stenotrophomonas. Overall, our study reveals importance to reconcile classical phenotypic data and genomic findings in reconstituting taxonomic status of these four genera. Significance StatementXylella fastidiosa is a devastating pathogen of perennial dicots such as grapes, citrus, coffee, and olives. The pathogen is transmitted by an insect vector to its specific host wherein the infection leads to complete wilting of the plants. The genome of X. fastidiosa is extremely reduced both in terms of size (2Mb) and GC content (50%) when compared with its relatives such as Xanthomonas, Stenotrophomonas, and Pseudoxanthomonas that have higher GC content (65%) and larger genomes (5Mb). In this study, using systematic and in-depth genome-based taxonomic and phylogenetic criteria along with comparative studies, we assert the need of unification of Xanthomonas with its misclassified relatives (Xylella, Stenotrophomonas and Pseudoxanthomonas). Interestingly, Xylella revealed itself as a minor lineage embedded within two major Xanthomonas lineages comprising member species of different hosts.

genomics↗

bioRxiv2021

Taxonomic repositioning of twelve Xanthomonas campestris, seven Xanthomonas axonopodis and one Pseudomonas cissicola reference pathovars to Xanthomonas citri

Here on the basis of phylo-taxonogenomics criteria we present amended description of 20 pathovars to Xanthomonas citri majority (18/20) of which were first reported from India. 7/20 are currently classified as X. axonopodis, 12/20 as X. campestris and 1/20 as Pseudomonas cissicola. Here, we have generated genome sequence data for 4 pathovars and genomes of remaining 16 were used from the published data. Genome based investigation reveals that all these pathovars belong to X. citri and not to X. axonopodis or X. campestris as previously reported. Present proposal is to aid in resolving the taxonomic confusion of the X. ctiri pathovars and prevent future usage of invalid names.

genomics↗

bioRxiv2021

A bacterial derived plant- mimicking cytokinin hormone regulates social behaviour in a rice pathogen

Many plant-associated bacteria produce plant- mimicking hormones which are involved in modulating host physiology. However, their function in modulating bacterial physiology has not been reported. Here we show that the XopQ protein, a type-III effector of the rice pathogen, Xanthomonas oryzae pv. oryzae (Xoo), is involved in cytokinin biosynthesis. Xoo produces and secretes an active form of cytokinin which enables the bacterium to maintain a planktonic lifestyle and promotes virulence. RNA-seq analysis indicates that the cytokinin produced by Xoo is required for the regulation of several genes which are involved in biofilm formation. We have also identified the Xoo isopentenyl transferase gene, which is involved in the cytokinin biosynthesis pathway and is required for maintaining planktonic behaviour and virulence. Furthermore, mutations in the predicted cytokinin receptor kinase (PcrK) and the downstream response regulator (PcrR) of Xoo phenocopy the cytokinin biosynthetic mutants, but are not complemented by supplementation with exogenous cytokinin. Cytokinin biosynthetic functions are encoded in a number of diverse bacterial genomes suggesting that cytokinin may be a widespread signalling molecule in the bacterial kingdom.

microbiology↗

bioRxiv2021

Global transcriptome analysis of Stenotrophomonas maltophilia in response to growth at human body temperature

Stenotrophomonas maltophilia (Smal) is a typical example of an environmental originated opportunistic human pathogen, which can thrive at different habitats including the human body and can cause a wide range of infections. It must cope with heat stress during transition from the environment to the human body as the physiological temperature of the human body (37 {square}) is higher than environmental niches (22-30 {square}). Interestingly, S. rhizophila a phylogenetic neighbour of Smal within genus Stenotrophomonas is unable to grow at 37 {square}. Thus, it is crucial to understand how Smal is adapted to human body temperature, which could suggest its evolution as an opportunistic human pathogen. In this study, we have performed comparative transcriptome analysis of S. maltophilia grown at 28 {square} and 37 {square} as temperature representative for environmental niches and human body respectively. RNA-Seq analysis revealed several interesting findings showing alterations in gene expression levels at 28 {square} and 37 {square}, which can play an important role during infection. We have observed downregulation of genes involved in cellular motility, energy production and metabolism, replication and repair whereas upregulation of VirB/D4 Type IV secretion system, aerotaxis, cation diffusion facilitator family transporter and LacI family transcriptional regulators at 37 {square}. Microscopy and plate assays corroborated altered expression of genes involved in motility. The results obtained enhance our understanding of the strategies employed by S. maltophilia during adaptation towards the human body. Impact statementStenotrophomonas maltophilia (Smal) is a WHO listed multidrug resistant nosocomial pathogen. Interestingly, S. maltophilia species can grow both at 28 {square} and 37 {square} unlike its closest taxonomic relative, i.e., S. rhizophila and also majority species belonging this genus. Hence this ability to grow at 37 {square}, i.e., human body temperature might have played key role in the unique success and emergence of this species as opportunistic human pathogen. Using transcriptome sequencing, we have identified set of genes which are differentially regulated at 37 {square} and investigated their evolutionary history. This study has revealed regulation of genes involved in motility, metabolism, energy, replication, transcription, aerotaxis and a type IV secretion system might have a role in successful adaption to a distinct lifestyle. The findings will be helpful in further systematic studies on understanding and management of an emerging human pathogen such as Smal.

microbiology↗

bioRxiv2020

Discerning role of a functional arsenic resistance cassette in evolution and adaptation of a rice pathogen

Arsenic (As) is highly toxic element to all forms of life and is a major environmental contaminant. Understanding acquisition, detoxification, and adaptation mechanisms in bacteria that are associated with host in arsenic-rich conditions can provide novel insights into dynamics of host-microbe-microenvironment interactions. In the present study, we have investigated an arsenic resistance mechanism acquired during the evolution of a particular lineage in the population of Xanthomonas oryzae pv. oryzae (Xoo), which is a serious plant pathogen infecting rice. Our study revealed the horizontal acquisition of a novel chromosomal 12kb ars cassette in Xoo IXO1088 that confers high resistance to arsenate/arsenite. The ars cassette comprises several genes that constitute an operon induced in the presence of arsenate/arsenite. Transfer of cloned ars cassette to Xoo BXO512 lacking it confers arsenic resistance phenotype. Further, the transcriptional response of Xoo IXO1088 under arsenate/arsenite exposure was analyzed using RNA sequencing. Arsenic detoxification and efflux, oxidative stress, iron acquisition/storage, and damage repair are the main cellular responses to arsenic exposure. Our investigation has provided novel insights in to how a pathogenic bacterium is coping with arsenic-rich unique micro-environments like seen in rice growing in submerged water conditions. Impact statementArsenic accumulation in rice is a serious and unique agronomic issue. Arsenic contaminated groundwater used for irrigation purposes is adding to the accumulation of arsenic in rice. Submerged conditions in the paddy fields further induce the prevalence of toxic inorganic arsenic species in the environment. Our genomics and transcriptomics-based study reveals how a rice pathogen is coping with the lethal concentrations of arsenic by acquiring a novel resistance cassette during diversification into lineages. Acquisition of such detoxification mechanisms can provide a selective advantage to the bacterial population in avoiding toxicity or enhancing virulence and to their on-going evolutionary events. While there are numerous studies on plant-pathogen-environment interactions, our study highlights the importance of systematic studies on the role of unique micro-environmental conditions on the evolution of host-adapted pathogens/microbes.

microbiology↗