Biology subjects

Beskrovnaya, P.

Publications and source records attributed to Beskrovnaya, P..

4 recordsLinked to original sources

bioRxiv2022

The cell envelope of Thermotogae suggests a mechanism for outer membrane biogenesis

The presence of a cell membrane is one of the major structural components defining life. Recent phylogenomic analyses have supported the hypothesis that the last bacterial common ancestor was likely a diderm. Yet, the mechanisms that guided outer membrane (OM) biogenesis remain unknown. Thermotogae is an early-branching phylum with a unique OM, the toga, previously shown to form 2-dimensional arrays of {beta}-barrel trimers. Here we use cryo-electron tomography to characterize the in situ cell envelope architecture of Thermotoga maritima, proteomics and lipidomics to identify the protein and lipid composition of the toga, and bioinformatics to assess the distribution of the major toga components across the phylum. We show that the toga is composed of multiple Omp and {beta}-barrel homologs that represent a highly diverse bipartite OM-tethering system. We further reveal the presence of membrane microdomains ([~]200nm) in the toga that are enriched in phosphatidylethanolamine (PE) lipids required to support the type 4 pilus and the BamA transmembrane complexes. Together, our results highlight a toga-like structure as a possible intermediate between monoderm and diderm cell envelope transitions.

microbiology↗

bioRxiv2020

No endospore formation confirmed in members of the phylum Proteobacteria

Endospore formation is used by members of the phylum Firmicutes to withstand extreme environmental conditions. Several recent studies have documented endospore formation in species outside of Firmicutes, particularly in Rhodobacter johrii and Serratia marcescens, members of the phylum Proteobacteria. Here, we aimed to investigate endospore formation in these two species by using advanced imaging and analytical approaches. Examination of the phase-bright structures observed in R. johrii and S. marcescens using cryo-electron tomography failed to identify endospores or stages of endospore formation. We determined that the phase-bright objects in R. johrii cells were triacylglycerol storage granules and those in S. marcescens were aggregates of cellular debris. In addition, R. johrii and S. marcescens containing phase-bright objects do not possess phenotypic and genetic features of endospores, including enhanced resistance to heat, presence of dipicolinic acid, or the presence of many of the genes associated with endospore formation. Our results support the hypothesis that endospore formation is restricted to the phylum Firmicutes. ImportanceEndospore formation is a mechanism that allows bacteria to generate resilient dormant spores under harsh environmental conditions. Although this process has been traditionally restricted to the largely Gram-positive bacteria of the phylum Firmicutes, recent studies have also described endospores in some Proteobacteria. High complexity of endosporulation, reflected in extensive morphological transformations governed by hundreds of conserved genes, hinders its facile acquisition via horizontal gene transfer. Therefore, ability of distantly related bacteria to produce endospores would imply an ancient nature of this mechanism and potentially a pivotal role in species diversification and outer membrane biogenesis.

microbiology↗

bioRxiv2020

Comparative genomics identified a genetic locus in plant-associated Pseudomonas spp. that is necessary for induced systemic susceptibility

Plant root-associated microbes promote plant growth and induce systemic resistance (ISR) to foliar pathogens. In an attempt to find novel growth-promoting and ISR-inducing strains, we previously identified strains of root-associated Pseudomonas spp. that promote plant growth but unexpectedly induced systemic susceptibility (ISS) rather than ISR to foliar pathogens. Here we demonstrate that the ISS-inducing phenotype is common among root-associated Pseudomonas spp. Using comparative genomics, we identified a single P. fluorescens locus that is unique to ISS strains. We generated a clean deletion of the 11-gene ISS locus and found that it is necessary for the ISS phenotype. Although the functions of the predicted genes in the locus are not apparent based on similarity to genes of known function, the ISS locus is present in diverse bacteria and a subset of the genes have previously been implicated in pathogenesis in animals. Collectively these data show that a single bacterial locus contributes to modulation of systemic plant immunity. ImportanceMicrobiome-associated bacteria can have diverse effects on health of their hosts, yet the genetic and molecular basis of these effects have largely remained elusive. This work demonstrates that a novel bacterial locus can modulate systemic plant immunity. Additionally, this work demonstrates that growth promoting strains may have unanticipated consequences on plant immunity and this is critical to consider when engineering the plant microbiome for agronomic improvement.

microbiology↗

bioRxiv2018

A genome-wide screen identifies genes in rhizosphere-associated Pseudomonas required to evade plant defenses

Pseudomonas fluorescens and related plant root- (\"rhizosphere\") associated species contribute to plant health by modulating defenses and facilitating nutrient uptake. To identify bacterial fitness determinants in the rhizosphere of the model plant Arabidopsis thaliana, we performed a Tn-Seq screen using the biocontrol and growth-promoting strain Pseudomonas sp. WCS365. The screen, which was performed in parallel on wild-type and an immunocompromised Arabidopsis, identified 231 genes that positively affect fitness in the rhizosphere of wild-type plants. A subset of these genes negatively affect fitness in the rhizosphere of immunocompromised plants. We postulated that these genes might be involved in avoiding plant defenses and verified 7 Pseudomonas sp. WCS365 candidate genes by generating clean deletions. We found that two of these deletion strains, {Delta}morA (encodes a putative diguanylate cyclase/phosphodiesterase) and {Delta}spuC (encodes a putrescine aminotransferase) formed enhanced biofilms and inhibited plant growth. Inhibition of plant growth by {Delta}spuC and {Delta}morA was the result of pattern triggered immunity (PTI) as measured by induction of an Arabidopsis PTI reporter and FLS2/BAK1-dependent inhibition of plant growth. We found that MorA acts as a phosphodiesterase to inhibit biofilm formation suggesting a possible role in biofilm dispersal. We found that both putrescine and its precursor arginine promote biofilm formation that is enhanced in the {Delta}spuC mutant, which cannot break down putrescine suggesting that putrescine might serve as a signaling molecule in the rhizosphere. Collectively, this work identified novel bacterial factors required to evade plant defenses in the rhizosphere.\n\nImportanceWhile rhizosphere bacteria hold the potential to improve plant health and fitness, little is known about the bacterial genes required to evade host immunity. Using a model system consisting of Arabidopsis and a beneficial Pseudomonas sp. isolate, we identified bacterial genes required for both rhizosphere fitness and for evading host immune responses. This work advances our understanding of how evasion of host defenses contributes to survival in the rhizosphere.

microbiology↗