Biology subjects

Wiesmann, C. L.

Publications and source records attributed to Wiesmann, C. L..

3 recordsLinked to original sources

bioRxiv2021

The ColR/S two-component system is a conserved determinant of host association across Pseudomonas species

Members of the bacterial genus Pseudomonas form mutualistic, commensal and pathogenic associations with diverse hosts. The prevalence of host association across the genus suggests that symbiosis may be a conserved ancestral trait and that distinct symbiotic lifestyles may be more recently evolved. Here we show that the ColR/S two-component system, part of the Pseudomonas core genome, is functionally conserved between Pseudomonas aeruginosa and Pseudomonas fluorescens. Using plant rhizosphere colonization and virulence in a murine abscess model, we show that colR is required for commensalism with plants and virulence in animals. Comparative transcriptomics revealed that the ColR regulon has diverged between P. aeruginosa and P. fluorescens and deleting components of the ColR regulon revealed strain-specific, but not hostspecific, requirements for ColR-dependent genes. Collectively, our results suggest that ColR/S allows Pseudomonas to sense and respond to a host, but that the ColR-regulon has diverged between Pseudomonas strains with distinct lifestyles.

microbiology↗

bioRxiv2021

Commensal Pseudomonas fluorescens protect Arabidopsis from closely-related Pseudomonas pathogens in a colonization-dependent manner

Plants form commensal associations with soil microorganisms, creating a root microbiome that provides benefits to the host including protection against pathogens. While bacteria can inhibit pathogens through production of antimicrobial compounds in vitro, it is largely unknown how microbiota contribute to pathogen protection in planta. We developed a gnotobiotic model system consisting of Arabidopsis thaliana, and an opportunistic pathogen Pseudomonas sp. N2C3, to identify mechanisms that determine the outcome of plant-pathogen-microbiome interactions in the rhizosphere. We screened 25 phylogenetically diverse Pseudomonas strains for their ability to protect against N2C3 and found that commensal strains closely related to N2C3 were more likely to protect against pathogenesis. We used a comparative genomics approach to identify unique genes in the protective strains that revealed no genes that correlate with protection, suggesting that variable regulation of components of the core Pseudomonas genome may contribute to pathogen protection. We found that commensal colonization level was highly predictive of protection and so tested deletions in genes previously shown to be required for Arabidopsis rhizosphere colonization. We identified a response regulator colR that is required for Pseudomonas protection from N2C3 and fitness in competition with N2C3 indicating that competitive exclusion may contribute to pathogen protection. We found that Pseudomonas WCS365 also protects against the agricultural pathogen Pseudomonas fuscovaginae SE-1, the causal agent of bacterial sheath brown rot of rice. This work establishes a gnotobiotic model to uncover mechanisms by which members of the microbiome can protect hosts from pathogens and informs our understanding of the use of beneficial strains for microbiome engineering in dysbiotic soil systems.

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↗