Biology subjects

Geyman, L.

Publications and source records attributed to Geyman, L..

2 recordsLinked to original sources

bioRxiv2024

Quorum sensing employs a dual regulatory mechanism to repress T3SS gene expression

The type III secretion system (T3SS) is a needle-like complex used by numerous bacterial pathogens in host infection by directly injecting exotoxins into the host cell cytoplasm, leading to cell death. The T3SS is a known virulence factor in the shrimp pathogen Vibrio campbellii. The [~]40 genes comprising the V. campbellii T3SS are regulated by a network of transcription factors in response to changes in the cells environment: cell density (quorum sensing; QS), temperature, calcium, and host cell contact. Under positive environmental stimuli, the master T3SS transcription factor ExsA activates expression of the four structural T3SS operons required for needle formation. Previous studies identified a key role of the master QS transcription factor LuxR: repression of exsA transcription via DNA binding at the exsBA promoter. Here we uncovered a new regulatory role of LuxR: indirect post-translational repression of ExsA activity via direct transcriptional repression of the gene encoding the anti-anti-activator ExsC. In V. campbellii, ExsC is a positive regulator of T3SS transcription: high ExsC expression leads to full ExsA transcription activation of the T3SS structural promoters. LuxR binding at the exsC promoter represses transcription of exsC through disruption of ExsA binding. Our findings collectively show that V. campbellii responds to high cell density signals to shut down the expression of the T3SS. We postulate that this dual regulatory mechanism by LuxR enables both the rapid inactivation of existing ExsA protein and blocks its further synthesis, leading to a rapid shutdown of T3SS activity at high cell density. ImportanceVibrio campbellii utilizes the type III secretion system (T3SS) as a mechanism of pathogenesis, which is a highly studied injectisome complex that delivers exotoxins into host cells during infection. The T3SS pathogenicity island in V. campbellii comprises [~]40 genes that are organized into four structural operons. In this study, we determined that quorum sensing - a method of bacterial communication - regulates T3SS genes both at the transcriptional and post-translational levels to shut down T3SS gene expression at high population densities.

microbiology↗

bioRxiv2020

Vibrio campbellii DS40M4 is a tractable model strain that diverges from the canonical quorum-sensing regulatory circuit in vibrios

Vibrio campbellii BB120 (previously classified as Vibrio harveyi) is a fundamental model strain for studying quorum sensing in vibrios. A phylogenetic evaluation of sequenced Vibrio strains in Genbank revealed that BB120 is closely related to the environmental isolate V. campbellii DS40M4. We exploited DS40M4s competence for exogenous DNA uptake to rapidly generate >30 isogenic strains with deletions of genes encoding BB120 quorum-sensing system homologs. Our results show that the quorum-sensing circuit of DS40M4 is distinct from BB120 in three ways: 1) DS40M4 does not produce an acyl homoserine lactone autoinducer but encodes an active orphan LuxN receptor, 2) the quorum regulatory small RNAs (Qrrs) are not solely regulated by autoinducer signaling through the response regulator LuxO, and 3) the DS40M4 quorum-sensing regulon is much smaller than BB120 (~100 genes vs ~400 genes, respectively). Using comparative genomics to expand our understanding of quorum-sensing circuit diversity, we observe that conservation of LuxM/LuxN proteins differs widely both between and within Vibrio species. These strains are also phenotypically distinct: DS40M4 exhibits stronger interbacterial cell killing, whereas BB120 forms more robust biofilms and is bioluminescent. These results underscore the need to examine wild isolates for a broader view of bacterial diversity in the marine ecosystem. Originality-Significance StatementWild bacterial isolates yield important information about traits that vary within species. Here, we compare environmental isolate Vibrio campbellii DS40M4 to its close relative, the model strain BB120 that has been a fundamental strain for studying quorum sensing for >30 years. We examine several phenotypes that define this species, including quorum sensing, bioluminescence, and biofilm formation. Importantly, DS40M4 is naturally transformable with exogenous DNA, which allows for the rapid generation of mutants in a laboratory setting. By exploiting natural transformation, we genetically dissected the functions of BB120 quorum-sensing system homologs in the DS40M4 strain, including two-component signaling systems, transcriptional regulators, and small RNAs.

microbiology↗