Biology subjects

Benomar, S.

Publications and source records attributed to Benomar, S..

4 recordsLinked to original sources

bioRxiv2022

Cross-species activation of hydrogen cyanide production by a promiscuous quorum-sensing receptor promotes Chromobacterium subtsugae competition in a dual-species model

Many saprophytic bacteria have LuxR-I-type acyl-homoserine lactone (AHL) quorum-sensing systems that may be important for competing with other bacteria in complex soil communities. LuxR AHL receptors specifically interact with cognate AHLs to cause changes in expression of target genes. Some LuxR-type AHL receptors have relaxed specificity and are responsive to non-cognate AHLs. These promiscuous receptors might be used to sense and respond to AHLs produced by other bacteria by eavesdropping. We are interested in understanding the role of eavesdropping during interspecies competition. The soil saprophyte Chromobacterium subtsugae has a single AHL circuit, CviR-I, which produces and responds to N-hexanoyl-HSL (C6-HSL). The AHL receptor CviR can respond to a variety of AHLs in addition to C6-HSL. In prior studies we have utilized a coculture model with C. subtsugae and another soil saprophyte Burkholderia thailandensis. Using this model, we previously showed that promiscuous activation of CviR by B. thailandensis AHLs provides a competitive advantage to C. subtsugae. Here, we show that B. thailandensis AHLs activate transcription of dozens of genes in C. subtsugae, including the hcnABC genes coding for production of hydrogen cyanide. We show that hydrogen cyanide production is population density-dependent and demonstrate that the cross-induction of hydrogen cyanide by B. thailandensis AHLs provides a competitive advantage to C. subtsugae. Our results provide new information on C. subtsugae quorum sensing and are the basis for future studies aimed at understanding the role of eavesdropping in interspecies competition. IMPACT STATEMENTIn quorum sensing, population density-dependent changes in gene regulation are the result of a cytoplasmic transcription regulator binding to a quorum sensing signal. The signal-receptor interaction is considered to be specific to ensure fidelity of the system. However, some quorum-sensing receptor proteins have relaxed specificity and can recognize and respond to a range of signals. These promiscuous receptors might provide some benefit by enabling interspecies activation of quorum sensing by "eavesdropping," although the potential benefits of eavesdropping are not well studied. The current study utilizes a dual-species laboratory competition model, where one species has a promiscuous signal receptor and can respond to signals produced by the other species. In our study, we identify the signals that enable quorum sensing cross talk and show that cross talk promotes competition by inducing hydrogen cyanide production. Our results highlight how quorum sensing-enabled interspecies cross talk might provide an advantage during competition and provide a new basis for understanding how receptor-signal pairs might evolve in natural environments. DATA SUMMARYThe authors confirm all supporting data, code and protocols have been provided within the article or through supplementary data files.

microbiology↗

bioRxiv2021

Plasmid-encoded H-NS controls extracellular matrix composition in a modern Acinetobacter baumannii urinary isolate

Acinetobacter baumannii is emerging as a multidrug-resistant (MDR) nosocomial pathogen of increasing threat to human health worldwide. The recent MDR urinary isolate UPAB1 carries the plasmid pAB5, a member of a family of large conjugative plasmids (LCP). LCP encode several antibiotic resistance genes and repress the type VI secretion system (T6SS) to enable their dissemination, employing two TetR transcriptional regulators. Furthermore, pAB5 controls the expression of additional chromosomally encoded genes, impacting UPAB1 virulence. Here we show that a pAB5-encoded H-NS transcriptional regulator represses the synthesis of the exopolysaccharide PNAG and the expression of a previously uncharacterized three-gene cluster that encodes a protein belonging to the CsgG/HfaB family. Members of this protein family are involved in amyloid or polysaccharide formation in other species. Deletion of the CsgG homolog abrogated PNAG production and Cup pili formation, resulting in a subsequent reduction in biofilm formation. Although this gene cluster is widely distributed in Gram-negative bacteria, it remains largely uninvestigated. Our results illustrate the complex cross-talks that take place between plasmids and the chromosomes of their bacterial host, which in this case can contribute to the pathogenesis of Acinetobacter. IMPORTANCEThe opportunistic human pathogen Acinetobacter baumannii displays the highest reported rates of multidrug resistance among Gram-negative pathogens. Many A. baumannii strains carry large conjugative plasmids like pAB5. In recent years, we have witnessed an increase in knowledge about the regulatory cross-talks between plasmids and bacterial chromosomes. Here we show that pAB5 controls the composition of the bacterial extracellular matrix, resulting in a drastic reduction in biofilm formation. The association between biofilm formation, virulence, and antibiotic resistance is well-documented. Therefore, understanding the factors involved in the regulation of biofilm formation in Acinetobacter has remarkable therapeutic potential.

microbiology↗

bioRxiv2019

Two resistance nodulation division-family efflux pumps in Chromobacterium species and their role in antibiotic resistance and tolerance

Very little is known of the antibiotic resistance mechanisms of members of the Chromobacterium genus. In previous studies of Chromobacterium subtsugae (formerly C. violaceum) strain CV017, we identified a resistance nodulation division (RND)-family efflux pump (CdeAB-OprM). Here, we show the cdeAB-oprM genes are widely distributed in members of the Chromobacterium genus. We use antimicrobial susceptibility testing with a CV017 cdeAB-oprM mutant to show the products of these genes confers resistance to a variety of antibiotics including ciprofloxacin, a clinically important antibiotic. We also identified a related RND-family pump, cseAB-oprN, in the genome of CV017 and other C. subtsugae species, that is not present in other members of the Chromobacterium genus. We demonstrate that CdeAB-OprM and CseAB-OprN are both transcriptionally induced in CV017 cells treated with sub-lethal antibiotic concentrations and they are important for induction of tolerance to different antibiotics. While CdeAB-OprM has a broad antibiotic specificity, the CseAB-OprN system is highly specific for a ribosome-targeting antibiotic produced by the saprophytic bacterium Burkholderia thailandensis, bactobolin. Finally, we use a previously developed B. thailandensis-C. subtsugae CV017 co-culture model to demonstrate that adding sub-lethal bactobolin at the beginning of co-culture growth increases the ability of CV017 to compete with B. thailandensis in a manner that is dependent on the CseAB-OprN system. Our results provide new information on the antibiotic resistance mechanisms of Chromobacterium species and highlight the importance of efflux pumps during competition with other bacterial species. IMPORTANCEThis study describes two closely related efflux pumps in members of the Chromobacterium genus, which includes opportunistic but often-fatal pathogens and species with highly versatile metabolic capabilities. Efflux pumps remove antibiotics from the cell and are important for antibiotic resistance. One of these pumps is broadly distributed in the Chromobacterium genus and increases resistance to clinically relevant antibiotics. The other efflux pump is present only in Chromobacterium subtsugae and is highly specific for bactobolin, an antibiotic produced by the soil saprophyte Burkholderia thailandensis. We demonstrate these pumps can be activated to increase resistance by their antibiotic substrates, and that this activation is important for C. subtsugae to survive in a laboratory competition experiment with B. thailandensis. These results have implications for managing antibiotic-resistant Chromobacterium infections, bioengineering of Chromobacterium species, and for understanding the evolution of efflux pumps.

microbiology↗

bioRxiv2018

The C. elegans CHP1 homolog, pbo-1, functions in innate immunity by regulating the pH of the intestinal lumen

Caenorhabditis elegans are soil-dwelling nematodes and models for understanding innate immunity and infection. Previous work has described a regularly-timed pH change in the intestine of Caenorhabditis elegans called the pH wave. To characterize this wave and its function in the worm, we developed a novel fluorescent dye (KR35) that accumulates in the intestine and sensitively responds to dynamic changes in pH. Here, we use KR35 to show that mutations in the Ca2+-binding protein, PBO-1 abrogate the pH wave, causing the anterior intestine to be constantly acidic. Surprisingly, pbo-1 mutants were also more susceptible to infection by several bacterial pathogens. We could suppress pathogen susceptibility in pbo-1 mutants by treating the animals with pH-buffering bicarbonate, suggesting the pathogen susceptibility is a function of the acidity of the intestinal pH. Furthermore, we use KR35 to show that pathogens completely neutralize the pH in the intestine of wild type, but not pbo-1 mutants. C. elegans is known to increase production of reactive oxygen species (ROS), such as H2O2, in response to pathogens, which is an important component of pathogen defense. We show that pbo-1 mutants exhibited decreased H2O2 in response to pathogens, which could also be partially restored in pbo-1 animals treated with bicarbonate. Ultimately, our results support a model whereby pbo-1 functions during infection to permit pH changes in the intestine that are important for fighting pathogens.\n\nAuthor SummaryInnate immunity is critical for host defense against pathogens. However, questions remain about how the host senses and responds to pathogen invasion. Using a pH-sensitive fluorescent dye and a Caenorhabditis elegans pathogen infection model we show that pathogens induce changes in pH of the worm intestine. We also show that intestinal pH directly affects production of reactive oxygen species (e.g. H2O2) important for pathogen defense. Our results show that pH regulation is an important component of the innate immune response to pathogens.

microbiology↗