Biology subjects

Pavelsky, M.

Publications and source records attributed to Pavelsky, M..

3 recordsLinked to original sources

bioRxiv2025

H-NS is a conserved repressor of the type VI secretion system in Vibrio fischeri

The type VI secretion system (T6SS) is a broadly distributed interbacterial weapon found in both beneficial and pathogenic bacteria and can enhance a microbes ability to colonize a host. Vibrio fischeri is a beneficial symbiont of fish and squid and a model organism for T6SS function, which is activated in high-viscosity conditions. Previously, we isolated an hns mutant in a transposon screen to identify regulators of the T6SS in the fish symbiont V. fischeri MJ11. The hns gene encodes the DNA-binding protein, H-NS, a conserved global regulator of gene expression that aids in adaptation to changing environments. Quantitative transcriptomes of the hns mutant and parent strains grown in liquid or hydrogel media revealed hns is required for the global transcriptional changes that occur during transition from lower to higher viscosity conditions. Furthermore, T6SS gene transcripts are more abundant in the hns mutant in both conditions, suggesting H-NS represses T6SS in the parent. Single-cell fluorescence microscopy confirmed hns mutant cells make more T6SS weapons in both liquid and hydrogel medium, where the hns mutant is more proficient at killing a competitor strain, compared to the wild-type parent. Finally, disrupting the hns gene in additional light organ isolates resulted in a similar derepression of T6SS, indicating H-NS is a conserved repressor of this interbacterial weapon. This work furthers our understanding of the role of H-NS as a global regulator during environmental shifts in a host-associated bacterial symbiont and expands the list of species where H-NS represses T6SS to include V. fischeri.

microbiology↗

bioRxiv2025

Euprymna berryi as a comparative model host for Vibrio fischeri light organ symbiosis

Functional studies of host-microbe interactions benefit from natural model systems that enable exploration of molecular mechanisms at the host-microbe interface. Bioluminescent Vibrio fischeri colonize the light organ of the Hawaiian bobtail squid, Euprymna scolopes, and this binary model has enabled advances in understanding host-microbe communication, colonization specificity, in vivo biofilms, intraspecific competition, and quorum sensing. The hummingbird bobtail squid, Euprymna berryi, can be generationally bred and maintained in lab settings and has had multiple genes deleted by CRISPR approaches. The prospect of expanding the utility of the light organ model system by producing multigenerational host lines led us to determine the extent to which the E. berryi light organ symbiosis parallels known processes in E. scolopes. However, the nature of the E. berryi light organ, including its microbial constituency and specificity for microbial partners, have not been examined. In this report, we isolate bacteria from E. berryi animals and tank water. Assays of bacterial behaviors required in the host, as well as host responses to bacterial colonization, illustrate largely parallel phenotypes in E. berryi and E. scolopes hatchlings. This study reveals E. berryi to be a valuable comparative model to complement studies in E. scolopes. IMPORTANCEMicrobiome studies have been substantially advanced by model systems that enable functional interrogation of the roles of the partners and the molecular communication between those partners. The Euprymna scolopes-Vibrio fischeri system has contributed foundational knowledge, revealing key roles for bacterial quorum sensing broadly and in animal hosts, for bacteria in stimulating animal development, for bacterial motility in accessing host sites, and for in vivo biofilm formation in development and specificity of an animals microbiome. Euprymna berryi is a second bobtail squid host, and one that has recently been shown to be robust to laboratory husbandry and amenable to gene knockout. This study identifies E. berryi as a strong symbiosis model host due to features that are conserved with those of E. scolopes, which will enable extension of functional studies in bobtail squid symbioses.

microbiology↗

bioRxiv2024

The conserved global regulator H-NS has a strain-specific impact on biofilm formation in Vibrio fischeri symbionts

Strain-level variation among host-associated bacteria often determines host range and the extent to which colonization is beneficial, benign, or pathogenic. Vibrio fischeri is a beneficial symbiont of the light organs of fish and squid with known strain-specific differences that impact host specificity, colonization efficiency, and interbacterial competition. Here, we describe how the conserved global regulator, H-NS, has a strain-specific impact on a critical colonization behavior: biofilm formation. We isolated a mutant of the fish symbiont V. fischeri MJ11 with a transposon insertion in the hns gene. This mutant formed sticky, moderately wrinkled colonies on LBS plates, a condition not known to induce biofilm in this species. A reconstructed hns mutant displayed the same wrinkled colony, which became smooth when hns was complemented in trans, indicating the hns disruption is causal for biofilm formation in MJ11. Transcriptomes revealed differential expression for the syp biofilm locus in the hns mutant, relative to the parent, suggesting biofilm may in part involve SYP polysaccharide. However, enhanced biofilm in the MJ11 hns mutant was not sufficient to allow colonization of a non-native squid host. Finally, moving the hns mutation into other V. fischeri strains, including the squid symbionts ES114 and ES401, and seawater isolate PP3, revealed strain-specific biofilm phenotypes: ES114 and ES401 hns mutants displayed minimal biofilm phenotypes while PP3 hns mutant colonies were more wrinkled than the MJ11 hns mutant. These findings together define H-NS as a novel regulator of V. fischeri symbiotic biofilm and demonstrate key strain specificity in that role. ImportanceThis work, which shows how H-NS has strain-specific impacts on biofilm in Vibrio fischeri, underscores the importance of studying multiple strains, even when examining highly conserved genes and functions. Our observation that knocking out a conserved regulator can result in a wide range of biofilm phenotypes, depending on the isolate, serves as a powerful reminder that strain-level variation is common and worthy of exploration. Indeed, uncovering the mechanisms of strain-specific phenotypic differences is essential to understand drivers of niche differentiation and bacterial evolution. Thus, it is important to carefully match the number and type of strains used in a study with the research question to accurately interpret and extrapolate the results beyond a single genotype. The additional work required for multi-strain studies is often worth the investment of time and resources, as it provides a broader view of the complexity of within-species diversity in microbial systems.

microbiology↗