Biology subjects

Chepkwony, N. K.

Publications and source records attributed to Chepkwony, N. K..

3 recordsLinked to original sources

bioRxiv2022

HfaE is a component of the holdfast anchor complex that tethers the holdfast adhesin to the cell envelope

Bacteria use adhesins to colonize different surfaces and form biofilms. The species of the Caulobacterales order use a polar adhesin called holdfast, composed of polysaccharides, proteins, and DNA to irreversibly adhere to surfaces. In C. crescentus, a freshwater Caulobacterales, the holdfast is anchored at the cell pole via the holdfast anchor (Hfa) proteins HfaA, HfaB, and HfaD. HfaA and HfaD co-localize with holdfast and are thought to form amyloid-like fibers that anchor holdfast to the cell envelope. HfaB, a lipoprotein, is required for translocation of HfaA and HfaD to the cell surface. Deletion of the anchor proteins leads to a severe defect in adherence resulting from holdfast not properly attached to the cell and shed into the medium. This phenotype is greater in a {Delta}hfaB than a double {Delta}hfaA hfaD mutant, suggesting that HfaB has other functions besides the translocation of HfaA and HfaD. Here, we identify an additional HfaB-dependent holdfast anchoring protein, HfaE, which is predicted to be a secreted protein. HfaE is highly conserved among Caulobacterales species with no predicted function. In planktonic culture, hfaE mutants produce holdfasts and rosettes similar to wild type. However, holdfasts from hfaE mutants bind to the surface but are unable to anchor cells, similar to other anchor mutants. We showed that fluorescently-tagged HfaE co-localizes with holdfast, and HfaE forms an SDS-resistant high molecular weight species consistent with amyloid fiber formation. We propose that HfaE is a novel holdfast anchor protein, and that HfaE functions to link holdfast material to the cell envelope. IMPORTANCEFor surface attachment and biofilm formation, bacteria produce adhesins that are composed of polysaccharides, proteins and DNA. Species in the Caulobacterales produce a specialized polar adhesin, holdfast, which is required for permanent attachment to surfaces. In this study, we evaluate the role of a newly identified holdfast anchor protein HfaE in holdfast anchoring to the cell surface in two different Caulobacterales with drastically different environments. We show that HfaE plays an important role in adhesion and biofilm formation in Caulobacterales. Our results provide insights into bacterial adhesins and how they interact with the cell envelope and surfaces.

microbiology↗

bioRxiv2021

A polysaccharide deacetylase enhances bacterial adhesion in high ionic strength environments

The adhesion of organisms to surfaces in aquatic environments provides a diversity of benefits such as better access to nutrients or protection from the elements or from predation. Differences in ionic strength, pH, temperature, shear forces, and other environmental factors impact adhesion and organisms have evolved various strategies to optimize their adhesins for their specific environmental conditions. We know essentially nothing about how bacteria evolved their adhesive mechanisms to attach efficiently in environments with different physico-chemical conditions. Many species of Alphaproteobacteria, including members of the order Caulobacterales, use a polar adhesin, called holdfast, for surface attachment and subsequent biofilm formation in both freshwater and marine environments. Hirschia baltica, a marine member of Caulobacterales, produces a holdfast adhesin that tolerates a drastically higher ionic strength than the holdfast produced by its freshwater relative, Caulobacter crescentus. In this work, we show that the holdfast polysaccharide deacetylase HfsH plays an important role in adherence in high ionic strength environments. We show that deletion of hfsH in H. baltica disrupts holdfast binding properties and structure. Increasing expression of HfsH in C. crescentus improved holdfast binding in high salinity, whereas lowering HfsH expression in H. baltica reduced holdfast binding at high ionic strength. We conclude that HfsH plays a role in modulating holdfast binding at high ionic strength and hypothesize that this modulation occurs through varied deacetylation of holdfast polysaccharides.

microbiology↗

bioRxiv2019

Comparative analysis of ionic strength tolerance between freshwater and marine Caulobacterales adhesins

Bacterial adhesion is affected by environmental factors, such as ionic strength, pH, temperature, and shear forces, and therefore marine bacteria must have developed holdfasts with different composition and structures than their freshwater counterparts to adapt to their natural environment. The dimorphic -proteobacterium Hirschia baltica is a marine budding bacterium in the Caulobacterales clade. H. baltica uses a polar adhesin, the holdfast, located at the cell pole opposite the reproductive stalk for surface attachment and cell-cell adhesion. The holdfast adhesin has been best characterized in Caulobacter crescentus, a freshwater member of the Caulobacterales, and little is known about holdfast composition and properties in marine Caulobacterales. Here we use H. baltica as a model to characterize holdfast properties in marine Caulobacterales. We show that freshwater and marine Caulobacterales use similar genes in holdfast biogenesis and that these genes are highly conserved among the two genera. We also determine that H. baltica produces larger holdfast than C. crescentus and that those holdfasts have a different chemical composition, as they contain N-acetylglucosamine and galactose monosaccharide residues and proteins, but lack DNA. Finally, we show that H. baltica holdfasts tolerate higher ionic strength than those of C. crescentus. We conclude that marine Caulobacterales holdfasts have physicochemical properties that maximize binding in high ionic strength environments.\n\nIMPORTANCEMost bacteria spend a large amount of their lifespan attached to surfaces, forming complex multicellular communities called biofilms. Bacteria can colonize virtually any surface, therefore they have adapted to bind efficiently in very different environments. In this study, we compare the adhesive holdfasts produced by the freshwater bacterium C. crescentus and a relative, the marine bacterium H. baltica. We show that H. baltica holdfasts have a different morphology and chemical composition, and tolerate high ionic strength. Our results show that H. baltica holdfast is an excellent model to study the effect of ionic strength on adhesion and providing insights on the physicochemical properties required for adhesion in the marine environment.

microbiology↗