Biology subjects

Brun, Y. V.

Publications and source records attributed to Brun, Y. V..

4 recordsLinked to original sources

bioRxiv2018

Beating Swords into Ploughshares: Domestication of a Phage Lysin for Housekeeping Function

Temperate phages constitute a potentially beneficial genetic reservoir for bacterial innovation despite being selfish entities encoding an infection cycle inherently at odds with bacterial fitness. These phages integrate their genomes into the bacterial host during infection, donating new, but deleterious, genetic material: the phage genome encodes toxic genes, such as lysins, that kill the bacterium during the phage infection cycle. Remarkably, some bacteria have exploited the destructive properties of phage genes for their own benefit by co-opting them as toxins for functions related to bacterial warfare, virulence, and secretion. However, do toxic phage genes ever become raw material for functional innovation? Here we report on a toxic phage gene whose product has lost its toxicity and has become a domain of a core cellular factor, SpmX, throughout the bacterial order Caulobacterales. Using a combination of phylogenetics, bioinformatics, structural biology, cell biology, and biochemistry, we have investigated the origin and function of SpmX and determined that its occurrence is the result of the detoxification of a phage peptidoglycan hydrolase gene. We show that the retained, attenuated activity of the phage-derived domain plays an important role in proper cell morphology and developmental regulation in representatives of this large bacterial clade. To our knowledge, this is the first observation of phage gene domestication in which a toxic phage gene has been co-opted for a housekeeping function.

microbiology↗

bioRxiv2018

Diverse spatial organization of photosynthetic membranes among purple nonsulfur bacteria

In diverse bacteria, proper cellular physiology requires the utilization of protein- or membrane-bound compartments that afford specific metabolic capabilities. One such compartment is the light-harvesting intracytoplasmic membrane (ICM) of purple nonsulfur bacteria (PNSB). Here we reveal that ICMs are subject to differential spatial organization among PNSB. We visualized ICMs in live cells of fourteen PNSB species by exploiting the natural autofluorescence of the photosynthetic machinery. We then quantitatively characterized ICM localization using automated computational analysis of autofluorescence patterns within single cells across the population. Our studies revealed that ICMs are localized in distinct subcellular patterns that differ between species; some PNSB elaborate ICMs throughout the cell, while others spatially restrict ICM to varying degrees. The most highly-restricted ICMs were localized in a specific pattern corresponding to progression of cell growth and division. An identical pattern of ICM restriction was conserved across at least two genera. Phylogenetic and phenotypic comparisons established that ICM localization and ICM architecture are not strictly interdependent and that neither trait fully correlates with the evolutionary relatedness of the species. This discovery of new diversity in bacterial cell organization has implications for understanding both the mechanisms underpinning spatial arrangement of bacterial compartments and the potential benefits of adopting different spatiotemporal patterns.

microbiology↗

bioRxiv2017

Layered structure and complex mechanochemistry of a strong bacterial adhesive

While designing adhesives that perform in aqueous environments has proven challenging for synthetic adhesives, microorganisms commonly produce bioadhesives that efficiently attach to a variety of substrates, including wet surfaces that remain a challenge for industrial adhesives. The aquatic bacterium Caulobacter crescentus uses a discrete polar polysaccharide complex, the holdfast, to strongly attach to surfaces and resist flow. The holdfast is extremely versatile and has an impressive adhesive strength. Here, we use atomic force microscopy (AFM) to unravel the complex structure of the holdfast and characterize its chemical constituents and their role in adhesion. We used purified holdfasts to dissect the intrinsic properties of this component as a biomaterial, without the effect of the bacterial cell body. Our data support a model where the holdfast is a heterogeneous material composed of two layers: a stiff nanoscopic core, covered by a sparse, flexible brush layer. These two layers contain not only N-acetyl-D-glucosamine (NAG), the only yet identified component present in the holdfast, but also peptides and DNA, which provide structure and adhesive character. Biochemical experiments suggest that, while polypeptides are the most important components for adhesive force, the presence of DNA mainly impacts the brush layer and initial adhesion, and NAG plays a primarily structural role within the core. Moreover, our results suggest that holdfast matures structurally, becoming more homogeneous over time. The unanticipated complexity of both the structure and composition of the holdfast likely underlies its distinctive strength as a wet adhesive and could inform the development of a versatile new family of adhesives.

biophysics↗

bioRxiv2017

Obstruction of pilus retraction stimulates bacterial surface sensing

Surface association provides numerous fitness advantages to bacteria. Thus, it is critical for bacteria to recognize surface contact and to consequently initiate physiological changes required for a surface-associated lifestyle (1). Ubiquitous microbial appendages called pili are involved in sensing surfaces and mediating downstream surface-associated behaviors (2-6). The mechanism by which pili mediate surface sensing remains unknown, largely due to the difficulty to visualize their dynamic nature and to directly modulate their activity without genetic modification. Here, we show that Caulobacter crescentus pili undergo dynamic cycles of extension and retraction that cease within seconds of surface contact, and this arrest of pilus activity coincides with surface-stimulated holdfast synthesis. By physically blocking pili, we show that imposing resistance to pilus retraction is sufficient to stimulate holdfast synthesis in the absence of surface contact. Thus, resistance to type IV pilus retraction upon surface attachment is used for surface sensing.\n\nOne Sentence SummaryBacteria use the tension imparted on retracting pilus fibers upon their binding to a surface for surface sensing.

microbiology↗