Biology subjects

Gibbs, K. A.

Publications and source records attributed to Gibbs, K. A..

3 recordsLinked to original sources

bioRxiv2018

Swarming bacteria respond to increasing barriers to motility by increasing cell length and modifying colony structure

Organisms can alter morphology and behaviors in response to environmental stimuli such as mechanical forces exerted by surface conditions. The bacterium Proteus mirabilis responds to surface-based growth by enhancing cell length and degree of cell-cell interactions. Cells grow as approximately 2-micrometer rigid rods and independently swim in liquid. By contrast on hard agar surfaces, cells elongate up to 40-fold into snake-like cells that move as a collective group across the surface. Here we have elucidated that individual cell size and degree of cell-cell interactions increased across a continuous gradient that correlates with increasing agar density. We further demonstrate that interactions between the lipopolysaccharide (LPS) component of the outer membrane and the immediate local environment modified these responses by reducing agar-associated barriers to motility. Loss of LPS structures corresponded with increased cell elongation on any given surface. These micrometer-scale changes to cell shape and collective interactions corresponded with centimeter-scale changes in the overall visible structure of the swarm colony. It is well-appreciated in eukaryotes that mechanical forces impact cell shape and migration. Here we propose that bacteria can also dynamically respond to the mechanical forces of surface conditions by altering cell shape, individual motility, and collective migration.

microbiology↗

bioRxiv2017

A proposed chaperone of the bacterial type VI secretion system functions to constrain a self-identity protein

The opportunistic bacterial uropathogen Proteus mirabilis can communicate identity through the export of the self-identity protein, IdsD, via the type VI secretion (T6S) system. Expression of the ids genes provides a fitness advantage during polymicrobial infections in a mouse infection model. Here we provide an answer to the unresolved question of how the activity of a T6S substrate, such as IdsD, is regulated before export. We demonstrate that IdsD is found in clusters that form independently of the T6S machinery and activity. We show that the protein IdsC, which is a member of the proposed DUF4123 chaperone family, is essential for the stability of these clusters as well as the IdsD protein itself. And we provide evidence that amino acid disruptions in IdsC are sufficient to disrupt IdsD export but not IdsD localization into stable subcellular clusters, strongly supporting that IdsC functions in at least two different ways: IdsD stabilization and IdsD export. We propose that IdsC, and likely other DUF4123-containing proteins, function to regulate T6S substrates before export by both stabilizing the protein and mediating export at the T6S machinery.

microbiology↗

bioRxiv2017

A single point mutation in a TssB/VipA homolog disrupts sheath formation in the type VI secretion system of Proteus mirabilis

The type VI secretion (T6S) system is a molecular device for the delivery of proteins from one cell into another. T6S function depends on the contractile sheath comprised of TssB/VipA and TssC/VipB proteins. We previously reported on a mutant variant of TssB that disrupts T6S-dependent export of the self-identity protein, IdsD, in the bacterium Proteus mirabilis. Here we determined the mechanism underlying that initial observation. We show that T6S-dependent export of multiple self-recognition proteins is abrogated in this mutant strain. We have mapped the mutation, which is a single amino acid change, to a region predicted to be involved in the formation of the TssB-TssC sheath. We have demonstrated that this mutation does indeed inhibit sheath formation, thereby explaining the global disruption of T6S activity. We propose that this mutation could be utilized as an important tool for studying functions and behaviors associated with T6S systems.

microbiology↗