Biology subjects

Kearns, D. B.

Publications and source records attributed to Kearns, D. B..

3 recordsLinked to original sources

bioRxiv2019

Bacterial Hyperswarming as a Protective Response to Intestinal Stress

Bacterial swarming, a collective movement on a surface, has rarely been associated with human pathophysiology. Here, we report for the first time that bacterial swarmers are associated with protection against intestinal inflammation. We show that bacterial swarmers are highly predictive of intestinal stress in mice and humans. We isolated a novel Enterobacter swarming strain, SM3, from mouse feces. SM3 and other known commensal swarmers contrast to their respective swarming-deficient, but swimming-competent isogenic strains abrogated intestinal inflammation in mice. Treatment of colitic mice with SM3, but not its mutants, enriched beneficial fecal anaerobes belonging to the family, Bacteroidales S24-7. We observed SM3 swarming associated pathways in the in vivo fecal metatranscriptomes. In vitro growth of S24-7 was enriched in presence of SM3 or its mutants conjecturing that bacterial swarming in vivo might influence SM3s access to S24-7 in the intestines. Overall, our work identifies a new paradigm in which intestinal stress allows for the emergence of swarming bacteria, which can counterintuitively heal intestinal inflammation.

microbiology↗

bioRxiv2019

Biosurfactant production maintains viability in anoxic conditions by depolarizing the membrane in Bacillus subtilis

The presence or absence of oxygen in the environment is a strong effector of cellular metabolism and physiology. Like many eukaryotes and some bacteria, Bacillus subtilis is an obligate aerobe that primarily utilizes oxygen during respiration to generate ATP. Despite the importance of oxygen for B. subtilis survival, we know little about how oxygen is consumed during growth and how populations respond to shifts in oxygen availability. Here, we find that when oxygen was depleted from stationary phase cultures [~]90% of B. subtilis 3610 cells died and lysed due to autolysin activity; the remaining cells maintained colony-forming ability. Interestingly, the domesticated 168 strain maintained a higher optical density than 3610 during oxygen depletion due to the formation of cell-wall-less protoplasts, but the remaining, rod-shaped cells were >100-fold less viable than 3610. We discovered that the higher viability in 3610 was due to its ability to produce the antibacterial compound surfactin, as surfactin addition rescued 168 viability and also increased yield in aerobic growth. We further demonstrate that surfactin strongly depolarizes the B. subtilis membrane, and that other known membrane-potential disruptors restore viability to 168. These findings highlight the importance of surfactin for survival during oxygen-depleted conditions and demonstrate that antimicrobials normally considered harmful can instead benefit cells in stressful conditions when the terminal electron acceptor in respiration is limiting.

microbiology↗

bioRxiv2019

Transcriptional Regulation and Mechanism of SigN (ZpdN), a pBS32 encoded Sigma Factor

Laboratory strains of Bacillus subtilis encodes as many as 16 alternative sigma factors, each dedicated to expressing a unique regulon such as those involved in stress resistance, sporulation, and motility. The ancestral strain of B. subtilis also encodes an additional sigma factor homolog, ZpdN, not found in lab strains due to it being encoded on the large, low copy number plasmid pBS32 that was lost during domestication. DNA damage triggers pBS32 hyper-replication and cell death in a manner that depends on ZpdN but how ZpdN mediates these effects was unknown. Here we show that ZpdN is a bona fide sigma factor that can direct RNA polymerase to transcribe ZpdN-dependent genes and we rename ZpdN to SigN accordingly. Rend-seq analysis was used to determine the SigN regulon on pBS32, and the 5 ends of transcripts were used to predict the SigN consensus sequence. Finally, we characterize the regulation of SigN itself, and show that it is transcribed by at least three promoters: PsigN1, a strong SigA-dependent LexA-repressed promoter, PsigN2, a weak SigA-dependent constitutive promoter, and PsigN3, a SigN-dependent promoter. Thus, in response to DNA damage LexA is derepressed, SigN is expressed and then experiences positive feedback. How cells die in a pBS32-dependent manner remains unknown, but we predict that death is the product of expressing one or more genes in the SigN regulon.\n\nIMPORTANCESigma factors are utilized by bacteria to control and regulate gene expression. Extra cytoplasmic function sigma factors are activated during times of stress to ensure the survival of the bacterium. Here, we report the presence of a sigma factor that is encoded on a plasmid that leads to cellular death after DNA damage.

microbiology↗