Research Publications (Food Safety)

Teichoic acids are a diverse class of molecules on the surface of Gram‐positive bacteria known to play important roles in fitness, virulence and bacteriophage susceptibility. A significant level of structural and constitutional heterogeneity exists within the Listeria genus, and it is this variation which serves as a basis for serotyping. Here, we elaborate on recent findings in the Listeria teichoic acid field, and discuss potential diagnostic and therapeutic strategies.

The CodY protein is a global transcriptional regulator of metabolic and virulence genes in low G + C Gram‐positive bacteria, including pathogenic Listeria monocytogenes. Hundreds of CodY‐binding sites were found in the L. monocytogenes genome at near single‐nucleotide resolution, most of them within genes’ coding sequences. In many cases, CodY appears to bind to two overlapping 15‐nt motifs.

Staphylococcus aureus is able to grow in the presence of high concentrations of NaCl but the exact genetic factors contributing to this are unknown. Using a high‐throughput TN‐seq approach, we identified gene 957 as an important factor for the salt stress resistance in S. aureus. A 957‐mutant was not only salt sensitive but also showed increased peptidoglycan crosslinking, altogether highlighting the cell wall as an important barrier against osmotic stress.

DNA phosphorothioation is widely used in antisense drugs. DNA PT modification also exists in bacteria. Using a purified enzyme complex, we show here for the first time how the inert DNA backbone is activated for the exchanging of oxygen with sulfur. Abstract Phosphorothioation (PT) involves the replacement of a nonbridging phosphate oxygen on the DNA backbone with sulfur. In bacteria, the procedure is both sequence‐ and stereo‐specific.

Cobamides are a family of cofactors that are widely‐utilized by diverse organisms, and there are over a dozen variants, including vitamin B12. V. cholerae imports a range of cobamides, but it cannot utilize a variant called pseudocobalamin and instead remodels it through a distinct pathway. Abstract Cobamides are a group of compounds including vitamin B12 that can vary at the lower base position of the nucleotide loop.

Myxococcus xanthus displays several social behaviors involving cell–cell contacts. To understand the role of the lipopolysaccharide (LPS) in these behaviors, we identified key enzymes involved in O‐antigen and LPS biosynthesis: the polyisoprenyl‐phosphate hexose‐1‐phosphate transferase, responsible for priming O‐antigen synthesis and the O‐antigen ligase.

Vibrio cholerae mutants lacking lytic transglycosylases MltC and RlpA are defective for daughter cell separation. Our results suggest that lytic transglycosylases at the division septum serve as a back‐up mechanism to cleave peptidoglycan strands that cannot be cleared by highly‐regulated amidase activity, and to clear peptidoglycan debris that may block the completion of outer‐membrane invagination.

The bacterial pathogen Salmonella Typhimurium invades intestinal epithelial cells. Following invasion, the bacteria can either replicate within a membrane bound vacuole or escape into the cytosol. We show here that SipA, a secreted bacterial protein, facilitates the early survival and/or initiation of replication of cytosolic Salmonella. Summary Salmonella enterica serovar Typhimurium is a facultative intracellular pathogen that invades the intestinal epithelium.

SiiA is required for the function of the Salmonella SPI4‐encoded T1SS. Using structural and functional studies, we show that the periplasmic domain of SiiA displays a peptidoglycan (PG)‐binding OmpA‐like fold and that SiiA binds PG in vitro and in vivo, albeit at an acidic pH, only. SiiA in complex with SiiB translocates protons across the inner membrane; however, further studies are needed to understand how SiiA uses the proton motif force to support the T1SS.

Abstract