Campylobacter jejuni promotes commensalism in the intestinal tracts of avian hosts and diarrheal disease in humans, yet components of intestinal environments recognized as spatial cues specific for different intestinal regions by the bacterium to initiate interactions in either host are mostly unknown. By analyzing a C. jejuni acetogenesis mutant defective in converting acetyl coenzyme A (Ac-CoA) to acetate and commensal colonization of young chicks, we discovered evidence for in vivo microbiota-derived short-chain fatty acids (SCFAs) and organic acids as cues recognized by C. jejuni that modulate expression of determinants required for commensalism. We identified a set of C. jejuni genes encoding catabolic enzymes and transport systems for amino acids required for in vivo growth whose expression was modulated by SCFAs. Transcription of these genes was reduced in the acetogenesis mutant but was restored upon supplementation with physiological concentrations of the SCFAs acetate and butyrate present in the lower intestinal tracts of avian and human hosts. Conversely, the organic acid lactate, which is abundant in the upper intestinal tract where C. jejuni colonizes less efficiently, reduced expression of these genes. We propose that microbiota-generated SCFAs and lactate are cues for C. jejuni to discriminate between different intestinal regions. Spatial gradients of these metabolites likely allow C. jejuni to locate preferred niches in the lower intestinal tract and induce expression of factors required for intestinal growth and commensal colonization. Our findings provide insights into the types of cues C. jejuni monitors in the avian host for commensalism and likely in humans to promote diarrheal disease.

Upon starvation, a dense population of rod-shaped Myxococcus xanthus bacteria coordinate their movements to construct mounds in which some of the cells differentiate to spherical spores. During this process of fruiting body formation, short-range C-signaling between cells regulates their movements and the expression of genes important for sporulation. C-signaling activates FruA, a transcription factor that binds cooperatively with another transcription factor, MrpC2, upstream of the fmgA and fmgBC promoters, activating transcription. We have found that a third C-signal-dependent gene, herein named fmgD, is subject to combinatorial control by FruA and MrpC2. The two proteins appear to bind cooperatively upstream of the fmgD promoter and activate transcription. FruA binds proximal to the fmgD promoter, as in the fmgBC promoter region, whereas MrpC2 binds proximal to the fmgA promoter. A novel feature of the fmgD promoter region is the presence of a second MrpC2 binding site partially overlapping the promoter and therefore likely to mediate repression. The downstream MrpC2 site appears to overlap the FruA site, so the two transcription factors may compete for binding, which in both cases appears to be cooperative with MrpC2 at the upstream site. We propose that binding of MrpC2 to the downstream site represses fmgD transcription until C-signaling causes the concentration of active FruA to increase sufficiently to outcompete the downstream MrpC2 for cooperative binding with the upstream MrpC2. This would explain why fmgD transcription begins later during development and is more dependent on C-signaling than transcription of fmgA and fmgBC.

bIntramembrane metalloproteases (IMMPs) control critical biological processes by cleaving membrane-associated proteins within a transmembrane segment or at a site near the membrane surface. Phylogenetic analysis divides IMMPs into four groups. SpoIVFB is a group III IMMP that regulates Bacillus subtilis endospore formation by cleaving Pro-K and releasing the active sigma factor from a membrane. To elucidate the enzyme-substrate interaction, single-cysteine versions of catalytically inactive SpoIVFB and C-terminally truncated Pro-K (1-126) (which can be cleaved by active SpoIVFB) were coexpressed in Escherichia coli, and proximity was tested by disulfide cross-linking in vivo. As expected, the results provided evidence that catalytic residue Glu-44 of SpoIVFB is near the cleavage site in the substrate. Also near the cleavage site were two residues of SpoIVFB in predicted conserved loops; Pro-135 in a short loop and Val-70 in a longer loop. Pro-135 corresponds to Pro-399 of RseP, a group I IMMP, and Pro-399 was reported previously to interact with substrate near the cleavage site, suggesting a conserved interaction across IMMP subfamilies. Val-70 follows a newly recognized conserved motif, PXGG (X is a large hydrophobic residue), which is in a hydrophobic region predicted to be a membrane reentrant loop. Following the hydrophobic region is a negatively charged region that is conserved in IMMPs of groups I and III. At least two residues with a negatively charged side chain are required in this region for activity of SpoIVFB. The region exhibits other features in IMMPs of groups II and IV. Its possible roles, as well as that of the short loop, are discussed. New insights into IMMP-substrate interaction build toward understanding how IMMPs function and may facilitate manipulation of their activity.

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Background Sepsis is a life-threatening condition with high rates of morbidity and mortality; effective and appropriate antibiotic therapy is essential for ensuring patient improvement. To aid in the diagnosis of sepsis, blood cultures are drawn and sent to the microbiology laboratory for pathogen growth, identification, and susceptibility testing. The clinical microbiology laboratory can assist the medical team by providing timely identification of the pathogen(s) causing the bloodstream infection through the use of rapid diagnostic technology. One of these rapid diagnostic technologies, MALDI-TOF MS, has been proven to reduce the time required for appropriate antibiotic therapy when used to identify pathogens grown in culture. This technology has also been used to identify pathogens directly from the positive blood cultures with great success. Content In this minireview, we summarize the different methods that have been developed to directly identify pathogens from positive blood cultures by use of MALDI-TOF MS and the effect of this technology on patient outcomes. Additionally, we touch on current research in the field, including the identification of antimicrobial resistance directly from positive blood cultures by MALDI-TOF MS. Summary Rapid identification of pathogens is important in the survival of patients undergoing a septic event. MALDI-TOF MS technology has played an important role in rapid identification, which has led to a reduction in the time to appropriate antibiotic therapy and contributed to the improvement of patient outcomes. The high sensitivity and specificity of MALDI-TOF MS identification, in combination with MALDI-TOF's rapid function and reduced labor costs, make this technology an attractive choice for clinical laboratories.