The lantibiotic mersacidin is an autoinducing peptide

Dissecting structural and functional diversity of the lantibiotic mersacidin

Mersacidin is a tetracyclic lantibiotic with antibacterial activity against Gram-positive pathogens. To probe the specificity of the biosynthetic pathway of mersacidin and obtain analogs with improved antibacterial activity, an efficient system for generating variants of this lantibiotic was developed. A saturation mutagenesis library of the residues of mersacidin not involved in cycle formation was constructed and used to validate this system. Mersacidin analogs were obtained in good yield in approximately 35% of the cases, producing a collection of 82 new compounds. This system was also used for the production of deletion and insertion mutants of mersacidin. The outcome of these studies suggests that this system can be extended to produce mersacidin variants with multiple changes that will allow a full investigation of the potential use of modified mersacidins as therapeutic agents.

Deciphering the hunting strategy of a bacterial wolfpack

Myxococcus xanthus is a common soil bacterium with an intricate multicellular lifestyle that continues to challenge the way in which we conceptualize the capabilities of prokaryotic organisms. Myxococcus xanthus is the preferred laboratory representative from the Myxobacteria, a family of organisms distinguished by their ability to form highly structured biofilms that include tentacle-like packs of surface-gliding cell groups, synchronized rippling waves of oscillating cells and massive spore-filled aggregates that protrude upwards from the substratum to form fruiting bodies. But most of the Myxobacteria are also predators that thrive on the degradation of macromolecules released through the lysis of other microbial cells. The aim of this review is to examine our understanding of the predatory life cycle of M. xanthus. We will examine the multicellular structures formed during contact with prey, and the molecular mechanisms utilized by M. xanthus to detect and destroy prey cells. We will also examine our understanding of microbial predator-prey relationships and the prospects for how bacterial predation mechanisms can be exploited to generate new antimicrobial technologies.

Lactobacillus acidophilus La-5 increases lactacin B production when it senses live target bacteria

Lactobacillus acidophilus La-5 is a probiotic strain used in dairy products. Production of bacteriocin by L. acidophilus La-5 was achieved when it was grown in co-cultures with the yogurt starter species Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. However, bacteriocin induction was not observed when heat-killed cells were used as inducers. This study demonstrates that L. acidophilus La-5 produces lactacin B and that the bacteriocin expression is controlled by an auto-induction mechanism involving the secreted peptide IP_1800. The transcript level of the lactacin B gene cluster expression was investigated in co-cultures between L. acidophilus La-5 and S. thermophilus STY-31 and a remarkable increase of the bacteriocin structural gene (lbaB) transcription was observed. However, lbaB was transcribed constitutively in uninduced L. acidophilus La-5 cells, but the levels of the secreted bacteriocin were not enough to be detected by the agar diffusion assay. A new method for bacteriocin detection was formulated based on the monitoring on real time of Lactobacillus sakei subsp. sakei growth in presence of the supernatant and the cell wall extracts of pure and induced L. acidophilus La-5. These results showed that part of lactacin B secreted remains adhered to cell envelope.

Development and application of a microtiter plate-based autoinduction bioassay for detection of the lantibiotic subtilin

Production of the lantibiotic subtilin in Bacillus subtilis ATCC 6633 is regulated in a quorum sensing-like mechanism with subtilin acting as autoinducer and signal transduction via the subtilin-specific two-component regulation system SpaRK. Here, we report the construction and application of a subtilin reporter strain in which subtilin induced lacZ gene expression in a B. subtilis ATCC 6633 spaS gene deletion mutant is monitored and visualized by the beta-galactosidase in a chromogenic plate assay. A quantitative microtiter plate subtilin bioassay was developed and optimized. Maximal sensitivity of the system was achieved after 6 h of incubation of the reporter strain together with subtilin in a medium containing 300 mM NaCl. This sensitive and unsusceptible method was applied to identify subtilin producing B. subtilis wild type strains from both, culture collections and soil samples. The B. subtilis lantibiotic ericin S with four amino acid exchanges compared to subtilin induces the subtilin reporter strain, in contrast to the structurally closely related Lactococcus lactis lantibiotic nisin. These observations suggest a certain substrate specificity of the histidine kinase SpaK, which however, also would allow the identification of subtilin-isoform producing microorganisms.