Antimicrobials of Bacillus species: mining and engineering

Bacillus sp. have been successfully used to suppress various bacterial and fungal pathogens. Due to the wide availability of whole genome sequence data and the development of genome mining tools, novel antimicrobials are being discovered and updated,;not only bacteriocins, but also NRPs and PKs. A new classification system of known and putative antimicrobial compounds of Bacillus by genome mining is presented in Chapter 2. Importantly, predicting, isolating and screening of Bacillus strains with antimicrobial activity from natural sources keeps showing surprises and underlines the wealth of antimicrobial power these organisms have. Chapter 3 describes the bacterium Bacillus sp. BH072, isolated from a honey sample, with antifungal activities against molds. In order to explain the antifungal activity, the peptides of the fermentation broth were isolated and identified by a combination of several purification methods, and their genes were identified and analyzed. Subsequently in Chapter 4, the genome of Bacillus sp. BH072 was completely sequenced and it was identified to be Bacillus amyloliquefaciens. BAGEL3 mining results showed that the whole mersacidin operon is present in the genome of BH072, while no mersacidin product was obtained by direct production. Considering that the nisin synthetic machinery with additional modification enzymes brings a new opportunity to produce a broader range of lanthipeptides with various modifications, Chapter 5 describes production of class I and II hybrid lantibiotics (nisin and mersacidin) using the nisin leader sequence and NisBC together with GdmD in Lactococcus lactis