Secondary metabolite production of Bacillus spp
Abstract
Bacteria live around us and can be found everywhere in the environment where they are able to exploit available nutrients. Due to the numbers of organisms in these environments, there is significant competition for the available resources, which has resulted in the evolution of bacterial species with diverse strategies to ensure their survival. We aimed to identify and characterize the biosynthetic genes for “antisocial compounds” (e.g., those that reduce the fitness of neighboring bacteria) present in Bacillus species, and to determine if they can be exploited as selection markers or potentially as novel anti-bacterials.
We analysed a diverse set of Bacillus spp. (74 strains) for a “negative” interaction against Bacillus subtilis 168CA in co-culture. In the primary screening, 10 strains were identified as having a strong inhibitory effect on the growth of Bacillus subtilis 168CA. Of these strains a number of these species were strains of Bacillus thuringiensis. We subsequently focused on Bacillus thuringiensis S461, since it showed the most reliable and significant inhibition of the growth Bacillus subtilis 168CA. Bacillus thuringiensis is a Gram-positive bacterium, commonly found in soil and has been studied extensively because it produces insecticidal proteins. But there has been little investigation of its interaction with other bacterial species. In this thesis, I have analysed the chromosomal DNA of Bacillus thuringiensis S461 by anti-SMASH software, revealing 9 gene clusters that were predicted to be involved in the biosynthesis inhibitory compound(s). One of the nine gene clusters, identified as a siderophore compound, was then studied in more detail. Using a combination of cell biology and genetic screening, we found that the siderophore (sid cluster) was not directly involved in the growth inhibition of 168CA, but rather it was required by the strain to assimilate sufficient iron and it seems that this “extra” iron is necessary for the production of the inhibitory compounds that were produced by Bacillus thuringiensis S461.