Bacillus subtilis enhances production of Paracin1.7, a bacteriocin produced by Lactobacillus paracasei HD1-7, isolated from Chinese fermented cabbage

Enhancing chemical and biological diversity by co-cultivation

In natural product research, microbial metabolites have tremendous potential to provide new therapeutic agents since extremely diverse chemical structures can be found in the nearly infinite microbial population. Conventionally, these specialized metabolites are screened by single-strain cultures. However, owing to the lack of biotic and abiotic interactions in monocultures, the growth conditions are significantly different from those encountered in a natural environment and result in less diversity and the frequent re-isolation of known compounds. In the last decade, several methods have been developed to eventually understand the physiological conditions under which cryptic microbial genes are activated in an attempt to stimulate their biosynthesis and elicit the production of hitherto unexpressed chemical diversity. Among those, co-cultivation is one of the most efficient ways to induce silenced pathways, mimicking the competitive microbial environment for the production and holistic regulation of metabolites, and has become a golden methodology for metabolome expansion. It does not require previous knowledge of the signaling mechanism and genome nor any special equipment for cultivation and data interpretation. Several reviews have shown the potential of co-cultivation to produce new biologically active leads. However, only a few studies have detailed experimental, analytical, and microbiological strategies for efficiently inducing bioactive molecules by co-culture. Therefore, we reviewed studies applying co-culture to induce secondary metabolite pathways to provide insights into experimental variables compatible with high-throughput analytical procedures. Mixed-fermentation publications from 1978 to 2022 were assessed regarding types of co-culture set-ups, metabolic induction, and interaction effects.

Bacillus subtilis BS-15 Effectively Improves Plantaricin Production and the Regulatory Biosynthesis in Lactiplantibacillus plantarum RX-8

Plantaricin is a broad-spectrum bacteriocin produced by Lactiplantibacillus plantarum with significant food industry application potential. It was found that the plantaricin production of L. plantarum RX-8 was enhanced when co-culturing with Bacillus subtilis BS-15. This study, therefore, set out to explore how B. subtilis BS-15 induces biosynthesis of plantaricin. The effect of co-culturing with B. subtilis BS-15 on cell growth, plantaricin production, quorum-sensing (QS) signal molecule PlnA/autoinducer-2 (AI-2) secretion, as well as plantaricin biosynthesis gene cluster and AI-2 synthesis-associated gene expression, was investigated in bacteriocin-producer L. plantarum RX-8. When L. plantarum RX-8 and B. subtilis BS-15 were co-inoculated in Man–Rogosa–Sharp (MRS) for 20 h at an inoculum ratio of 1:1 (10⁶:10⁶ CFU/ml), the greatest plantaricin output (2,048 AU/ml) was obtained, rising by 32-fold compared with the monoculture of L. plantarum RX-8. Additionally, co-culture increased PlnA-inducing activity and AI-2 activity by 8- and 1.14-fold, respectively, over monoculture. RT-qPCR findings generated every 4 h (4–32 h) demonstrated that B. subtilis BS-15 remarkably improved the transcription of plnABCD and plnEF, and increased pfs and luxS transcription, even when using 200 mM D-ribose, a kind of AI-2 inhibitor. Based on the above findings, co-culturing with B. subtilis BS-15 as an environmental stimulus could activate the plantaricin induction via the PlnA-mediated intraspecies QS system and the AI-2-mediated interspecies QS system. Moreover, the inducing effect of PlnA and AI-2 in co-culture was independent. Differential proteomics analysis of B. subtilis BS-15 in co-culture indicated that bacteriocin-inducing regulatory mechanism may be related to flagellar assembly, peptidoglycan biosynthesis, anaerobic respiration, glycine cleavage system, or thiamin pyrophosphate biosynthesis.

Bacteriocin production and inhibition of Bacillus subtilis by Lactobacillus paracasei HD1.7 in an indirect coculture system

A broad-spectrum antimicrobial peptide named Paracin 1.7 was produced by Lactobacillus paracasei HD1.7, which was isolated from Chinese sauerkraut juice. In this study, the influence of cocultivation on the communication mechanism of L. paracasei HD1.7 and Bacillus subtilis was investigated. The two bacterial strains were grown in monoculture and indirect coculture, and the growth of both bacteria and bacteriocin production as well as the transcriptional level of luxS in L. paracasei HD1.7 and spo0A in B. subtilis were monitored. Bacteriocin production and cell numbers were increased significantly when L. paracasei HD1.7 cells were indirectly cocultured with B. subtilis, and bacteriocin-producing L. paracasei HD1.7 can prevent the growth and sporulation of B. subtilis. After indirect coculture with B. subtilis, the expression of luxS in L. paracasei HD1.7 increased in the exponential growth phase and decreased in the stationary phase compared to monoculture. The expression of spo0A in B. subtilis dropped in the indirect coculture compared to the monoculture. It indicate that the upregulation of luxS is due to a response to a secreted compound produced by B. subtilis. The results show L. paracasei HD1.7 has an amensalism on B. subtilis, while B. subtilis has a commensalism on L. paracasei HD1.7.