Influence of B. subtilis 3NA mutations in spo0A and abrB on surfactin production in B. subtilis 168

Background Bacillus subtilis is a well-established host for a variety of bioproduction processes, with much interest focused on the production of biosurfactants such as the cyclic lipopeptide surfactin. Surfactin production is tightly intertwined with quorum sensing and regulatory cell differentiation processes. As previous studies have shown, a non-sporulating B. subtilis strain 3NA encoding a functional sfp locus but mutations in the spo0A and abrB loci, called JABs32, exhibits noticeably increased surfactin production capabilities. In this work, the impacts of introducing JABs32 mutations in the genes spo0A, abrB and abh from 3NA into strain KM1016, a surfactin-forming derivative of B. subtilis 168, was investigated. This study aims to show these mutations are responsible for the surfactin producing performance of strain JABs32 in fed-batch bioreactor cultivations. Results Single and double mutant strains of B. subtilis KM1016 were constructed encoding gene deletions of spo0A, abrB and homologous abh. Furthermore, an elongated abrB version, called abrB*, as described for JABs32 was integrated. Single and combinatory mutant strains were analysed in respect of growth behaviour, native P-srfA promoter expression and surfactin production. Deletion of spo0A led to increased growth rates with lowered surfactin titers, while deletion or elongation of abrB resulted in lowered growth rates and high surfactin yields, compared to KM1016. The double mutant strains B. subtilis KM1036 and KM1020 encoding Delta spo0A abrB* and Delta spo0A Delta abrB were compared to reference strain JABs32, with KM1036 exhibiting similar production parameters and impeded cell growth and surfactin production for KM1020. Bioreactor fed-batch cultivations comparing a Delta spo0A abrB* mutant of KM1016, KM681, with JABs32 showed a decrease of 32% in surfactin concentration. Conclusions The genetic differences of B. subtilis KM1016 and JABs32 give rise to new and improved fermentation methods through high cell density processes. Deletion of the spo0A locus was shown to be the reason for higher biomass concentrations. Only in combination with an elongation of abrB was this strain able to reach high surfactin titers of 18.27 g L-1 in fed-batch cultivations. This work shows, that a B. subtilis strain can be turned into a high cell density surfactin production strain by introduction of two mutations.

Automated summary

This study investigated the impact of introducing mutations from strain JABs32 into B. subtilis KM1016 on surfactin production performance. The results showed that deletion of spo0A led to increased growth rates but lowered surfactin titers, while deletion or elongation of abrB resulted in decreased growth rates but higher surfactin yields. The genetic differences between B. subtilis KM1016 and JABs32 offer new and improved fermentation methods for high cell density processes.