A native conjugative plasmid confers potential selective advantages to plant growth-promoting Bacillus velezensis strain GH1-13

Abstract

The conjugative plasmid (pBV71) possibly confers a selective advantage to Bacillus velezensis strain GH1-13, although a selective marker gene is yet to be identified. Here we show that few non-mucoid wild-type GH1-13 cells are spontaneously converted to mucoid variants with or without the loss of pBV71. Mucoid phenotypes, which contain or lack the plasmid, become sensitive to bacitracin, gramicidin, selenite, and tellurite. Using the differences in antibiotic resistance and phenotype, we isolated a reverse complement (COM) and a transconjugant of strain FZB42 with the native pBV71. Transformed COM and FZB42p cells were similar to the wild-type strain GH1-13 with high antibiotic resistance and slow growth rates on lactose compared to those of mucoid phenotypes. RT-PCR analysis revealed that the expression of plasmid-encoded orphan aspartate phosphatase (pRapD) was coordinated with a new quorum-sensing (QS) cassette of RapF2–PhrF2 present in the chromosome of strain GH1-13, but not in strain FZB42. Multi-omics analysis on wild-type and plasmid-cured cells of strain GH1-13 suggested that the conjugative plasmid expression has a crucial role in induction of early envelope stress response that promotes cell morphogenesis, biofilm formation, catabolite repression, and biosynthesis of extracellular-matrix components and antibiotics for protection of host cell during exponential phase.