Environmentally triggered genomic plasticity and capsular polysaccharide formation are involved in increased ethanol and acetic acid tolerance in Kozakia baliensis NBRC 16680

Abstract

BackgroundKozakia baliensis NBRC 16680 secretes a gum-cluster derived heteropolysaccharide and forms a surface pellicle composed of polysaccharides during static cultivation. Furthermore, this strain exhibits two colony types on agar plates; smooth wild-type (S) and rough mutant colonies (R). This switch is caused by a spontaneous transposon insertion into the gumD gene of the gum-cluster, resulting in a heteropolysaccharide secretion deficient, rough phenotype. To elucidate, whether this is a directed switch triggered by environmental factors, we checked the number of R and S colonies under different growth conditions including ethanol and acetic acid supplementation. Furthermore, we investigated the tolerance of R and S strains against ethanol and acetic acid in shaking and static growth experiments. To get new insights into the composition and function of the pellicle polysaccharide, the polE gene of the R strain was additionally deleted, as it was reported to be involved in pellicle formation in other acetic acid bacteria.ResultsThe number of R colonies was significantly increased upon growth on acetic acid and especially ethanol. The morphological change from K. baliensis NBRC 16680 S to R strain was accompanied by changes in the sugar contents of the produced pellicle EPS. The R:ΔpolE mutant strain was not able to form a regular pellicle anymore, but secreted an EPS into the medium, which exhibited a similar sugar monomer composition as the pellicle polysaccharide isolated from the R strain. The R strain had a markedly increased tolerance towards acetic acid and ethanol compared to the other NBRC 16680 strains (S, R:ΔpolE). A relatively high intrinsic acetic acid tolerance was also observable for K. baliensis DSM 14400T, which might indicate diverse adaptation mechanisms of different K. baliensis strains in altering natural habitats.ConclusionThe results suggest that the genetically triggered R phenotype formation is directly related to increased acetic acid and ethanol tolerance. The polE gene turned out to be involved in the formation of a cell-associated, capsular polysaccharide, which seems to be essential for increased ethanol/acetic tolerance in contrast to the secreted gum-cluster derived heteropolysaccharide. The genetic and morphological switch could represent an adaptive evolutionary step during the development of K. baliensis NBRC 16680 in course of changing environmental conditions.