Phenotypic variation in Azospirillum brasilense exposed to starvation

Abstract

Bacteria have developed mechanisms that allow them maintaining cell viability during starvation and resuming growth when nutrients become available. Among these mechanisms are adaptive mutations and phase variation, which are often associated with DNA rearrangements. Azospirillum brasilense is a Gram-negative, nitrogen-fixing, plant growth-promoting rhizobacterium. Here we report phenotypic variants of A. brasilense that were collected after exposure to prolonged starvation or after re-isolation from maize roots. The variants differed in several features from the parental strains, including pigmentation, aggregation ability, EPS amount and composition and LPS structure. One of the phenotypic variants, overproducing EPS and showing an altered LPS structure, was further characterized and showed differential response to several stresses and antibiotics relative to its parental strain. Characterization of the variants by repetitive-PCR revealed that phenotypic variation was often associated with DNA rearrangements.

Phenotypic Variation in the Plant Pathogenic Bacterium Acidovorax citrulli

“…Phenotypic variation is often associated with large DNA rearrangements and PVs can be distinguished from their parental strains by diverse DNA fingerprinting methods [13,39–41]. Here we showed that 7a1 PVs slightly differed from the parental strain in their PFGE profile following restriction with XbaI and variant 7a1V2 slightly differed from the parental strain (and from variant 7a1V1) in REP-PCR.…”

“…In such cases, PVs can be distinguished from their parental strains by DNA fingerprinting methods [13,39–41]. We assessed whether variants M6V1 and M6V2 as well as 7a1V1 and 7a1V2 differ from their corresponding parental strains, in pulse field gel electrophoresis (PFGE) and repetitive-PCR (rep-PCR) profiles.…”

“…Phenotypic variation is a well-recognized phenomenon in plant-associated Gram-negative bacterium [13,41–45]. Essentially, it is an adaptive mechanism that may lead to increased fitness and survival of an organism, depending upon its ability to colonize, persist and spread around the environment.…”

“…In addition, SEM analyses showed that variant cells of both strains possessed a slightly increased roughness than parental type cells (Figure S1). These morphological alterations could be result of changes in surface-exposed moieties such as fimbriae/pili, lipopolysaccharide (LPS) and extracellular polysaccharides, as shown for other bacteria [8,11,41,42,47–49]. Although this question should be further investigated in future studies, here we show that under tested conditions, the characterized variants of strains M6 and 7a1 lacked the ability to produce type IV pili (T4P), which could contribute to these morphological alterations (Figure 6).…”

Phenotypic variation in Acidovorax radicisN35 influences plant growth promotion

“…Various DNA regulatory mechanisms are involved in phenotypic variation: site specific inversion, recombinational deletion, transposition, spontaneous duplication and mutation, slipped-strand mispairing, genomic rearrangement, and differential methylation. Phenotypic variation affects root colonization, biocontrol activity, aggregation, exopolysaccharide production, lipopolysaccharide production, exoenzyme production, and secondary metabolite production (Katupitiya et al, 1995;van den Broek et al, 2005;Vial et al, 2006;Wisniewski-Dyé & Vial, 2008;Lerner et al, 2010). In addition, according to van der Woude & Baumler (2004), changes in global regulatory protein expression can lead to an alteration in the expression of several operons, thus resulting in phenotypic variation.…”