Diversification ofPseudomonas corrugata2140 produces new phenotypes altered in GC-FAME, BIOLOG, and in vitro inhibition profiles and taxonomic identification

Abstract

Bacteria are known to rapidly produce new phenotypes, but it is unclear how phenotype "plasticity" relates to studies on the population ecology of bacteria in complex environments. We characterised a collection of 14 spontaneous phenotype variants, derived from in vitro and in vivo cultures (wheat roots) of Pseudomonas corrugata 2140, using fatty acid methyl ester profiles (GC-FAME), carbon substrate utilisation (BIOLOG), and in vitro inhibition against seven soil microorganisms. All three phenotype profiles indicated marked differences between some variants and the parent isolate. Some variant types were classified taxonomically by GC-FAME as different species to their wild-type parent, and up to a Euclidian distance of 11 from their parent. Taxonomic identification by the BIOLOG assay was more consistent; however, use of 22 carbon sources were altered (lost or gained) in one or more variants. All variant types had a reduced ability to inhibit one or more test organisms, depending on the variant and test organism. Hierarchical cluster analysis of variants using GC-FAME, BIOLOG, and inhibition profiles produced different groupings. The ability of variants to cross taxonomic boundaries specified by the GC-FAME and BIOLOG libraries at the species level has implications for both taxonomy and the ecological study of bacterial communities.

Pseudomonas corrugata: plant pathogen and/or biological resource?

“…The occurrence of pleiotropic mutants after subculturing or re‐isolation from soil, in which conversion of colony morphology from rough to smooth is associated with loss of exoenzyme activity, modification of antagonistic activity and reduction of virulence (Barnett et al ., 1999; Gustine et al ., 1995; Siverio et al ., 1996), suggests that, like the other pseudomonads, the global GacA/GacS two‐component system plays an important role in gene regulation (de Souza et al ., 2003).…”

“…In such mutants, fatty acid profiles, enzymatic activity (i.e. inability to hydrolyse casein, gelatine, lecithin and Tween 80) and carbon source assimilation varied from the parent strains (Barnett et al, 1999;Lukezic, 1979;Siverio et al, 1993Siverio et al, , 1996. Intraspecific variability and appearance of mutants call for great care when using automated identification systems, such as those based on nutritional profiles or gas chromatographic analysis of FAMEs.…”

“…P. corrugata strain 2140 isolated from wheat field soil (and its derivatives) was reported to colonize wheat roots after application on the seeds (Ryder and Borret, 1991), reduce take-all disease of wheat by G. graminis var. tritici (Barnett et al, 1998;Ross et al, 2000;Ryder and Rovira, 1993;Ryder et al, 1999;Schmidt et al, 1997) and Pythium root rot in sugarbeet (Schmidt et al, 2004). The movement and colonization of wheat roots is enhanced by the presence of earthworms (Schimdt et al, 1997).…”