Adaptive Divergence in Experimental Populations ofPseudomonas fluorescens. I. Genetic and Phenotypic Bases of Wrinkly Spreader Fitness

Abstract

A central feature of all adaptive radiations is morphological divergence, but the phenotypic innovations that are responsible are rarely known. When selected in a spatially structured environment, populations of the bacterium Pseudomonas fluorescens rapidly diverge. Among the divergent morphs is a mutant type termed “wrinkly spreader” (WS) that colonizes a new niche through the formation of self-supporting biofilms. Loci contributing to the primary phenotypic innovation were sought by screening a WS transposon library for niche-defective (WS-) mutants. Detailed analysis of one group of mutants revealed an operon of 10 genes encoding enzymes necessary to produce a cellulose-like polymer (CLP). WS genotypes overproduce CLP and overproduction of the polymer is necessary for the distinctive morphology of WS colonies; it is also required for biofilm formation and to maximize fitness in spatially structured microcosms, but overproduction of CLP alone is not sufficient to cause WS. A working model predicts that modification of cell cycle control of CLP production is an important determinant of the phenotypic innovation. Analysis of >30 kb of DNA encoding traits required for expression of the WS phenotype, including a regulatory locus, has not revealed the mutational causes, indicating a complex genotype-phenotype map.

Evolutionary flexibility in routes to mat formation by Pseudomonas

“…However, the downstream targets of c‐di‐GMP differ in the two backgrounds. In SBW25, elevated c‐di‐GMP stimulates cellulose production by the Wss biosynthetic machinery (Gal et al., 2003; Goymer et al., 2006; Spiers et al., 2002). PICF7 lacks wss homologues, and cannot synthesize cellulose.…”

Adaptation and phenotypic diversification of Bacillus thuringiensis biofilm are accompanied by fuzzy spreader morphotypes

“…Like wrinkly-spreader, fuzzy-spreader displays a multicellular phenotype including increased biofilm formation ability 72 . However, the selective advantage of the fuzzy-spreader morph was not clarified while the wrinkly-spreader was comprehensibly examined by Rainey group 36 , 91 – 93 . These studies laid a foundation for subsequent phenotypic and genotypic characterization of fuzzy-spreader 19 , demonstrating that fuzzy-spreader follows an ecological cycle of forming cellular rafts, collapsing into the bottom of the vial and reforming the rafts in the microcosms, which displays analogy to the repetitive life cycle of FS morphotype in this study.…”

Interspecific Niche Competition Increases Morphological Diversity in Multi-Species Microbial Communities

“…WS density was highly variable in the presence of O and A, and this may be explained by the advantage of forming biofilms and historical contingences. The diversified WS is a cooperating group that can enable individuals to align with them by overproducing an adhesive polymer and promote the colonization of the air-liquid interface though the overproduction is costly to individuals (Spiers et al, 2002;Rainey and Rainey, 2003). Therefore, if mutations to form WS arose late in a population or P. fluorescens initially grew slowly, WS may lose the chance to spread because the available niche is already partially occupied by competitor species.…”

“…The relative short-term evolution limited the study to further investigate more nuanced processes such as how within-species diversification feedback to affect community structure. Though the three morphotypes of P. fluorescens has been widely used for diversity estimation, less consideration has been given to its genetic diversity (Spiers et al, 2002;Fukami et al, 2007).…”