Adaptive divergence in experimental populations of Pseudomonas fluorescens. I. Genetic and phenotypic bases of wrinkly spreader fitness.
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.
Spiers
Andrew J
AJ
Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom.
Kahn
Sophie G
SG
Bohannon
John
J
Travisano
Michael
M
Rainey
Paul B
PB
D000222:Adaptation, Physiological; D019143:Evolution, Molecular; D005838:Genotype; D010641:Phenotype; D020161:Physical Chromosome Mapping; D011551:Pseudomonas fluorescens / Q000235:genetics*; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic / Q000502:physiology