Genotypic Diversity Within a Natural Coastal Bacterioplankton Population

Abstract

The genomic diversity and relative importance of distinct genotypes within natural bacterial populations have remained largely unknown. Here, we analyze the diversity and annual dynamics of a group of coastal bacterioplankton (greater than 99% 16 S ribosomal RNA identity to Vibrio splendidus ). We show that this group consists of at least a thousand distinct genotypes, each occurring at extremely low environmental concentrations (on average less than one cell per milliliter). Overall, the genomes show extensive allelic diversity and size variation. Individual genotypes rarely recurred in samples, and allelic distribution did not show spatial or temporal substructure. Ecological considerations suggest that much genotypic and possibly phenotypic variation within natural populations should be considered neutral.

Low Intraspecific Diversity in a Polynucleobacter Subcluster Population Numerically Dominating Bacterioplankton of a Freshwater Pond

“…Only a few studies have revealed the microdiversity of free-living bacterial populations (1,29,42,45). The investigated PnecC population differed from these populations in a low microdiversity and a strongly uneven population structure.…”

“…Recently, Acinas et al (1) demonstrated by the construction and analysis of 16S rRNA clone libraries that a coastal bacterioplankton community contained a very high diversity of ribotypes, the vast majority of which fell into phylogenetically microdiverse sequence clusters (Ͻ1% divergent 16S rRNA sequences). Similarly, extensive microdiversities were also observed in populations of sulfate-reducing bacteria inhabiting a salt marsh (29) and in a Vibrio splendidus population from coastal bacterioplankton (42). The V. splendidus population consisted of at least a thousand distinct genotypes, which demonstrated a high variability in genome size and allelic composition (42).…”

“…Similarly, extensive microdiversities were also observed in populations of sulfate-reducing bacteria inhabiting a salt marsh (29) and in a Vibrio splendidus population from coastal bacterioplankton (42). The V. splendidus population consisted of at least a thousand distinct genotypes, which demonstrated a high variability in genome size and allelic composition (42).…”

“…The monophyletic PnecC cluster is characterized by a high minimum sequence similarity of 98.5% (23) and resembles in this feature the microdiverse clusters of marine bacteria (1,42). Sequences affiliated with PnecC were previously obtained from endosymbionts of aquatic ciliates (40,44), from many freshwater habitats investigated with culture-independent methods (11,21,27,50), and from strains isolated from several freshwater habitats (23).…”

Molecular eco-systems biology: towards an understanding of community function

“…Previous studies have detected variation in species composition in various habitats, both spatially (reviewed, for example, in Refs [35,[63][64][65]) and temporally (for example, Refs [66,67]). Spatio-temporal variation has been linked to variation in environmental conditions [35,68], even to the point at which environmental parameters can be predictive of species composition [55].…”