Temporal fluctuations in the pseudomonad population associated with sugar beet leaves

Abstract

A total of 473 fluorescent pseudomonads were isolated from sugar beet leaves, sampled approximately every 30–40 days, over three consecutive growing seasons. Total cellular fatty acid composition and restriction fragment length polymorphism data for the flanking regions of the ribosomal RNA operon were obtained for each isolate to assess the temporal variability in diversity of leaf-associated fluorescent pseudomonad populations. A total of 115 distinct ribotypes (genotypes) were detected within the cluster identified by principal component analysis of cellular fatty acid content. Although the abundance of isolates was lognormally distributed, individual ribotypes were detected more often than would be predicted by such a distribution. The number of ribotypes identified in each sample was directly related to the size of that sample. Despite the implication that the sample size was too small, the data suggested that some individual ribotypes were capable of long-term survival and that there was a dynamic, non-random and continuous turnover within the population. A seasonal pattern of isolate reoccurrence was observed. As one group suffered decline, the next group, better adapted to the prevailing conditions, proliferated.