Spatial and temporal variation of phenanthrene-degrading bacteria in intertidal sediments

Abstract

Phenanthrene-degrading bacteria were isolated from a 1-m2 intertidal sediment site in Boston Harbor. Samples were taken six times over 2 years. A total of 432 bacteria were isolated and characterized by biochemical testing. When clustered on the basis of phenotypic characteristics, the isolates could be separated into 68 groups at a similarity level of approximately 70%. Several groups (a total of 200 isolates) corresponded to well-characterized species belonging the genera Vibrio and Pseudomonas. Only 51 of the 437 isolates (< 11.7% of the total) hybridized to a DNA probe that encodes the upper pathway of naphthalene and phenanthrene degradation in Pseudomonas putida NCIB 9816. A cluster analysis indicated that the species composition of the phenanthrene-degrading community changed significantly from sampling date to sampling date. At one sampling time, 12 6-mm-diameter core subsamples were taken within the 1-m2 site to determine the spatial variability of the degrading communities. An analysis of molecular variance, performed with the phenotypic characteristics, indicated that only 6% of the variation occurred among the 12 subsamples, suggesting that the subsamples were almost identical in composition. We concluded that the communities of phenanthrene-degrading bacteria in the sediments are very diverse, that the community structure undergoes significant change with time but does not vary significantly on a spatial scale of centimeters, and that the predominant genes that encode phenanthrene degradation in the communities are not well-characterized.

FIG. 1

Phenotypic similarities between isolates. Levels of similarity were calculated by using Jaccard’s index, and clustering was by the UPGMA method. At a similarity level of 70%, 83 taxonomic units were present. Taxonomic units containing three or more strains are numbered, and the presumptive identity of each, if known, is indicated.

FIG. 2

Relative changes in species compositions of degrader communities.

FIG. 3

Dendrogram showing the relationships among the phenanthrene-degrading communities. The analysis was performed by determining how many isolates belonging to each of the 83 taxa were present in each community. Communities are identified by sampling date and subsample number.