Characterization of depth-related population variation in microbial communities of a coastal marine sediment using 16S rDNA-based approaches and quinone profiling

Depth-related changes in whole-community structure were evaluated in a coas tal marine sediment using a molecular fingerprinting method, terminal restr iction fragment length polymorphism (T-RFLP) analysis, and a chemotaxonomic technique (quinone profiling). Dendrograms derived from both T-RFLP analys is and quinone profiling indicated a significant variation in microbial com munity structure between the 0-2 cm layer and deeper layers. This correspon ded to the dramatic change in the redox potential, acid-volatile sulphide-s ulphur and bacterial numbers observed at 0-2 cm and 2-4 cm depths. A signif icant change in the number of terminal restriction fragments (T-RFs) was al so detected at this transition depth. However, the change in major T-RFs wi th depth was not seen in electropherograms. The population changes were pri marily variations in minor ribotypes. Most quinone homologues were detected at all depths, although the quinone composition changed with depth, Theref ore, quinone profiling also suggested that the depth-related variation was primarily attributable to minor bacterial groups rather than change in the major population structure. 16S rDNA clone library analysis revealed that c lones belonging to the genera Vibrio and Serratia predominated as major bac terial groups at all depths. Our data suggested that the sediment community might result from sedimentation effects of sinking particles, overall, our results demonstrated that the combined methods of T-RFLP analysis and quin one profiling were effective for assessing depth-related microbial populati ons.