Changes of Diversity Pattern of Proteolytic Bacteria over Time and Space in an Agricultural Soil

The genetic heterogeneity of neutral metalloprotease (npr) gene fragments from soil proteolytic bacteria was investigated at a cultivated field site with four different soil types and at three different depths in April, July, and October. Terminal restriction fragment length polymorphism (T-RFLP) analyses of polymerase chain reaction-amplified npr gene fragments were applied to study the dynamic of the npr gene pool with regard to environmental conditions. The aim of this study was to relate differences in npr community structure and richness to the vertical, site, and seasonal variations naturally occurring at the field site under investigation. T-RFLP analysis revealed a noticeable seasonal variability in the community structure of npr-containing bacteria. The data suggest that the composition of the npr proteolytic bacterial population in July differed from those at the other dates. Additionally, the diversity of npr genes decreased with increasing soil depth revealing the highest values in upper layers. The reasons behind the observed patterns in the community structure might be mainly seasonal and vertical variation of the quantity and heterogeneity of available substrates as well as spatial isolation caused by a varying water amount and the connectivity of soil particles among the soil profile. Sequencing and phylogenetical analysis of 120 npr clones from the top soils collected in July revealed that most of the clones exhibit only poor homology to npr genes of isolates previously obtained from various environments, indicating the presence of until now uncharacterized npr coding proteolytic bacteria at the study site.