Impact of particulate organic matter composition and degradation state on the vertical structure of particle-associated and planktonic lacustrine bacteria

Abstract

In order to determine how concentration, composition, and degradation states of par- ticulate organic matter (POM) influence lacustrine bacteria, we analyzed changes in bacterial community (BC) structure and total bacterial cell abundance throughout the water columns of 2 contrasting deep lakes in Switzerland. Lake Brienz is oligotrophic and fully oxic while Lake Zug is eutrophic and partially anoxic. The community composition of the particle-associated (>5 µm) and free-living (>0.2, <5 µm) bacteria was analyzed by automated ribosomal intergenic spacer analysis (ARISA). Cluster analysis showed that the lakes comprised distinct BCs. However, the BCs of both lakes were structured with depth. Although particulate amino compounds appeared to impact the number of ARISA-operational taxonomic units of the particle-associated BCs throug hout the lake water columns, the compositional dynamics of this bacterial fraction were affected more strongly by the sampling date and physico-chemical parameters, such as pH. For the free-living BCs, the chlorin index (CI), an indicator for the degradation state of primary produced POM, appeared to significantly impact the vertical community shifts. The vertical changes of the total bacterial cell abundance were also significantly determined by the CI and by shifts in particulate amino com- pounds. The present study shows that not only bulk environmental parameters but also POM composition and degradation state shape the abundance and composition of lacustrine BCs.