Microbial dynamics in autotrophic and heterotrophic seawater mesocosms. II. Bacterioplankton community structure and hydrolytic enzyme activities

Abstract

A 20 d seawater mesocosm experiment was conducted to study microbial loop and carbon cycling dynamics in 3 experimental systems of different trophic status. Two mesocosms were supplemented with phytoplankton (Phaeocystis in one mesocosm and diatoms in another). This report details the variations in bacterial community composition and in carbon utilization potential investigated via assays measuring the hydrolysis of complex polysaccharides and a simple peptide compound. The first half of the study period was dominated by bacterial growth and large shifts in community composition coinciding with utilization of the organic carbon present at the beginning of the experiment, as shown by hydrolysis of specific polysaccharides and drawdown of labile dissolved organic carbon. During the second half of the experiment, bacterioplankton abundance, composition, and enzymatic activities changed in response to the experimental treatments. Multiple correlation analyses implicated co-variation between rRNA gene DGGE phylotypes (e.g. Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes) and specific combinations of environmental parameters and carbon resources, indicating phylotypic specialization to the experimental mesocosm conditions. Similarly, hydrolysis of 3 polysaccharides (xylan, chondroitin, and Isochrysis extract) correlated significantly with particular phylotypes, providing evidence of species-specific influences on carbon utilization that varied temporally over the experiment period. Aminopeptidase activity mirrored biomass accumulation, as indicated by positive correlations (> 0.80) with most biomass indicators determined. These results illustrate that combined molecular and biochemical analysis of active microbial communities can illuminate linkages between specific organisms and important ecosystem processes such as carbon utilization. Additionally, our findings show that trophic status was reflected in community composition and carbon utilization activities.

Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation

“…High levels of dissolved endopeptidase activity in coastal seawater (Obayashi and Suzuki, 2008) also underscore the importance of cell-free enzymes in the ocean. The relative contributions of cell-free enzymes to total hydrolytic activity varies among enzymes; for example, contributions of dissolved laminarinase and xylanase to total hydrolytic activities were found to vary with site and season in a riverine-marine transect (Keith and Arnosti, 2001), and varied temporally during the course of a mesocosm bloom (Murray et al, 2007).…”

Spatio-temporal patterns of bacterioplankton production and community composition related to phytoplankton composition and protistan bacterivory in a dam reservoir

“…Sundh 1992, Giroldo et al 2007). Even so, it is not known which algal species are the major EPP producers, though tight species-specific algal-bacterial relationships have been suggested for naturally occurring bacterial-algal consortia (Lindström 2001, Grossart et al 2005, Murray et al 2007.…”

“…Lindström 2001, Grossart et al 2005, Murray et al 2007). In a study of 5 mesotrophic lakes in Sweden, bacterioplankton composition was found to be significantly related to the biomass of cryptophytes and diatoms; however, the mechanisms of such algal-bacterial interactions remained unexplained (Lindström 2000(Lindström , 2001.…”

“…Sundh 1992, Giroldo et al 2007). Even so, it is not known which algal species are the major EPP producers, though tight species-specific algal-bacterial relationships have been suggested for naturally occurring bacterial-algal consortia (Lindström 2001, Grossart et al 2005, Murray et al 2007.We conducted seasonal sampling at 3 sites along the longitudinal axis of the canyon-shaped Ř ímov reservoir to test the hypothesis that spatially different bottom-up and top-down factors control bacterioplankton dynamics and community composition. Specific attention was paid to the following questions: (1) Are the autochthonously produced organic substrates, measured as EPP, a carbon source sufficient to meet bacterioplankton carbon demand in different parts of the reservoir?…”

“…Bacterial communities can specifically react to changes in the quality of utilizable compounds re-259 Aquat Microb Ecol 51: [249][250][251][252][253][254][255][256][257][258][259][260][261][262] 2008 leased as EPP, and thus e.g. different species of marine diatoms harbor distinct bacterial communities (Grossart et al 2005, Murray et al 2007.Only 2 phytoplankton groups overwhelmingly dominated the phytoplankton community (Fig. 6).…”