Enzymatic Activity, Bacterial Distribution, and Organic Matter Composition in Sediments of the Ross Sea (Antarctica)

• Published in: Applied and Environmental Microbiology
• Main Authors: Fabiano, Mauro, Danovaro, Roberto
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 1998
• Subjects: Antarc*; Antarctic; Antarctica; Arctic; Ross Sea
• Online Access: http://dx.doi.org/10.1128/aem.64.10.3838-3845.1998; https://journals.asm.org/doi/pdf/10.1128/AEM.64.10.3838-3845.1998

ABSTRACT Enzymatic activities of aminopeptidase and β-glucosidase were investigated in Antarctic Ross Sea sediments at two sites (sites B and C, 567 and 439 m deep, respectively). The sites differed in trophic conditions related to organic matter (OM) composition and bacterial distribution. Carbohydrate concentrations at site B were about double those at site C, while protein and lipid levels were 10 times higher. Proteins were mainly found in a soluble fraction (>90%). Chloropigment content was generally low and phaeopigments were almost absent, indicating the presence of reduced inputs of primary organic matter. ATP concentrations (as a measure of the living microbial biomass) were significantly higher at site B. By contrast, benthic bacterial densities at site C were about double those at site B. Bacterial parameters do not appear to be “bottom-up controlled” by the amount of available food but rather “top-down controlled” by meiofauna predatory pressure, which was significantly higher at site B. Aminopeptidase and β-glucosidase extracellular enzyme activities (EEA) in Antarctic sediments appear to be high and comparable to those reported for temperate or Arctic sediments and characterized by low aminopeptidase/β-glucosidase ratios (about 10). Activity profiles showed decreasing patterns with increasing sediment depth, indicating vertical shifts in both availability and nutritional quality of degradable OM. Vertical profiles of aminopeptidase activity were related to a decrease in protein concentration and/or to an increase in the insoluble refractory proteinaceous fraction. The highest aminopeptidase activity rates were observed at site C, characterized by much lower protein concentrations. Differences in EEA between sites do not seem to be explained by differences in the in situ temperature (−1.6 and −0.8°C at sites B and C, respectively). Aminopeptidase activity profiles are consistent with the bacterial biomass and frequency of dividing cells. Enzyme substrate affinity was generally dependent upon ...