Functional diversity of bacterioplankton assemblages in western Antarctic seawaters during late spring

Abstract

Functional diversity and aminopeptidase activity (AMA) in bacterial assemblages were determined in western Antarctic waters during late spring 2002. Functional diversity was assayed by the patterns of sole carbon source utilization in Biolog-ECO Microplates TM and AMA with the fluorogenic substrate leucine 7-amido-4-methylcoumarin. N-acetyl-D-glucosamine and D-cellobiose were the most used carbohydrates. This suggested that used dissolved organic carbon (DOC) was mostly of either zoo-or phytoplankton origin. Principal component analysis of the sole carbon source utilization profiles separated the samples according to salinity and temperature. This separation corresponded roughly with the 3 areas of study: Bransfield Strait (BR), Gerlache Strait (GE) and Bellingshausen Sea (BE). AMA was higher in the upper 40 m, probably associated with the higher organic matter load. Phytoplankton biomass was the factor that accounted for the highest variance in AMA, but did not have a clear influence on functional diversity of bacterioplankton. Our findings indicate that differences in functional diversity of bacterioplankton populations in western Antarctic waters are not directly related to phytoplanktonic abundance. This suggests that bacteria could utilize other carbon sources than DOC freshly released by phytoplankton. KEY WORDS: Bacterial activity · Functional diversity · Biolog · Aminopeptidase · Ectoenzyme · Antarctica Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 292: [13][14][15][16][17][18][19][20][21] 2005 autotrophic production than consumption (Misic et al. 2002).Composition of the organic matter utilized by the bacterial populations is likely to be an important regulator of the metabolic activity of bacterioplankton. Biolog Microplates TM have provided an insight into the functional diversity of bacterial populations in many ecosystems (reviewed by Preston-Mafham et al. 2002). In marine environments the Biolog approach has distinguished bacterial populations according to their metabolic capabilities depending on the origin of the organic matter available in the Californian coast (Hollibaugh 1994).The distribution of bacterioplankton biomass and production in western Antarctica is relatively well known (Karl et al. 1996, and this allows studies of functional diversity of bacterioplankton that have not been investigated until now. We determined bacterial AMA and bacterial utilization of carbon sources in Biolog-ECO plates. We then proposed the following hypothesis: Since DOC in Antarctic waters derives mainly from primary production, we expect (1) a relationship between chl a concentration and AMA; and (2) a key role of phytoplankton biomass in determining functional bacterial diversity according to the sole carbon source utilization patterns in the Biolog-ECO plates. MATERIALS AND METHODSSituation and sampling strategy. Samples were collected during the TEMPANO cruise on board of RV 'BIO-Hespérides', from 30 November to 16 December 2002. The area of st...

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