ABSTRACT: We demonstrated that bacterioplankton utilization of N-containing substrates, in relation to overall substrate utilization, can be assessed by calculating a nitrogen use (NUSE) index from Biolog-ECO microplate readings. The NUSE index was positively correlated with bacterial-specific aminopeptidase activity in coastal plankton samples, and it decreased after ammonia or amino acid addition to seawater cultures; this indicated that the index was sensitive to changes in N concentrations in natural samples. The index provides valuable information on dissolved organic nitrogen processing by natural bacterial assemblages, and thereby substantially expands the utility of the Biolog-ECO microplates.
KEY WORDS: Biolog · Bacterioplankton · Substrate utilization · Dissolved organic nitrogen · DON · Nutrients · Amino acids
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