Influence of nitrate availability on the distribution and abundance ofheterotrophic bacterial nitrate assimilation genes in the Barents Seaduring summer

摘要

In a transect across Norwegian coastal waters and the Barents Sea to approximately 78 degree N, distinct patterns in the distribution and abundance of bacterial assimilatory nitrate reductase (nasA) genes were observed in relation to NO super(-) sub(3) availability and bacterial dissolved inorganic nitrogen utilization. A real-time PCR assay, developed for a group of nasA genes characteristic of Marinobacter sp., which are a common group of nitrate-assimilating bacteria in the marine environment, indicated that the nasA gene abundance of Marinobacter sp. was positively correlated with NO super(-) sub(3) concentration. At 5 stations sampled, Marinobacter sp. nasA gene abundance was, on average, 8-fold higher at 80 m compared to 5 m depth, relative to total bacteria. Bacterial productivity, bacterial biomass, chlorophyll a, NH super(+) sub(4), and NO super(-) sub(3) were modeled as independent variables in a partial least-squares regression model to determine how well each variable predicted the variation in nasA community structure, defined by terminal restriction-length-fragment polymorphism analysis. NO super(-) sub(3) concentration was the best predictor, by a factor of 10, of the variability associated with nasA community structure. In a companion study of super(15)NO super(-) sub(3) and super(15)NH super(+) sub(4) uptake across the same transect, conducted at the same time as this study, bacteria were relatively more important in terms of total community uptake in the marginal ice zone, where NO super(-) sub(3) levels were high, compared to samples from the North Atlantic, where NO super(-) sub(3) concentrations were lower. Results presented here indicate that NO super(-) sub(3) availability and patterns of NO super(-) sub(3) utilization are correlated with nasA community structure variability and abundance.