Abstract
Nitrogen (N) is a key nutrient limiting primary production; hence, knowledge about sources of nitrogen is a prerequisite for controlling productivity of the Baltic Sea. Fixation of gaseous N (N2) from the atmosphere by bacteria supplies a significant portion of the N used for primary production. Cyanobacteria are regarded as the main N2-fixing organisms in the Baltic, but recent research suggests that heterotrophic bacteria also play a role in planktonic N2-fixation. This project focuses on the identity, distribution, and activity of those bacteria and involves sampling during cruises in the Baltic Sea and laboratory experiments to elucidate mechanisms affecting N2-fixation. Clone libraries of the so-called nifH gene will provide information about heterotrophic bacteria having the genetic potential for N2-fixation and about those that actually express the gene. Specific bacteria will be quantified in Baltic seawater using PCR to examine their distribution relative to environmental variables. Heterotrophic N2-fixing bacteria will be cultivated in semi-solid N deficient medium with a vertical O2 gradient and in N deficient medium by dilution-to-extinction. Obtained isolates will be sequenced (nifH and 16S rDNA) and effects of O2 and reduced N on their N2-fixation will be examined. The project provides information about the diversity and distribution of heterotrophic N2-fixing bacteria in the Baltic Sea and gains insights into some of the factors regulating their N2-fixation.
Sweden