Influence of nitrate-storing sulfur bacteria on the nitrogen and phosphorus cycle of the ocean

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Nitrate-storing sulfur bacteria are abundant in most marine sediments containing free hydrogen sulfide and may reach very high biomasses. Apart from their importance for the oxidative part of the marine sulfur cycle they also interfere with the nitrogen cycle of the sediment. Until now there are indications for three different ways in which sulfur bacteria may change the total nitrogen budget of their habitats: denitrification, dissimilatory reduction of nitrate to ammonia and possibly even nitrogen fixation. Under certain conditions they may also produce significant amounts of nitrous oxide, which is a green house gas. The first goal of this project is to investigate under which conditions each of these processes occur. Preliminary studies have also shown that all nitrate-storing sulfur bacteria investigated so far contain high amounts of internally stored polyphosphate. This finding indicates that this group of bacteria may also have great influence on the phosphorus cycle of the ocean, especially as they occur in very high biomasses in some areas where recent phosphorite genesis is found. Therefore, the second focus of this project is to carry out physiological experiments and field investigations concerning the accumulation and release of polyphosphate.