Nitrogenase gene expression in the Chesapeake Bay Estuary

Summary Like many estuaries, the Chesapeake Bay has pronounced gradients in salinity and nutrients. Previous studies have shown that there is a high diversity of nitrogenase ( nifH ) genes in the estuary, and that there are specific distributions of individual nifH phylotypes. In contrast to previous work that revealed the remarkable diversity of nifH phylotypes in the Chesapeake estuary, in this study of nifH expression we only detected two phylotypes, and both were phylogenetically related to cyanobacterial nifH genes. One of the phylotypes was closely related to a nifH sequence from the filamentous, heterocystous cyanobacterium Anabaena cylindrica , and was found at the head of the estuary. The other phylotype was found in a sample collected near the mouth of the estuary and was closely related to nifH sequences from Group A u