Nitrate assimilation genes of the marine diazotrophic, filamentous cyanobacterium Trichodesmium sp strain WH9601

A 4.0-kb DNA fragment of Trichodesmium sp. strain WH9601 contained gene seq uences encoding the nitrate reduction enzymes, nirA and narB. A third gene positioned between nirA and narB encodes a putative membrane protein with s imilarity to the nitrate permeases of Bacillus subtilis (NasA) and Emericel la nidulans (CrnA). The gene was shown to functionally complement a Delta n asA mutant of B. subtilis and was assigned the name napA (nitrate permease) . NapA was involved in both nitrate and nitrite uptake by the complemented B. subtilis cells. napA is distinct from the nrt genes that encode the nitr ate transporter of freshwater cyanobacteria.