show Abstracthide AbstractWe investigated the bacterial community structure in surface waters along a 2500 km transect in the eastern Indian Ocean, from the tropical Timor Sea to the colder temperate waters. Our data suggest that N2-fixation accounts for up to 50% of new production in this region therefore we tested whether higher N2-fixation rates are linked to a greater nitrogenase (nifH) diversity. The nifH diversity was dominated by heterotrophic Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. We did not find any mechanistic links between nifH amplicon data, bacterial richness, and primary productivity due to the overall low nifH evenness in this region.