Planktonic organisms that fix atmospheric nitrogen (diazotrophs) have a critical role in oceanic production and in the marine nitrogen cycle [1]. Abundance and growth rates of such organisms depend on their ability to assimilate various sources of nitrogen [2]. The availability of fixed nitrogen (such as nitrate and ammonium) can limit the productivity of the sea [3]. Diatom-diazotroph associations (DDAs) are widely reported in oligotrophic waters and have the capacity to form episodic, largely monospecific blooms that exhibit very high rates of carbon and nitrogen fixation worldwide [4–7]. Annually, Trichodesmium contributes 1– 5mmolNm−2 d−1; while diazotrophic diatoms, contribute 0.4–2.4mmolNm−2 d−1, which forms one quarter of the total input of nitrogen to the sea [8]. Globally, DDAs fix 4.79 TgNy−1 [9], which forms almost 25% of total input of nitrogen to the sea