Thalassolituus haligoni sp. nov., BB40, a model species for non-cyanobacterial diazotrophs within Oceanospirillales isolated from a Fjord-like Inlet in Kjipuktuk

Abstract Marine non-cyanobacterial diazotrophs (NCDs) are recognized as globally distributed, however, few representatives have been isolated in pure cultures. As a result, understanding the physiology, growth rate, substrate preference and dinitrogen (N 2 ) fixation capabilities proves difficult. Thalassolituus haligoni . sp. nov., BB40 was isolated from a fjord-like inlet within Kjipuktuk (Halifax), Nova Scotia. The fully sequenced genome displayed all necessary genes required for N 2 fixation, and various carbon uptake pathways. The gram-negative flagellated rod shape bacterium displayed significantly higher growth rates in medium amended with nitrate (NO 3 - ) or ammonia (NH 3 ), compared to dissolved N 2 , as the sole nitrogen source. Biological N 2 fixation rates were detectable across all conditions, measuring a range from 9.34 × 10 -6 to 1.4 × 10 -1 fmol N cell -1 day -1 . Growth of the isolate was successful between 4 °C up to 35 °C, with a T opt of 20 °C for N 2 , and between 27 - 30 °C for fixed nitrogen (NO 3 - and NH 3 ). The closest relatives to T. haligoni , were found to be the uncultured Arc-gamma-03 (99% average nucleotide identity (ANI)) and Oceanobacter antarcticus (81% ANI). T. haligoni also displays versatile capabilities for growth on various carbon, and nitrogen sources, and antibiotics. Collectively this study provides an in-depth physiological assessment of an Oceanospirillales diazotrophic species which we presently have limited knowledge of.