Carbon and Nitrogen Cycling by Nitrospina in the Dark Ocean : A Genomic Analysis
Mathyer, Mary E.
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The dark ocean is thought to harbor chemolithoautotrophic microbes that fix inorganic carbon and use inorganic sources of energy, but the specific organisms carrying out these processes are vastly unknown. Members of the nitrite-oxidizing bacteria group Nitrospina sp. are abundant dark ocean microbes who may function as chemolithoautotrophs, as suggested by an evolutionarily related surface bacteria Nitrospina gracilis. Using single cell genomics, we obtained three Nitrospina sp. whole genome sequences. Within these sequences, I identified genes necessary for the reductive tricarboxcylic acid cycle, an inorganic carbon assimilation pathway, and the nitrite oxidation pathway, which processes inorganic energy. The Nitrospina sp. genome also contained genes that hydrolyze urea, a metabolic pathway absent in other nitrite oxidizing bacteria. Comparisons of genome sequence abundances within several ocean metagenomes revealed a global distribution of Nitrospina sp. in the dark ocean. Our molecular evidence suggests that Nitrospina sp. within the dark ocean may have a chemolithoautotrophic lifestyle, and thus play a key role in ocean carbon and nitrogen cycles.