Ammonium is the preferred reduced nitrogen form many microbes use for assimilation and growth, but is often absent from offshore waters. Microorganisms can metabolize alternative organic reduced nitrogen forms if they possess genes encoding for cyanase (cynS), or urease (ureC), which catalyze the decomposition of cyanate and urea respectively. Little is known about which microbes contain these genes in the environment. We quantified the microbes that can use cyanate and/or urea in oxic and anoxic environments by using a phylogenetic read placement technique with depth profiles of metagenomes from two Pacific Ocean regions: an oxic region represented by the nutrient limited Hawaii Ocean Time series, and two Oxygen Deficient Zone (ODZ) environments represented by the Eastern Tropical South and the North Pacific.  Ammonia-oxidizing Thaumarchaeota all had the ability to use urea in deep oxic waters. Contrastingly, ~40% of heterotrophic SAR11 bacteria had the ureC gene in surface water where nitrate was undetectable, but none did in deep waters. In ODZs, N₂ producing anammox bacteria all contained genes to use cyanate, but 50-70% had genes to use urea. Contrastingly, all Thioglobaceae had the ability of using urea in the ODZ, but few did in oxic waters. Nitrite-oxidizing Nitrospina all had genes to use urea with ~35% having genes to use cyanate in the lower euphotic zone, but not below. This structuring of who can utilize which reduced nitrogen form could both reflect competition between microbes and substrate availability.  

Primary Presenter: Paulina Alejandra Huanca Valenzuela, UMCES (phuanca@umces.edu)

Authors:

Jacob Cram, University of Maryland Center for Environmental Science (UMCES)  (jcram@umces.edu)

Clara Fuchsman, University of Maryland Center for Environmental Science (UMCES)  (cfuchsman@umces.edu)