%A Stein,Lisa %A Campbell,Mark %A Klotz,Martin %D 2013 %J Frontiers in Microbiology %C %F %G English %K Nitrosococcus,ammonia-oxidizing bacteria,ammonium,Hydroxylamine,redox,signaling,global gene expression,Microarray %Q %R 10.3389/fmicb.2013.00277 %W %L %M %P %7 %8 2013-September-13 %9 Original Research %+ Dr Lisa Stein,University of Alberta,Biological Sciences Faculty of Science,CW 405 Bio Sci Centre,Edmonton, AB,T6G 2E9,Canada,lisa.stein@ualberta.ca %+ Dr Martin Klotz,University of North Carolina, Charlotte,Biology,9201 University City Blvd,Charlotte,28223,North Carolina,United States,martin.g.klotz@gmail.com %# %! Comparative transcriptomics of Nitrosococcus oceani %* %< %T Energy-mediated vs. ammonium-regulated gene expression in the obligate ammonia-oxidizing bacterium, Nitrosococcus oceani %U https://www.frontiersin.org/articles/10.3389/fmicb.2013.00277 %V 4 %0 JOURNAL ARTICLE %@ 1664-302X %X Ammonia serves as the source of energy and reductant and as a signaling molecule that regulates gene expression in obligate ammonia-oxidizing chemolithotrophic microorganisms. The gammaproteobacterium, Nitrosococcus oceani, was the first obligate ammonia-oxidizer isolated from seawater and is one of the model systems for ammonia chemolithotrophy. We compared global transcriptional responses to ammonium and the catabolic intermediate, hydroxylamine, in ammonium-starved and non-starved cultures of N. oceani to discriminate transcriptional effects of ammonium from a change in overall energy and redox status upon catabolite availability. The most highly expressed genes from ammonium- or hydroxylamine-treated relative to starved cells are implicated in catabolic electron flow, carbon fixation, nitrogen assimilation, ribosome structure and stress tolerance. Catabolic inventory-encoding genes, including electron flow-terminating Complexes IV, FoF1 ATPase, transporters, and transcriptional regulators were among the most highly expressed genes in cells exposed only to ammonium relative to starved cells, although the differences compared to steady-state transcript levels were less pronounced. Reduction in steady-state mRNA levels from hydroxylamine-treated relative to starved-cells were less than five-fold. In contrast, several transcripts from ammonium-treated relative to starved cells were significantly less abundant including those for forward Complex I and a gene cluster of cytochrome c encoding proteins. Identified uneven steady-state transcript levels of co-expressed clustered genes support previously reported differential regulation at the levels of transcription and transcript stability. Our results differentiated between rapid regulation of core genes upon a change in cellular redox status vs. those responsive to ammonium as a signaling molecule in N. oceani, both confirming and extending our knowledge of metabolic modules involved in ammonia chemolithotrophy.