RT Journal Article SR Electronic(1) A1 Starkenburg, Shawn R. A1 Arp, Daniel J. A1 Bottomley, Peter J.YR 2008 T1 d-Lactate metabolism and the obligate requirement for CO2 during growth on nitrite by the facultative lithoautotroph Nitrobacter hamburgensis JF Microbiology, VO 154 IS 8 SP 2473 OP 2481 DO https://doi.org/10.1099/mic.0.2008/018085-0 PB Microbiology Society, SN 1465-2080, AB Nitrobacter hamburgensis X14 is a facultative lithoautotroph that conserves energy from the oxidation of nitrite () and fixes carbon dioxide (CO2) as its sole source of carbon. The availability of the N. hamburgensis X14 genome sequence initiated a re-examination of its mixotrophic and organotrophic potential, as genes encoding three flavin-dependent oxidases were identified that may function to oxidize lactate, providing energy and carbon for growth. The response of N. hamburgensis to d- and l-lactate in the presence (mixotrophy) and absence (organotrophy) of was examined. l-Lactate did not support organotrophic growth or stimulate mixotrophic growth. In contrast, d-lactate enhanced the growth rate and yield of N. hamburgensis in the presence of , and served as the sole carbon and energy source for growth in the absence of with ammonium as the sole nitrogen source. Lithoautotrophically grown cells immediately consumed d-lactate, suggesting that a lactate metabolic pathway is constitutively expressed. Nevertheless, a physiological adaptation to lactate occurred, as d-lactate-grown cells consumed and assimilated lactate at a faster rate than -grown cells, and the d-lactate-dependent O2 uptake rate was significantly greater in cells grown either organotrophically or mixotrophically compared with cells grown lithoautotrophically. Although d-lactate was assimilated and metabolized to CO2 in the presence or absence of , exposure to atmospheric CO2 or the addition of 0.75 mM sodium carbonate was required for mixotrophic growth and for optimum organotrophic growth on d-lactate., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.2008/018085-0