title: D-Lactate metabolism and the obligate requirement for CO2 during growth on nitrite by the facultative lithoautotroph Nitrobacter hamburgensis.
abstract: Nitrobacter hamburgensis X14 is a facultative lithoautotroph that conserves energy from the oxidation of nitrite (NO(-)2) and fixes carbon dioxide (CO(2)) 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 NO(-)2 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 NO(-)2, and served as the sole carbon and energy source for growth in the absence of NO(-)2 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 NO(-)2-grown cells, and the D-lactate-dependent O(2) 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 CO(2) in the presence or absence of NO(-)2, exposure to atmospheric CO(2) or the addition of 0.75 mM sodium carbonate was required for mixotrophic growth and for optimum organotrophic growth on D-lactate.
authors.affiliation: Department of Microbiology, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Shawn R
authors.initials: SR
authors.lastname: Starkenburg
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Arp
authors.affiliation: Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331, USA.|Department of Microbiology, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Bottomley
mesh_terms: D052818:Autotrophic Processes; D002245:Carbon Dioxide / Q000378:metabolism*; D007773:Lactates / Q000737:chemistry / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D009576:Nitrobacter / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D007773:Lactates; D009573:Nitrites; D002245:Carbon Dioxide