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Alkalilimnicola ehrlichii sp. nov., a novel, arsenite-oxidizing haloalkaliphilic gammaproteobacterium capable of chemoautotrophic or heterotrophic growth with nitrate or oxygen as the electron acceptor

¹ US Geological Survey, 345 Middlefield Road, MS 480, Menlo Park, CA 94025, USA
² Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA
³ Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
⁴ Darling Marine Center, University of Maine, Walpole, ME 04573, USA
⁵ Department of Biology, UCL, London WC1E 6BT, UK

Correspondence
Ronald S. Oremland
roremlan{at}usgs.gov

A facultative chemoautotrophic bacterium, strain MLHE-1^T, was isolated from Mono Lake, an alkaline hypersaline soda lake in California, USA. Cells of strain MLHE-1^T were Gram-negative, short motile rods that grew with inorganic electron donors (arsenite, hydrogen, sulfide or thiosulfate) coupled with the reduction of nitrate to nitrite. No aerobic growth was attained with arsenite or sulfide, but hydrogen sustained both aerobic and anaerobic growth. No growth occurred when nitrite or nitrous oxide was substituted for nitrate. Heterotrophic growth was observed under aerobic and anaerobic (nitrate) conditions. Cells of strain MLHE-1^T could oxidize but not grow on CO, while CH₄ neither supported growth nor was it oxidized. When grown chemoautotrophically, strain MLHE-1^T assimilated inorganic carbon via the Calvin–Benson–Bassham reductive pentose phosphate pathway, with the activity of ribulose 1,5-bisphosphate carboxylase (RuBisCO) functioning optimally at 0.1 M NaCl and at pH 7.3. Strain MLHE-1^T grew over broad ranges of pH (7.3–10.0; optimum, 9.3), salinity (15–190 g l^–1; optimum 30 g l^–1) and temperature (13–40 °C; optimum, 30 °C). Phylogenetic analysis of 16S rRNA gene sequences placed strain MLHE-1^T in the class Gammaproteobacteria (family Ectothiorhodospiraceae) and most closely related to Alkalispirillum mobile (98.5 %) and Alkalilimnicola halodurans (98.6 %), although none of these three haloalkaliphilic micro-organisms were capable of photoautotrophic growth and only strain MLHE-1^T was able to oxidize As(III). On the basis of physiological characteristics and DNA–DNA hybridization data, it is suggested that strain MLHE-1^T represents a novel species within the genus Alkalilimnicola for which the name Alkalilimnicola ehrlichii is proposed. The type strain is MLHE-1^T (=DSM 17681^T=ATCC BAA-1101^T). Aspects of the annotated full genome of Alkalilimnicola ehrlichii are discussed in the light of its physiology.

Further details of the methods used for PCR amplification and gene fragment analysis, graphs showing the growth of strain MLHE-1^T under varying temperature, salinity and pH conditions, an additional phylogenetic tree, a plot showing RuBisCO activity in cell extracts of MLHE-1^T and tables detailing lithotrophic growth of the novel strain on a variety of inorganic electron donors and on a diversity of organic and one-carbon electron donors are available as supplementary material in IJSEM Online.

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