Halomonas mongoliensis sp. nov. and Halomonas kenyensis sp. nov., new haloalkaliphilic denitrifiers capable of N2O reduction, isolated from soda lakes

Abstract

In the course of the search for N2O-utilizing microorganisms, two novel strains of haloalkaliphilic denitrifying bacteria, Z-7009 and AIR-2, were isolated from soda lakes of Mongolia and Kenya. These microorganisms are true alkaliphiles and grow in the pH ranges of 8.0-10.5 and 7.5-10.6, respectively. They are facultative anaerobes with an oxidative type of metabolism, able to utilize a wide range of organic substrates and reduce nitrate, nitrous oxide, and, to a lesser extent, nitrite to gaseous nitrogen. They can oxidize sulfide in the presence of acetate as the carbon source and nitrous oxide (strain Z-7009) or nitrate (strain AIR-2) as the electron acceptor. The strains require Na+ ions. They grow at medium mineralization levels of 0.16-2.2 M Na+ (Z-7009) and 0.04-2.2 M Na+ (AIR-2). The G+C contents of the DNA of strains Z-7009 and AIR-2 are 67.9 and 65.5 mol %, respectively. According to the results of 16S rRNA gene sequencing and DNA-DNA hybridization, as well as on the basis of physiological properties, the strains were classified as new species of the genus Halomonas: Halomonas mongoliensis, with the type strain Z-7009T (=DSM 17332, =VKM B2353), and Halomonas kenyensis, with the type strain AIR-2T (=DSM 17331, =VKM B2354).