Heliorestis daurensis, gen. nov sp nov., an alkaliphilic rod-to-coiled-shaped phototrophic heliobacterium from a Siberian soda lake

A novel alkaliphilic heliobacterium was isolated from microbial mars of a l ow-salt alkaline Siberian soda lake. Cells of the new organism were tightly coiled when grown in coculture with a rod-shaped bacterium, but grew as sh ort filaments when finally obtained in pure culture. The new phototroph, de signated strain BT-H1, produced bacteriochlorophyll g and a neurosporene-li ke pigment, and lacked internal photosynthetic membranes. Similar to other heliobacteria, strain BT-H1 grew photoheterotrophically on a limited range of organic compounds including acetate and pyruvate. Sulfide was oxidized t o elemental sulfur and polysulfides under photoheterotrophic conditions; ho wever, photoautotrophic growth was not observed. Cultures of strain BT-H1 w ere alkaliphilic, growing optimally at pH 9, and unlike other heliobacteria , they grew optimally at a temperature of 25 degrees C rather than at 40 de grees C or above. Analysis of the 16S rRNA gene sequence of the new organis m showed that it groups within the heliobacterial clade. However, its branc hing order was phylogenetically basal to all previously investigated specie s of heliobacteria. The G+C content of the DNA of strain BT-H1 (44.9 mol%) was also quite distinct from that of other heliobacteria. This unique assem blage of properties implicates strain BT-H1 as a new genus and species of t he heliobacteria, Heliorestis daurensis, named for its unusual morphology ( "restis" is Latin for "rope") and for the Daur Steppe in Russia in which th ese soda lakes are located.