SILICIBACTER-LACUSCAERULENSIS GEN. NOV., SP. NOV., A MESOPHILIC MODERATELY HALOPHILIC BACTERIUM CHARACTERISTIC OF THE BLUE LAGOON GEOTHERMAL LAKE IN ICELAND

Mesophilic, moderately halophilic bacteria were isolated from a silica -rich geothermal lake, the Blue Lagoon in Iceland. The isolates are st rictly aerobic, but reduce nitrate to nitrite, and are oxidase-and cat alase-positive. The nonsporeforming and nonmotile Gram negative rods a re 0.6-0.8 I-lm in diameter and variable in length (9-18 mu m). and co ntain gas vacuoles. The GC content in their DNA is 66.15%. The minimum , optimum. and maximum temperatures for growth are 22 degrees C, 45 de grees C, and 50 degrees C, respectively. The isolates do not grow with out added salt in the medium and can grow at up to 7% NaCl (w/v). The optimal salinity for growth is 3.5%-4% NaCl. The pH range for growth i s 6.5-8.5, with the optimal pH at 7.0. At optimal conditions the bacte rium has a doubling time of 80 min. The main cytochrome is a membrane- bound cytochrome c with an alpha-peak at 549 nm. Sequencing of 165 rRN A from the type strain ITI-1157 revealed it to be a proteobacterium of the alpha-subclass with the closest relatives being Roseobacter litor alis and Paracoccus kocurii. The new isolates do not contain bacterioc hlorophyll a and are considered to represent a new genus and a new spe cies. Silicibacter lacuscaerulensis.