Gracilibacter thermotolerans gen. nov., sp nov., an anaerobic, thermotolerant bacterium from a constructed wetland receiving acid sulfate water

An obligatorily anaerobic, thermotolerant, asporogenic bacterium, strain JW/YJL-S1(T) was isolated from a sediment sample of a constructed wetland system receiving acid sulfate water (pH 1-6-3-0). Cells of strain JW/YJL-S1(T) were straight to curved rods 0-2-0-4 mu m in diameter and 2-0-7-0 mu m in length, and stained Gram-negative. Growth of strain JW/YJL-S1T was observed at 25-54 degrees C (no growth at or below 20 or at or above 58 degrees C), with an optimum temperature range for growth of 42-5-46-5 degrees C. The pH(25 degrees C) range for growth was 6-0-8-25 (no growth at or below pH 5-7 or at or above pH 8-5), with optimum growth at pH 6-8-7-75. The salinity range for growth was 0-1-5% (w/v) NaCl, with an optimum at 0-0-5 %, During growth on glucose the isolate produced acetate, lactate and ethanol as main fermentation end products. The fatty acid composition was dominated by branched-chain compounds: i15: 0, a15: 0, i16: 0 and i17: 0. The G+C content of the genomic DNA was 42-8 mol% (HPLC). Strain JW/YJL-S1(T) showed polymorphism of the 16S rRNA gene. Its closest relative was the thermophilic Clostridium thermosuccinogenes DSM 5807 T (a member of Clostridium cluster III) (a BLASTN search revealed Clostridium pascui DSM 10365 T to have 92-7 % gene sequence similarity, the highest value). The inferred phylogenetic trees placed strain JW/YJL-S1(T) between Clostridium clusters I/II and III. Based on the morphological and phylogenetic data presented, JW/YJL-S1(T) (= DSM 17427(T) = ATCC BAA-1219(T)) is proposed as the type strain of a novel species in a new genus, Gracilibacter thermotolerans gen. nov., sp. nov.