Abstract

Two novel hyperthermophilic, rod-shaped crenarchaeotes were isolated from an acidic hot spring in the Philippines. Cells were mostly straight or slightly curved rods 0.4-0.7 micron in width. Bent cells, branched cells, and cells bearing globular bodies were commonly observed. The isolates were heterotrophs and grew anaerobically and microaerobically. The addition of archaeal cell extract or a vitamin mixture to the medium significantly stimulated growth. The isolates grew over a temperature range of 60-92 degrees C, and optimally around 85 degrees C and grew over a pH range of 2.3-6.4, and optimally at pH 3.7-4.2. The isolates utilized glycogen, gelatin, beef extract, peptone, tryptone and yeast extract as carbon sources. They required sulfur, thiosulfate or sulfate as electron acceptors. The lipids mainly consisted of various cyclized glycerol-bisdiphytanyl-glycerol tetraethers. The G+C content of the genomic DNAs was 43 mol%. The 16S rDNA contained two small introns. The comparison of the 16S rDNA exon sequences revealed that they represented an independent lineage in the family Thermoproteaceae. The two strains were included in a single species because of high levels of DNA-DNA relatedness. From these results, Caldivirga maquilingensis gen. nov., sp. nov. is proposed in the family Thermoproteaceae to accommodate these isolates. The type strain of C. maquilingensis is strain IC-167T (= JCM 10307T = MCC-UPLB 1200T = ANMR 0178T).