Strain FC2004T, a strictly anaerobic, extremely thermophilic heterotroph, was isolated from a hot spring in Thailand. Typical cells of strain FC2004T were rod shaped (0.5-0.6×1.1-2.5 µm) with an outer membrane swelling out over an end. Filaments (10-30 µm long) and membrane-bound spheroids containing two or more cells inside (3-8 µm in diameter) were observed. The temperature range for growth was 60-88°C (optimum 78-80°C), pH range was 6.5-8.5 (optimum pH 7.5) and NaCl concentration range was 0 to <5 g l-1 (optimum 0.5 g l-1). S0 stimulated growth yield. S2O32- and NO3- did not influence growth. Glucose, maltose, sucrose, fructose, cellobiose, CM-cellulose and starch were utilized for growth. The membrane was composed mainly of the saturated fatty acids C16:0 and C18:0. The DNA G+C content was 45.8 mol%. The 16S rRNA gene sequence of strain FC2004T revealed highest similarity to species of the genus Fervidobacterium: F. pennivorans DSM 9078T (97-96 %), F. islandicum AW-1 (96 %), F. changbaicum CBS-1T (96 %), F. islandicum H21T (95 %), F. nodosum Rt17-B1T (95 %), F. riparium 1445tT (95 %) and F. gondwanense AB39T (93 %). Phylogenetic analysis of 16S rRNA gene sequences and average nucleotide identity analysis suggested that strain FC2004T represented a novel species within the genus Fervidobacterium, for which the name Fervidobacterium thailandense sp. nov. is proposed. The type strain is FC2004T (=JCM 18757T=ATCC BAA-2483T).

A strictly anaerobic, hyperthermophilic Pyrococcus sp. strain PK 5017 (PK 5017) was isolated from a freshwater hot spring in Thailand. Cells of strain PK 5017 are irregular cocci arranging singly and in pairs with a diameter range of 0.7-1.2 μm. Temperature, pH and NaCl concentration ranges for growth are o C (opt. temp. = 95-100 o C), pH 5-7.8 (opt. pH = 7.2) and 2.5-<40 g/l NaCl (opt. conc. = 24 g/l). Growths on the pancreatic digest of casein, yeast extract, peptone, meat extract, beef extract and skim milk (5 g/l ea.) occur in S o containing media. Growths on maltose, trehalose, starch and xylitol occur in S o -free media. No growth occurs on dextrose, sucrose, xylose, sorbitol, mannose and cellobiose. S o is not obligatory for growth, but stimulates growth. G+C content of genome is 42.5 mol%. DNA-DNA hybridization results reveal more similar genome sequence of strain PK 5017 to P. horikoshii than P. furiosus. Genome of strain PK 5017 contains multiple copies of the homologous IS-pfu of elements. Based on the biochemical characteristics and the presence of the homologous IS-pfus, strain PK 5017 is a close relative of P. furiosus. Two copies of IS-pfu homologs named "IS-pfu-Ts1" and "IS-pfu-Ts2" are identified in the complete genome sequence of Thermococcus sibiricus MM 739. Pyrococcus sp. strain PK 5017 = Pyrococcus sp. strain Pikanate 5017 = JCM17043 = ATCC BAA-2246.

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