Identification and Characterization of a Freshwater Pyrococcus sp. Strain PK 5017 and Identification of Pfu-Like IS Elements in Thermococcus sibiricus MM 739

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 ?m. Temperature, pH and NaCl concentration ranges for growth are 75-105 oC (opt. temp. = 95-100 oC), 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 So containing media. Growths on maltose, trehalose, starch and xylitol occur in So-free media. No growth occurs on dextrose, sucrose, xylose, sorbitol, mannose and cellobiose. So 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.