Pichia thermomethanolica sp. nov., a novel thermotolerant, methylotrophic yeast isolated in Thailand.

Three strains (N002, N069 and PT31(T)) of a novel thermotolerant methylotrophic yeast species belonging to the genus Pichia were isolated from soil collected in Thailand by three consecutive enrichments in methanol broth at room temperature. They were categorized as thermotolerant strains on the basis of their good growth below 20 degrees C and up to a high temperature (37 degrees C). The major characteristics of the three strains included the following and placed them in the genus Pichia: the formation of four helmet-/hat-shaped ascospores in a deliquescent ascus that might be unconjugated or produced by conjugation between a cell and its bud or between independent cells; multilateral budding; the presence of ubiquinone Q-7; negative for Diazonium blue B colour and urease reactions; and the absence of arthrospores and ballistospores. The three strains differed by one to three nucleotide substitutions in the sequences of the D1/D2 domain of the large-subunit rDNA sequence. Phylogenetic analysis revealed that their closest species was Pichia dorogensis, but with 11-13 nucleotide substitutions in 554 nt. The phenotypic characteristics of the three strains were the same. The strains could be distinguished from P. dorogensis by a number of phenotypic characteristics. On the basis of the above findings, these three strains were assigned to a single novel species of Pichia, for which the name Pichia thermomethanolica sp. nov. is proposed. The type strain is PT31(T) (=BCC 16875(T)=JCM 12984(T)=CBS 10098(T)).