Kluyveromyces siamensis sp. nov., an ascomycetous yeast isolated from water in a mangrove forest in Ranong Province, Thailand.

Seven strains of a novel Kluyveromyces species were isolated from seven water samples collected from a mangrove forest. Analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene sequences revealed that the sequences of five strains (RS8(T), RS20, RS54, RV42 and RV89) were identical and differed from the other two strains (RS65 and RV153) by only one nucleotide substitution in 544 nucleotides (nt). The closest species in terms of pairwise sequences similarity was Kluyveromyces aestuarii, but the level of nucleotide substitution (six to seven nucleotide substitutions in 544 nt) was sufficient to justify the description of a separate species. The phylogenetic tree based on the sequence of the D1/D2 domain of the LSU rRNA gene rather suggested that the new species is a sister species of K. aestuarii and forms a clade with the other six recognized species of Kluyveromyces. Sequence analysis of the internal transcribed spacer (ITS1-5.8S rRNA gene-ITS2) region supported their distinct status as a species. The phenotypic characteristics of the seven strains were typical of the genus Kluyveromyces. On this basis, the seven strains were assigned to a single novel species of the genus Kluyveromyces, for which the name Kluyveromyces siamensis sp. nov. is proposed. The type strain is RS8(T) (BCC 25962(T)=NBRC 103859(T)=CBS 10860(T)).