Candida potacharoeniae sp. nov. and Candida spenceri sp. nov., two novel galactose-containing ascomycetous anamorphic yeast species isolated in Thailand

Fifteen strains of anamorphic yeasts isolated from various natural substrates collected in various places in Thailand were found to represent two novel species of anamorphic yeast genus Candida based on the sequence analysis of the D1/D2 domain of the large subunit rRNA genes, chemotaxonomic and conventional properties used for the classification of yeasts. These strains are located in the clade including Candida etchellsii and Candida magnoliae. Fourteen strains represented by ST-490(T) (BCC 15176(T)=NBRC 106439(T)= CBS 11674(T)) are closely related to Candida sorbosivorans in the D1/D2 sequences but 11 nucleotides (2.4%) were substituted. The remaining strain, ST-594(T) (=BCC 15278(T)=NBRC 106446(T)=CBS 11673(T)) showed a close relationship to Candida geochares but 21 nucleotides (4.7%) were substituted. Apparently, these strains represent two novel Candida species of the Starmerella clade. The two species are described as Candida potacharoeniae sp. nov. and Candida spenceri sp. nov. in the present paper. Like the most species of this clade, the two species contain galactose in the cells in addition to glucose and mannose and have high mol% G + C of 54.4-55.9 and 54.9, respectively.     

Two new anamorphic yeasts, Candida thailandica sp. nov. and Candida lignicola sp. nov., isolated from insect frass in Thailand

Two new yeast strains of the genus Candida were isolated from insect frass collected in Khao-Yai National Park, Nakhonrachasima, Thailand. Based on the morphological, physiological and chemotaxonomic characteristics, and sequence analysis of the D1/D2 domain of 26S rRNA gene, these two strains were found to represent two distinct undescribed species and were named Candida thailandica sp. nov. (ST-17 = BCC 7717(T) = NBRC 102562(T)=CBS 10 610) and Candida lignicola sp. nov. (ST-33 = BCC 7733(T) = NBRC 102564(T) = CBS 10612). In the D1/D2 domain of 26S rRNA gene, C. thailandica (GeneBank accession no. AY228491) differs from Candida tsuchiyae, the nearest species, in 66 nucleotide substitutions (10%) and C. lignicola (GeneBank accession no. AY845350) differs from Candida coipomoensis, the nearest species, in nine nucleotides (1.6%). These two new species are clearly distinguished from their closest species by the assimilation of several carbon compounds.     

Yeasts from phylloplane and their capability to produce indole-3-acetic acid

Yeasts were isolated from the phylloplane of various plant species collected from seven provinces in Thailand. A total of 114 yeast strains and 10 strains of a yeast-like fungus were obtained by enrichment isolation from 91 out of 97 leaf samples (93.8?%). On the basis of the D1/D2 domain of the large subunit rRNA gene sequence similarity, 98 strains were identified to be of 36 yeast species in 18 genera belonging to Ascomycota viz. Candida, Clavispora, Cyberlindnera, Debaryomyces, Hanseniaspora, Hyphopichia, Kazachstania, Kluyveromyces, Kodamaea, Lachancea, Metschnikowia, Meyrozyma, Pichia, Starmerella, Torulaspora and Wickerhamomyces, and to Basidiomycota viz. Sporidiobolus and Trichosporon. Three strains were found to represent two novels Candida species which were previously described as C. sirachaensis and C. sakaeoensis. Ten strains of yeast-like fungus were identified as Aureobasidium pullulans of the phylum Ascomycota. Ascomycetous yeast species accounted altogether for 98.0?% of the 98 strains. The prevalent species was Candida tropicalis with a low frequency of isolation (14.3?%). Diversity of yeasts other than ballistoconidium-forming yeast in phylloplane in a tropical country in Asia has been reported for the first time. All strains obtained were accessed for the capability to produce IAA and result revealed that 39 strains in 20 species, one strain each of an undescribed and a novel species, and two unidentified strains showed the capability of producing IAA when cultivated in yeast extract peptone dextrose broth supplemented with 0.1?% l-tryptophan. All five strains of Candida maltosa produced relatively high concentrations of IAA.     

Candida nonsorbophila sp. nov., a new ascomycetous yeast species isolated in Thailand

Four yeast strains, RS42, SSK10, ST-520 and ST-521, isolated from water in a mangrove forest, bark of a tree and fruit of Ficus sp., respectively, were found to represent a hitherto undescribed anamorphic species. The four strains are related to Candida sinolaborantium in the D1/D2 domain of the large subunit rRNA gene, but differed by eight nucleotide substitutions and two indels, and for this reason are regarded as members of a separate species. Because ascospore formation was not detected, it is described as a new species of Candida, Candida nonsorbophila sp. nov. The type strain is RS42^T (BCC 25963^T=NBRC 103860^T=CBS 10862^T). This species is distinguished from C. sinolaborantium by the inability to assimilate l -sorbose, l -rhamnose and galactitol, and a higher maximum growth temperature.     

The diversity of culturable yeasts in the phylloplane of rice in Thailand

One hundred and fifty-six yeast strains were obtained by the enrichment technique from the phylloplanes of 85 rice leaf samples collected from seven provinces in Thailand. On the basis of the D1/D2 domain of the large subunit rRNA gene sequence analysis, 156 strains were identified as 34 known species in 18 genera consisting of 25 species in 13 genera of the phylum Ascomycota and nine species in five genera of the phylum Basidiomycota. The species in the phylum Ascomycota comprised 24 species in 12 genera of the order Saccharomycetales and one species viz. Yarrowia lipolytica in Saccharomycetales incertae sedis. The 24 species viz. Candida glabrata in the Nakaseomyces clade of Saccharomycetaceae, Candida jaroonii, Candida membranifaciens and Candida terebra in the Yamadazyma clade of Debaryomycetaceae, Candida pseudolambica in the Pichia clade of Pichiaceae, Candida ruelliae in the Metschnikowia clade of Metschnikowiaceae, and three unaffiliated clade Candida species (Candida catenulata, Candida rugosa and Candida tropicalis); Clavispora lusitaniae, Kodamaea ohmeri, Metschnikowia koreensis and Metschnikowia lopburiensis in Metschnikowiaceae; Cyberlindnera fabianii, Cyberlindnera rhodanensis and Wickerhamomyces ciferrii in Wickerhamomycetaceae; Debaryomyces nepalensis, Meyerozyma caribbica, Meyerozyma guilliermondii, Millerozyma koratensis, and Yamadazyma mexicanum in Debaryomycetaceae; Pichia kudriavzevii in Pichiaceae; and Lachancea thermotolerans in Saccharomycetaceae. The species in Basidiomycota viz. Cryptococcus flavescens, Cryptococcus laurentii, Cryptococcus aff. laurentii and Cryptococcus rajasthanensis in the Tremellales lineage, Bulleromyces clade, Tremellales, Tremellomycetes, Agaricomycotina; Pseudozyma antarctica and Pseudozyma aphidis in Ustilaginales, Ustilaginomycetes, Ustilaginomycotina; Rhodotorula taiwanensis and Sporobolomyces blumeae in Sporidiobolales, Microbotryomycetes, Pucciniomycotina; and Trichosporon asahii in Trichosporonales, Tremellomycetes, Agaricomycotina. The most prevalent species was R. taiwanensis with a 23 % frequency of occurrence followed by Candida tropicalis (16 %) and Cryptococcus fabianii (12 %).     

Pseudozyma vetiver sp. nov., a novel anamorphic ustilaginomycetous yeast species isolated from the phylloplane in Thailand

Three strains representing one novel yeast species were isolated from the phylloplanes of the vetiver grasses (DMKU-LV90 and DMKU-LV99^T) and sugarcane (DMKU-SP260) collected in Thailand by leaf washing followed by a plating technique. On the basis of morphological, biochemical, physiological and chemotaxonomic characteristics and the sequence analysis of the D1/D2 region of the large subunit (LSU) rRNA gene and the internal transcribed spacer region (ITS), the three strains were found to represent a single novel anamorphic ustilaginomycetous yeast species in the genus Pseudozyma. The name Pseudozyma vetiver sp. nov. is proposed for this novel species. The type strain is DMKU-LV99^T (BCC 61021 = CBS 12824). The novel species showed phylogenetic relationships to the other members of the genus Pseudozyma and to teleomorphic fungal genera, namely Ustilago, Sporisorium and Anomalomyces in Ustilaginaceae, Ustilaginales. The three strains showed identical sequences both in the D1/D2 and ITS regions. The Pseudozyma species closest to the novel species in terms of pairwise sequence similarity in the D1/D2 region was Pseudozyma pruni but with 2.3 % nucleotide substitutions (14 nucleotide substitutions and no gaps out of 606 nt). The novel species and P. pruni differed by 10.9 % nucleotide substitutions (75 nucleotide substitutions and 31 gaps out of 691 nt) in the ITS region. The phylogenetic analysis based on the combined sequences of the ITS region and the D1/D2 region of the LSU rRNA gene showed that the novel species was found to be most closely related to Pseudozyma fusiformata but with 2.9 % nucleotide substitutions in the D1/D2 region and 7.4 % nucleotide substitutions in the ITS region.     

Endophytic yeast diversity in leaf tissue of rice,corn and sugarcane cultivated in Thailand assessed by a culture-dependent approach

Endophytic yeasts are yeast that can colonize healthy plant tissues without causing any damage to the host plant. This work aimed to explore the diversity of endophytic yeasts in leaf tissue of main agricultural crops (rice, corn and sugarcane) in Thailand, by a culture-dependent approach. A total of 311 leaf samples, consisting of rice (n = 100), corn (n = 109) and sugarcane (n = 102). From the tissue of rice (n = 92), corn (n = 76) and sugarcane (n = 78) leaf samples, 117, 118 and 123 yeast strains were respectively isolated and identified based on the D1/D2 region of the large subunit (LSU) rRNA gene sequence analysis to be yeast species in both the phyla Basidiomycota and Ascomycota. Higher numbers of basidiomycetous yeast than ascomycetous yeast were detected in the leaf tissue of the three crops. Pseudozyma (Dirkmeia) churashimaensis (Ustilaginales) was the most prevalent yeast species in the rice and corn leaves with relative frequencies (RF) of 35.9 % and 17.8 %, respectively. Whereas the predominant species in the sugarcane leaves was Meyerozyma caribbica (Saccharomycetales) with an RF of 14.6 %. In addition, six new yeast species and one new yeast genus were proposed. Our findings suggest that these plant species are good sources from which new yeast species may be isolated.     

Effects of temperature and relative humidity on Aflatoxin B1 reduction in corn grains and antagonistic activities against Aflatoxin-producing Aspergillus flavus by a volatile organic compound-producing yeast,Kwoniella heveanensis DMKU-CE82

As shown in our previous study, Kwoniella heveanensis DMKU-CE82, a volatile organic compound (VOC)-producing yeast, demonstrated promising antagonistic activity against aflatoxin-producing strain of Aspergillus flavus. This yeast’s volatile organic compounds (VOCs) could reduce Aflatoxin B1 (AFB1) in corn grains. In the current study, we evaluated the effect of temperatures and relative humidity on AFB1 reduction during grain storage when co-incubated with this VOC-producing yeast. The VOCs produced by K. heveanensis DMKU-CE82 could promote reduction of AFB1 to less than 20 part per billion (ppb) in the fungal contaminated corn grains under most storage conditions at 35 °C. The major VOCs produced by 2-, 4-, and 6-day-old yeast cultures were closely matched to 3-methyl-1-butanol, 2-methyl-1-butanol, hydrazine-1-1-dimethyl, and butanoic acid-3-methyl. In addition, this yeast strain had the ability to produce β-1,3-glucanase, amylase, cellulase, chitinase, siderophores, and biofilms. Scanning electron microscopy also confirmed the antagonistic activity of K. heveanensis DMKU-CE82 as it caused structural damage to conidia and inhibited the development of mycelia and conidiophores in both direct fungal–yeast interaction and the VOC method in corn grains. These results demonstrated that this yeast strain could be a promising biocontrol agent against aflatoxin-producing fungi in agricultural products.