Diversity of duckweed (Lemnaceae) associated yeasts and their plant growth promoting characteristics.

The diversity of duckweed (Lemnaceae) associated yeasts was studied using a culture-dependent method. A total of 252 yeast strains were isolated from 53 duckweed samples out of the 72 samples collected from 16 provinces in Thailand. Yeast identification was conducted based on the D1/D2 region of the large subunit (LSU) rRNA gene sequence analysis. It revealed that 55.2% and 44.8% yeast species were Ascomycota and Basidiomycota duckweed associated yeasts, respectively. Among all, Papiliotrema laurentii, a basidiomycetous yeast, was found as the most prevalent species showing a relative of frequency and frequency of occurrence of 21.8% and 25%, respectively. In this study, high diversity index values were shown, indicated by the Shannon-Wiener index (H'), Shannon equitability index (EH) and Simpson diversity index (1-D) values of 3.48, 0.86 and 0.96, respectively. The present results revealed that the yeast community on duckweed had increased species diversity, with evenness among species. Principal coordinate analysis (PCoA) revealed no marked differences in yeast communities among duckweed genera. The species accumulation curve showed that the observed species richness was lower than expected. Investigation of the plant growth promoting traits of the isolated yeast on duckweed revealed that 178 yeast strains produced indole-3-acetic acid (IAA) at levels ranging from 0.08-688.93 mg/L. Moreover, siderophore production and phosphate solubilization were also studied. One hundred and seventy-three yeast strains produced siderophores and exhibited siderophores that showed 0.94-2.55 activity units (AU). One hundred six yeast strains showed phosphate solubilization activity, expressed as solubilization efficiency (SE) units, in the range of 0.32-2.13 SE. This work indicates that duckweed associated yeast is a potential microbial resource that can be used for plant growth promotion.

Magnusiomyces siamensis sp. nov., a yeast-like fungus isolated from food waste.

Three yeast strains, DMKU-GTSP8-6, DMKU-GTSP8-14T and DMKU-JED8-73, were isolated from food waste in Thailand. Based on the phenotypic characteristics and sequence analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) region, it was revealed that the three strains clustered with the Magnusiomyces/Saprochaete clade. These strains were distinguished from the closely related species Saprochaete quercus CBS 750.85, Magnusiomyces ovetensis CBS 192.55T, Magnusiomyces starmeri CBS 780.96T, Saprochaete chiloensis CBS 8187T and Magnusiomyces ingens CBS 517.90T by 11.4, 13.1, 11.9, 11.2 and 12.6 % sequence divergence in the D1/D2 domain and by 34.6, 34.5, 33.6, 33.2 and 34.9 % sequence divergence in the ITS region, respectively. The new species, which does not produce ascospores, is described as Magnusiomyces siamensis. The holotype of Magnusiomyces siamensis is TBRC 15056T, and the isotypes are DMKU-GTSP8-14T and PYCC 9023T.

Pichia bovicola sp. nov., a yeast species associated with small-intestinal content of cattle.

Three yeast strains, DMKU-MP6-4T, DMKU-MP2-6 and DMKU-MP5-1, were isolated from the small-intestinal content or Pia of cattle in Thailand during the investigation of yeast diversity in this habitat. According to the D1/D2 domain of the large subunit (LSU) rRNA gene and internal transcribed spacer (ITS) region sequence analysis, these strains represent a novel yeast species in the genus Pichia. The species produced one to four ascospores per ascus with spherical to ellipsoidal shape and heterogenous in terms of size. These three strains were identical and differed from their closely related species, Pichia exigua NRRL Y-10920T by 2% (six nucleotide substitutions and five gaps) in the D1/D2 domain of the large subunit rRNA gene, while ITS region sequences differed by 3.1% (16 nucleotide substitutions and 27 gaps), 3.7% (19 nucleotide substitutions and 28 gaps) and 3.1% (16 nucleotide substitutions and 27 gaps) for DMKU-MP6-4T, DMKU-MP2-6 and DMKU-MP5-1, respectively. The name, Pichia bovicola, is proposed to accommodate these species. The holotype is DMKU-MP6-4T (TBRC 15616T=PYCC 8905T).

Wickerhamiella martinezcruziae f. a., sp. nov., a yeast species isolated from tropical habitats.

Four yeast isolates with an affinity to the genus Wickerhamiella were obtained from beach sand, a marine zoanthid and a tree exudate at different localities in Brazil. Two other isolates with almost identical ITS and D1/D2 sequences of the large subunit rRNA gene were isolated from the small intestine of cattle and a grease trap in Thailand. These isolates represent a novel species phylogenetically related to Wickerhamiella verensis, Wickerhamiella osmotolerans, Wickerhamiella tropicalis, Wickerhamiella sorbophila and Wickerhamiella infanticola. The novel species differs by 15-30 nucleotide differences from these species in the D1/D2 sequences. The name Wickerhamiella martinezcruziae f.a., sp. nov. is proposed. The holotype of Wickerhamiella martinezcruziae sp. nov. is CBS 16104T. The MycoBank number is MB 839328.

Yeasts Associated with the Small-Intestinal Contents and Epithelium of Pon Yang Kham (Charolais Crossbred) Fattening Beef Cattle.

Yeast diversity in the pia and small-intestinal epithelium of Pon Yang Kham fattening cattle in Thailand was studied using a culture-dependent method. A total of 701 yeasts were isolated from the pia of the duodenum, jejunum, and ileum of the small intestine, while 425 isolates were obtained from the epithelium of all three parts of the small intestine. Yeast identification was performed and ascomycetous yeasts were found at levels of 96.9% and 86.8% in the pia and small intestine, respectively, whereas basidiomycetous yeasts were found at levels of 2.3% and 12.7%. Candida parapsilosis was the species with the highest occurrence in the duodenal and jejunal pia, with an 83.3% and 77.8% frequency of occurrence (FO), respectively. Both C. parapsilosis and C. tropicalis were species with the highest occurrence in the ileum, with a 61.1% FO. Moreover, C. parapsilosis was the species with the highest occurrence in the epithelium of the duodenum, jejunum, and ileum, with FOs of 88.2%, 87.5%, and 87.2%, respectively. Principal coordinate analysis revealed no marked differences in yeast communities from either the pia or epithelium of all three parts of the small intestine. An estimation of the expected richness of the species showed that the observed species richness was lower than the predicted richness.

Savitreea pentosicarens gen. nov., sp. nov., a yeast species in the family Saccharomycetaceae isolated from a grease trap.

Two strains (DMKU-GTCP10-8 and CLIB 1740) representing a novel anamorphic yeast species were isolated from a grease sample collected from a grease trap in Thailand and from an unidentified fungus collected in French Guiana, respectively. On the basis of phylogenetic analysis based on the combined D1/D2 domain of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) region, Lachancea fermentati CBS 707T was the closely related species with 12.8 % sequence divergence (70 nucleotide substitutions and three gaps in 571 nucleotides) and 28.1 % sequence divergence (93 nucleotide substitutions and 90 gaps in 651 nucleotides) in the D1/D2 domain of the LSU rRNA gene and the ITS region, respectively. Phylogenetic analysis based on the concatenated sequences of the five genes including the small subunit rRNA gene, the D1/D2 domain of the LSU rRNA gene, the ITS region, translation elongation factor-1 alpha (TEF1) and RNA polymerase II subunit 2 (RPB2) genes confirmed that the two strains (DMKU-GTCP10-8 and CLIB 1740) were well-separated from other described yeast genera in Saccharomycetaceae. Hence, Savitreea pentosicarens gen. nov., sp. nov. is proposed to accommodate these two strains as members of the family Saccharomycetaceae. The holotype is S. pentosicarens DMKU-GTCP10-8T (ex-type strain TBRC 12159=PYCC 8490; MycoBank number 835044).

Limtongozyma siamensis gen. nov., sp. nov., a yeast species in the Saccharomycetales and reassignment of Candida cylindracea to the genus Limtongozyma.

Two yeast strains, DMKU-WBL1-3 and DMKU GT3-16, were obtained from grease samples collected from grease traps at the Kasetsart University canteen, Thailand. Pairwise sequence analysis indicated that the strains were closely related to Candida cylindracea NRRL Y-17506T, but differed by 11 and 35 nucleotide substitutions in the D1/D2 domain of the large subunit (LSU) rRNA gene and the ITS region, respectively. Based on sequence divergences, the novel species was distinguished from C. cylindracea. The results of phylogenetic analysis based on the concatenated sequences from small subunit rRNA, ITS region and LSU rRNA genes showed that the two strains and C. cylindracea NRRL Y-17506T formed a distinct lineage related to the genus Babjeviella. A novel genus, Limtongozyma, is proposed to accommodate these clade members. Hence, Candida cylindracea NRRL Y-17506T is transferred to this genus and assigned as the type species of the genus. The holotype of Limtongozyma siamensis is DMKU-WBL1-3.

Grease Waste as a Reservoir of Lipase-Producing Yeast and Description of Limtongella siamensis gen. nov., sp. nov.

A total of 175 yeast isolates were obtained from grease samples. Based on the D1/D2 region of the large subunit (LSU) ribosomal RNA (rRNA) gene analysis, 150 yeast isolates were identified as belonging to 36 described yeast species, whereas 25 isolates required more analysis. Among the described species, Rhodotorula mucilaginosa was the only Basidiomycetous yeast, whereas 149 isolates were identified as belonging to 35 described species of 15 genera in the phylum Ascomycota, and Candida tropicalis was the most abundant species. A study of lipase production indicated that strain DMKU-JMGT1-45 showed volumetric activity of 38.89 ± 9.62 and 155.56 ± 14.70 U/mL when grown in yeast extract malt extract (YM) and YM supplemented with 1% olive oil, respectively. In addition, this strain intracellularly accumulated lipid, of which the fatty acid profile revealed the major fatty acids to be 39.9% oleic acid (C18:1), 27.61% palmitoleic acid (C16:1) and 14.97% palmitic acid (C16:0). A phylogenetic analysis of the combined multi-locus gene sequences showed that the strains DMKU-JMGT1-45T and DMKU-JMGT4-14 formed a well-separated lineage and could not be assigned to any of the currently recognized genera of the Saccharomycetales. Limtongella siamensis gen. nov., sp. nov. is therefore proposed to accommodate these two strains as members of the order Saccharomycetales.