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

Abstract

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 (E_H) 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.

Keywords: diversity; duckweed; plant growth promotion; yeast.

Figure 1.. Percentage of yeast genera found in duckweed samples, a) yeast in the phylum Ascomycota, b) yeast in the phylum Basidiomycota.

Figure 2.. Phylogenetic placement of known species of the representative yeast species from duckweed (phylum Ascomycota) based on sequences of the D1/D2 region of the LSU rRNA gene. Reference sequences retrieved from the GenBank database are included. The tree was constructed with the maximum-likelihood method and the GTR evolutionary model. Numbers on the branches represent the bootstrap values (>50%) from 1000 random replicates. The scale bar corresponds to a genetic distance of 0.1 substitutions per position. Schizosaccharomyces pombe NRRL Y-12796^T (JQ689077) was used as an outgroup in this analysis. a) A part of the tree showing the phylogenetic relationships of a partial taxa within Debaryomycetaceae, Saccharomycetales incertae sedis, Trichomonascaceae, Phaffomycetaceae, Pichiaceae, Saccharomycodaceae and Saccharomycetaceae b) Part of the tree that shows the phylogenetic relationships of another partial taxa within Metschnikowiaceae, Saccharomycetales incertae sedis and Pichiaceae.

Figure 3.. Phylogenetic placement of known species of the representative yeast species from duckweed (phylum Basidiomycota) based on the sequence of the D1/D2 region of the LSU rRNA gene. Reference sequences retrieved from the GenBank database are included. The tree was constructed with the maximum-likelihood method and the GTR evolutionary model. Numbers on the branches represent the bootstrap values (>50%) from 1000 random replicates. The scale bar corresponds to a genetic distance of 0.05 substitutions per position. Schizosaccharomyces pombe NRRL Y-12796^T (JQ689077) was used as an outgroup in this analysis.

Figure 4.. Principal Coordinate Analysis (PCoA) plots of yeast communities on duckweed samples using Jaccard similarity coefficient.

Figure 5.. Species accumulation curves showing the relationship between the number of duckweed samples and the number of observed species. Chao 1, Jack 1 and bootstrap species richness estimators were plotted.