Molecular Ecology And Functions Of Yeasts In Different Wasterwater Treatment Systems

The yeast distribution and diversity properties in three different wastewater treatment systems (WWTSs), including fermentation (FWWTS), municipal (MWWTS), and papermaking (PWWTS) wastewater treatment systems, were investigated by PCR-DGGE and cultivation-dependent methods. Moreover, the related enzyme activities of isolated strains were detected in order to study the ecological functions of yeasts in WWTSs. The conclusions were drawn as follows:(1) The DGGE profiles showed that yeast community assemblages in activated sludge samples were much diverse. The results of cluster analysis revealed that the yeast species distribution was closely related to the characteristics of different wastewater. The sequencing analysis results of selected bands indicated that dominant yeast species were different in three studied WWTSs. The FWWTS showed the highest dominant yeasts diversity with a possible novel species and 12 species in 9 genera (Candida sorbophila, Candida tropicalis, Dipodascus capitatus, Filobasidium uniguttulatum, Kluyveromyces marxianus, Issatchenkia occidentalis / Pichia kudriavzevii, Saccharomyces cerevisiae and Debaryomyces sp., Geotrichum sp. / Galactomyces sp., Pichia sp., Trichosporon sp.). The excellent species in MWWTS were Candida sorbophila, Filobasidium uniguttulatum, Kluyveromyces marxianus, Saccharomyces cerevisiae, one Debaryomyces sp., two Trichosporon sp. and an unknown classification unit. The species Candida tropicalis and Debaryomyces sp. were the predominant yeasts in PWWTS. Furthermore, the differences in yeast biodiversity between the different treatment units were also observed.(2) Total 153 yeast isolates were recovered from the three WWTSs and identified using molecular methods. The isolations were identified as 42 species in17 genera and distributed in 39 different ITS-RFLP groups. In the MWWTS, Candida parapsilosis was the dominant species-specific and the following excellent species were Candida tropicalis, Dipodascus ovetensis, Rhodotorula mucilaginosa and Trichosporon montevideense. Meanwhile, Rhodotorula mucilaginosa was the major species in the FWWTS. With regard to PWWTS, the most abundant species were Pichia guilliermondii, followed by Stephanoascus ciferrii and Candida allociferrii, and these species were not obtained from the other WWTSs. Most of the minor yeast populations were characteristic for the particular WWTS or even treatment unit-specific. In addition, yeast populations could be simultaneously found in any two WWTSs among studied systems.(3) The analysis results of PCR-DGGE and cultivation-dependent methods have been compared and showed that ascomycetous yeasts were prevalent groups, in which the genus Candida was most dominant and Candida tropicalis was excellent species. The basidiomycetous yeast group of Trichosporon was sub-dominant. The sequence order of yeast diversity was FWWTS>MWWTS>PWWTS. Only one species of genus Debaryomyces broadly distributed in all studied WWTSs. Furthermore, six species of Candida sorbophila, Candida tropicalis, Filobasidium uniguttulatum, Issatchenkia orientalis / Pichia kudriavzevii, Saccharomyces cerevisiae, and Trichosporon montevideense could be detected ether using PCR-DGGE or using traditional method. The species Kluyveromyces marxianus have been detected through PCR-DGGE but not cultivation-dependent method, while various species of Cryptococcus sp. and Rhodotorula sp. were not detected by PCR-DGGE.(4) The analysis results of extracellular hydrolytic enzymes showed that all isolated yeast strains were not detected amylase activity. The species Candida parapsilosis, Dipodascus ovetensis, Filobasidium uniguttulatum and Geotrichum klebahnii have been detected lipase activity. The protease activity was detected by the species Cryptococcus albidus, Pichia membranifaciens, Pichia spartinae and Rhodotorula mucilaginosa. Four species Candida palmioleophila, Candida tropicalis, Trichosporon montevideense and Yarrowia lipolytica could produce lipase and protease. In the presence of Reactive Red M-3BE, the ligninolytic enzymes were detected. The results proved that 43 strains identified as 17 different yeast species in 8 genera were detected manganese dependant peroxidase (MnP) activity and many strains were the genera Candida, Pichia and Rhodotorula. The species Candida boidinii, Candida ghanaensis, Candida parapsilosis and Candida zeylanoides were detected lignin peroxidase (LiP) activity. The laccase (Lac) activity were not detected by all isolations.(5) Decolorization of Reactive Red M-3BE by isolated strains was analyzed and the results showed that 139 isolations could decolorize the dye within 12~72 h. Moreover, extensive color removal of the dye could be obtained by 10 strains within 12 h and the decolorization (%) exceeded 90%. Other 38 strains could decolorize the dye in 24 h with the color removal efficiency of 81.28~99.82%.