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Yeast spores seem to be involved in biological phosphate removal: a microscopic in situ case study
Hannes Melasniemi1,2, Anne Hernesmaa2
1Helsinki University of Technology, Laboratory of Environmental Engineering, PO Box 6100, FIN-02015 HUT, Finland2.
Abstract:
The principal polyphosphate-accumulating organism (PAO) in a biological-phosphate-removal activated-sludge process was assessed microscopically. The organism was recognized by its distinct morphotype most easily after polyphosphate staining. The PAO occurred in large, homogeneous clusters. The cells of the PAO were the biggest cells abounding in the sludge--clearly bigger than average sludge bacteria. Typical of the principal PAO was a variation of cell size, even in fresh sludge. In acetate minimal medium containing ampicillin, the original principal PAO clusters were converted to clusters of clearly larger, polyphosphate-containing, vegetative yeast-like cells. Cycloheximide addition inhibited this and caused flock disintegration, disappearance of the principal PAO clusters and growth of free bacteria. The cell wall of the principal PAO was not of the usual bacterial character. It showed anomalous Gram staining, stained for chitin (not found in bacteria) and bound concanavalin A, like cell walls of many yeasts. In addition, the PAO cell wall was resistant to lysozyme, but sensitive to an enzyme mixture that lyses yeast cell walls. It was concluded that the principal PAO cells in the studied sludge were clustered spores of a yeast.
Insights
The primary organism in biological phosphate removal was identified as yeast spores, not bacteria. Microscopic and chemical analyses confirmed its unique cell wall structure and polyphosphate accumulation capabilities.
Area of Science:
- Microbiology
- Environmental Science
- Biotechnology
Background:
- Biological phosphate removal is crucial for wastewater treatment.
- Identifying the dominant polyphosphate-accumulating organism (PAO) is key to optimizing this process.
- Previous studies have focused on bacterial PAOs, but the principal organism in this study presented unique characteristics.
Purpose of the Study:
- To microscopically and chemically characterize the principal polyphosphate-accumulating organism (PAO) in a biological phosphate removal activated sludge process.
- To determine the taxonomic identity of the dominant PAO.
Main Methods:
- Microscopic observation of activated sludge with polyphosphate staining.
- Culturing the organism in acetate minimal medium with ampicillin.
- Testing cell wall properties using Gram staining, chitin staining, concanavalin A binding, lysozyme sensitivity, and yeast lytic enzyme sensitivity.
Main Results:
- The principal PAO formed large, homogeneous clusters and consisted of large cells, distinct from typical sludge bacteria.
- In specific media, the organism transformed into larger, vegetative yeast-like cells containing polyphosphate.
- Cell wall analysis revealed chitin presence, anomalous Gram staining, concanavalin A binding, and resistance to lysozyme but sensitivity to yeast lytic enzymes.
Conclusions:
- The principal PAO in the studied activated sludge process was identified as clustered spores of a yeast, not a bacterium.
- The unique cell wall composition and polyphosphate accumulation are characteristic of this yeast.
- Understanding this yeast's role can improve biological phosphate removal strategies.