Anaerobic and aerobic metabolism of glycogen-accumulating organisms selected with propionate as the sole carbon source.

Advanced Wastewater Management Centre, AWMC, The University of Queensland, St Lucia, Brisbane 4072, Australia.
Microbiology (Impact Factor: 2.85). 10/2006; 152(Pt 9):2767-78. DOI: 10.1099/mic.0.28065-0
Source: PubMed

ABSTRACT In the microbial competition observed in enhanced biological phosphorus removal (EBPR) systems, an undesirable group of micro-organisms known as glycogen-accumulating organisms (GAOs) compete for carbon in the anaerobic period with the desired polyphosphate-accumulating organisms (PAOs). Some studies have suggested that a propionate carbon source provides PAOs with a competitive advantage over GAOs in EBPR systems; however, the metabolism of GAOs with this carbon source has not been previously investigated. In this study, GAOs were enriched in a laboratory-scale bioreactor with propionate as the sole carbon source, in an effort to better understand their biochemical processes. Based on comprehensive solid-, liquid- and gas-phase chemical analytical data from the bioreactor, a metabolic model was proposed for the metabolism of propionate by GAOs. The model adequately described the anaerobic stoichiometry observed through chemical analysis, and can be a valuable tool for further investigation of the competition between PAOs and GAOs, and for the optimization of the EBPR process. A group of Alphaproteobacteria dominated the biomass (96 % of Bacteria) from this bioreactor, while post-fluorescence in situ hybridization (FISH) chemical staining confirmed that these Alphaproteobacteria produced poly-beta-hydroxyalkanoates (PHAs) anaerobically and utilized them aerobically, demonstrating that they were putative GAOs. Some of the Alphaproteobacteria were related to Defluvicoccus vanus (16 % of Bacteria), but the specific identity of many could not be determined by FISH. Further investigation into the identity of other GAOs is necessary.

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    ABSTRACT: Polyhydroxyalkanoate (PHA) production via mixed microbial cultures (MMCs) can potentially decrease process operational costs as compared to conventional pure culture techniques. However, the volumetric productivity of PHA by MMCs must be augmented to increase its cost competitiveness. For this purpose, a three-stage bioreactor system was operated in this study, with (i) anaerobic fermentation of molasses, (ii) culture selection, and (iii) PHA accumulation and harvesting stages. In stage 2, bioreactor operation with pH control at 8 led to twice the biomass concentration (up to 8 g VSS L−1, where VSS is the volatile suspended solids) as compared to operation without pH control (maximum pH 9). No loss in the specific PHA storage efficiency was observed (PHA content up to 57.5% and PHA storage rate up to 0.27 Cmol PHA Cmol X−1 h−1, where X is the active biomass), thereby resulting in twice the volumetric PHA production rate. The limited biomass growth at the higher pH level was not due to nutrient limitation, but likely to a shift in the microbial community. It is hypothesized that the increased enrichment of Azoarcus at pH 8 led to higher PHA productivity. pH control in the culture selection stage can lead to enhanced PHA production from MMCs, improving the viability of the process.
    Engineering in Life Sciences 11/2013; · 1.63 Impact Factor
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    ABSTRACT: This work studied the effect of the substrate feeding composition on the polyhydroxyalkanoate (PHA) accumulation capacity of an acetate enriched photosynthetic mixed culture (PMC). From the six tested organic acids-malate, citrate, lactate, acetate, propionate and butyrate-only the three volatile fatty acids (VFAs) enabled PHA production, with acetate and butyrate leading to polyhydroxybutyrate (PHB) formation and propionate leading to a HB:HV copolymer with a 51% fraction of hydroxyvalerate (HV). Also, results showed an acceleration of butyrate and propionate consumption when fed in the presence of acetate, suggesting that the latter can act as a co-substrate for butyrate and propionate uptake. Furthermore, results suggest that some PMC bacterial groups present a substrate preference for butyrate in relation to acetate and propionate. These findings indicate the possibility of feeding the PMC with cheap VFA rich fermented wastes, leading to a more cost-effective and environmentally sustainable PHA production system.
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