The effect of temperature on the microbial community structure has been hardly investigated. However, both of these studies mainly studied the influence of temperature on the kinetics of the process. The temperature effects on PHA-producing cultures enriched with a feast-famine strategy have been studied by Krishna and van Loosdrecht, 1999 and by Johnson et al., 2010. A thorough understanding of this competition principle would be essential for a commercial success of bioplastic production from waste. acidivorans with other bacterial species during the enrichment step was not performed. However, a detailed evaluation on the effect of temperature and cycle length on the competition of P. The temperature and the cycle length have been proposed to have a direct impact. The key factors responsible for enrichment of P. acidivorans mixed culture was initially enriched in a sequencing batch reactor (SBR) operated under carbon limitation, at 1 day solid retention time (SRT) and hydraulic retention time, at temperature of 30° C and a 12 h cycle length. Molecular, biological and microbiological analyses showed that a novel bacterium Plasticicumulans acidivorans (Jiang et al., submitted) was the dominant PHB-producing bacterium in this enrichment. Recently, enrichment of bacteria with a maximum polyhydroxybutyrate (PHB) content of 89% cell dry weight has been achieved by Johnson et al., 2009a.
Extensive efforts are, therefore being made to improve the PHA content of mixed cultures ( Dias et al., 2006). This increases the relative costs for downstream processing, and thereby increases the production costs of PHA ( Mudliar et al., 2008). However, the maximum PHA content of mixed cultures is in general lower than that of pure cultures ( Reis et al., 2003 Dias et al., 2006). A two-step process with a feast-famine regime has been demonstrated to enable the effective enrichment of a PHA-producing mixed microbial culture from the natural environment based on the ecological role of PHA ( van Loosdrecht, 2000). This process aims at using non-sterile equipment and wastewater as a substrate, combining wastewater treatment and bioplastic production. To reduce the price of bioplastics, the production of PHAs by mixed microbial cultures has been investigated ( Kleerebezem and van Loosdrecht, 2007). However, the use of sterile equipment, defined substrates and downstream processing contribute to the high costs of PHA production, which limits the industrial application of PHA ( Keshavarz and Roy, 2010). In addition to natural producers, genetically-modified organisms are used for the industrial production of PHA ( Slater et al., 1988 Braunegg et al, 1998). Since the first discovery of PHA production in Bacillus megaterium by Lemoigne, 1926, over 250 different types of bacteria have been reported as natural PHA producers ( Steinbüchel, 1991). Polyhydroxyalkanoates (PHAs) are biodegradable bioplastics that can be produced by bacteria from renewable resources ( Kleerebezem and van Loosdrecht, 2007 Keshavarz and Roy, 2010). These results suggest that to establish enrichment with the capacity to store a high fraction of PHB, the number of cycles per SRT should be minimized independent of the temperature. The PHB content at the end of the feast phase correlated well with the cycle length at a constant solid retention time (SRT). Incomplete PHB degradation limited biomass growth and allowed Zoogloea to outcompete P. This is particularly true for the PHB degradation, resulting in incomplete PHB degradation in P. acidivorans was more temperature sensitive as compared with Zoogloea.
Short-term temperature change experiments revealed that P. Both enrichments accumulated PHB more than 75% of cell dry weight.
Zoogloea and Plasticicumulans acidivorans dominated the SBRs operated at 20 ☌ and 30 ☌, respectively. In this study, the microbial community structure of the PHB-producing enrichments was found to be strongly dependent on temperature, but not on cycle length. The impact of temperature and cycle length on microbial competition between polyhydroxybutyrate (PHB)-producing populations enriched in feast-famine sequencing batch reactors (SBRs) was investigated at temperatures of 20 ☌ and 30 ☌, and in a cycle length range of 1–18 h.