Polyhydroxyalkanoates (PHAs) are interesting as material for bioplastic production because they are recognized as biodegradable and could be produced from renewable resources. The industrial production of PHAs has already been used in practice by pure cultures. In recent years, many studies have been addressed of PHA production by mixed cultures. Nevertheless, while fermentation strategy to improve the PHA content of biomass, yield and productivity in pure cultures are well defined, knowledge about the operational condition for PHA synthesis by mixed culture is still very limited. The ecology of the microbial community of activated sludge remains largely unknown, primarily because of the difficulty of making detailed observation. Recently, developed molecular techniques allow determination of community composition from DNA extracted directly from biomass samples. This study examined the changes of bacterial communities in activated sludge through application of the molecular technique, ribosomal intergenic spacer analysis (RISA). Microbial communities from anaerobic-aerobic and ammonia limited fermentations were ascertained. The applied operational conditions were shown to select for a restricted microbial population, which were different in term of structure with respect to the initial microbial consortia in the activated sludge used as inoculum.
Polyhydroxyalkanoates (PHAs) are especially interesting because of their similar properties to synthetic plastics and their potential use as biodegradable polymers. Many strategies have been employed to effectively and economically produce PHAs, among them a production process based on mixed microbial populations, enriched from activated sludge could be one of the alternative technologies. Defining the bacterial species creating these anonymous populations is crucial for the improvement of cultivation strategy. Moreover, enriched bacterial populations could be a promising source for microbes, useful in many biotechnological projects. The main object of this study was to characterize the microorganisms creating the microbial consortium cultured towards PHAs production. After cultivation, bacteria were identified using the 16S rRNA gene sequencing approach. The presence of genes engaged in PHAs synthesis was detected using PCR. The performed analysis revealed that among eleven isolated bacterial strains, four possessed the ability of polyhydroxybutyrate synthesis.
Biosynthesis of biodegradable polymers polyhydroxyalkanotes (PHAs) have been studied extensively in wild type and genetically modified prokaryotic cells, however the content and structure of PHAs in wild type yeasts is not well documented. The purpose of this study was to screen yeast isolates collected from different ecosystems for their ability to accumulate PHAs. Identification of the isolates and characterization of PHAs produced by the positive isolates were investigated. One positive isolate (strain Y4) was identified by both API20C system and 18S rDNA sequencing. The data revealed that isolate Y4 belongs to the yeast genus Rhodotorula and exhibits 18S rDNA similarity value >99% to the species Rhodotorula minuta. Quantification of PHAs yield of strain Y4 in glucose, oleic acid and tween 60 containing medium for over a growth period of 96 h gave 2% of PHAs in biomass. The nature of produced PHAs was analyzed by infrared spectroscopy and nuclear magnetic resonance (¹H and ¹³C NMR) and found to contain polyhydroxybutyrate and polyhydroxyvalerate (PHBV).