Aims: To search for new bacteria for efficient production of polyhydroxyalkanoates (PHAs) from glycerol.
Methods and results: Samples were taken from different environments in Germany and Egypt, and bacteria capable of growing in mineral salts medium with glycerol as sole carbon source were enriched. From a wastewater sediment sample in Egypt, a Gram-negative bacterium (strain MW1) was isolated that exhibited good growth and that accumulated considerable amounts of polyhydroxybutyrate (PHB) from glycerol and also from other carbon sources. The 16S rRNA gene sequence of this isolate exhibited 98.5% and 96.2% similarity to Zobellella denitrificans strain ZD1 and to Zobellella taiwanensis strain ZT1 respectively. The isolate was therefore affiliated as strain MW1 of Z. denitrificans. Strain MW1 grows optimally on glycerol at 41 degrees C and pH 7.3 and accumulated PHB up to 80.4% (w/w) of cell dry weight. PHB accumulation was growth-associated. Although it was not an absolute requirement, 20 g l(-1) sodium chloride enhanced both growth (5 g cell dry weight per litre) and PHB content (87%, w/w). Zobellella denitrificans strain MW1 is also capable to accumulate the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer if sodium propionate was used as cosubstrate in addition to glycerol.
Conclusions: A new PHB-accumulating strain was isolated and identified. This strain is able to utilize glycerol for growth and PHB accumulation to high content especially in the presence of NaCl that will enable the utilization of waste glycerol from biodiesel industry.
Significance and impact of the study: This study is the first report on accumulation of PHA in a member of the new genus Zobellella. Furthermore, utilization of glycerol as the sole carbon source for fast growth and PHB biosynthesis, growth in the presence of NaCl and high PHB contents of the cells will make this newly isolated bacterium a potent candidate for industrial production of PHB from crude glycerol occurring as byproduct during biodiesel production.