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Industrial production of biodegradable polyesters such as polyhydroxyalkanoates is hampered by high production costs, among which the costs for substrates and for downstream processing represent the main obstacles. Inexpensive fermentable raw materials such as crude glycerol, an abundant by-product of the biodiesel industry, have emerged to be promising carbon sources for industrial fermentations. In this study, Zobellella denitrificans MW1, a recently isolated bacterium, was used for the production of poly(3-hydroxybutyrate) (PHB) from glycerol as the sole carbon source. Pilot-scale fermentations (42-liter scale) were conducted to scale up the high PHB accumulation capability of this strain. By fed-batch cultivation, at first a relatively high cell density (29.9 ؎ 1.3 g/liter) was obtained during only a short fermentation period (24 h). However, the PHB content was relatively low (31.0%

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°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.

Fermentations, which are performed with thermophilic microorganisms, are energy-efficient processes because few cooling efforts are necessary. Moreover, thermophilic fermentations are self-heated systems because the heat generated by the cell's metabolism during high-cell-density (HCD) growth (28, 49) and also by stirring can be used for providing heat to the fermentation process itself. Thus, both heating and cooling costs are lowered (14, 46). Additionally, unlike when mesophilic bacteria are used in fermentations, sterile conditions may not be essential during a process involving thermophilic bacteria (41, 42).Unfortunately, thermophiles usually grow to only low cell densities. Recently, with the use of advanced fermentation technology, a few thermophilic bacteria were cultivated successfully, yielding HCD growth and enhanced product formation (15,25). In industry, HCD cultivation is often a prerequisite for high productivity during fermentations, in particular if intracellular compounds are being produced. HCD cultivations are enhanced cultivations of the microbial strain achieving cell dry weight (CDW) concentrations exceeding 100 g/liter. However, a lower cell density can be regarded as an HCD as well, depending on the microorganism and its cultivation conditions (39). In general, HCD cultivations represent a 10-to 20-fold increase in growth in comparison to normal cell density growth. Problems encountered by HCD cultivation are numerous, such as partial O 2 pressure (pO 2 ) deficiency, byproduct formation, and/or metabolic heat production. As a result of the growing industrial interest in HCD, many attempts have been made to develop HCD fermentations, for example, by improving potent strains and/or using different types of bioreactors and cultivation strategies (39).The most industrially applicable technique is fed-batch fer-

Aims: This study aimed at isolating thermophilic bacteria that utilize cheap carbon substrates for the economically feasible production of poly(3-hydroxybutyrate), poly(3HB), at elevated temperatures. Methods and Results: Thermophilic bacteria were enriched from an aerobic organic waste treatment plant in Germany, and from hot springs in Egypt. Using the viable colony staining method for hydrophobic cellular inclusions with Nile red in mineral salts medium (MSM) containing different carbon sources, six Gram-negative bacteria were isolated. Under the cultivation conditions used in this study, strains MW9, MW11, MW12, MW13 and MW14 formed stable star-shaped cell-aggregates (SSCAs) during growth; only strain MW10 consisted of free-living rod-shaped cells. The phylogenetic relationships of the strains as derived from 16S rRNA gene sequence comparisons revealed them as members of the Alphaproteobacteria. The 16S rRNA gene sequences of the isolates were very similar (> 99% similarity) and exhibited similarities ranging from 93 to 99% with the most closely related species that were Chelatococcus daeguensis, Chelatococcus sambhunathii,Chelatococcus asaccharovorans, Bosea minatitlanensis, Bosea thiooxidans and Methylobacterium lusitanum. Strains MW9, MW10, MW13 and MW14 grew optimally in MSM with glucose, whereas strains MW11 and MW12 preferred glycerol as sole carbon source for growth and poly(3HB) accumulation. The highest cell density and highest poly(3HB) content attained were 4 center dot 8 g l-l (cell dry weight) and 73% (w/w), respectively. Cells of all strains grew at temperatures between 37 and 55 degrees C with the optimum growth at 50 degrees C. Conclusions: New PHA-accumulating thermophilic bacterial strains were isolated and characterized to produce poly(3HB) from glucose or glycerol in MSM at 50 degrees C. SSCAs formation was reported during growth. Significance and Impact of the Study: To the best of our knowledge, this is the first report on the formation of SSCAs by PHA-accumulating bacteria and also by thermophilic bacteria. PHA-producing thermophiles can significantly reduce the costs of fermentative PHA production