Potential of Bacillus sp. to produce polyhydroxybutyrate from biowaste.

AIM: To test the Bacillus strains for their abilities to produce polyhydroxybutyrate (PHB) from different sugars and biowaste (Pea-shells). METHODS AND RESULTS: Six Bacillus strains were checked for their ability to produce PHB from GM2 medium supplemented with different sugars at the rate of 1% (w/v) and from biowaste and GM2 (BW : M) combinations (3 : 7, 1 : 1, 7 : 3). Glucose supplemented GM2 medium resulted in maximum PHB production of 435 mg l(-1) constituting 31-62% w/w of the total cell dry mass. Substituting GM2 medium to the extent of 50% with biowaste (pea-shell slurry) resulted in 945-1205 mg l(-1) PHB (55-65% w/w). Optimization for additional nitrogen supplementation, inoculum size resulted in a final PHB production of 3010-3370 mg l(-1) equivalent to 300 g kg(-1) biowaste (dry wt). CONCLUSION: The Bacillus strains were able to produce PHB from biowaste (Pea-shells) as cheap source of substrate. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on usage of pea-shells as feed for PHB production, opening new possibilities for its use for production of PHB and Bacillus as potential candidate for the purpose.

Polyhydroxyalkanoates: an overview.

Polyhydroxyalkanoates have gained major importance due to their structural diversity and close analogy to plastics. These are gaining more and more importance world over. Different sources (natural isolates, recombinant bacteria, plants) and other methods are being investigated to exert more control over the quality, quantity and economics of poly(3-hydroxybutyrate) (PHB) production. Their biodegradability makes them extremely desirable substitutes for synthetic plastics. The PHB biosynthetic genes phbA, phbB and phbC are clustered and organized in one phbCAB operon. The PHB pathway is highly divergent in the bacterial genera with regard to orientation and clustering of genes involved. Inspite of this the enzymes display a high degree of sequence conservation. But how similar are the mechanisms of regulation of these divergent operons is as yet unknown. Structural studies will further improve our understanding of the mechanism of action of these enzymes and aid us in improving and selecting better candidates for increased production. Metabolic engineering thereafter promises to bring a feasible solution for the production of "green plastic".

Effect of some physiological factors on nitrogenase activity and nitrogenase mediated hydrogen evolution by mixed microbial culture.

Fermentative H2 evolution, nitrogenase activity (acetylene reduction) and nitrogenase mediated H2 evolution was studied in free cells of mixed microbial population of H2 producers. At 3% glucose level, the cells produced 8.35 l H2/mol glucose utilized. The role of nitrogenase system in H2 generation was evident by derepressed nitrogenase activity (0.46 nmoles C2H4 produced/mg protein/h) under defined in vitro conditions. For maximum expression of the activity, the cells required preactivation under anaerobic conditions by incubating at 40 degrees C for 20-24 h with 0.2% glucose in the culture medium. At an O2 level of more than 0.25%, the acetylene reduction activity decreased significantly and could not be detected at a level of 20%. Nitrogenase activity development was higher at acetylene: inoculum ratio between 4.2-6.25. H2 evolution was lower when the mixed cells were incubated under an atmosphere of 10% C2H2 and 5% CO gas. This decrease in H2 evolution was also evident at 2.5-6.5 mM NaNO3 and KNO3 concentrations in the liquid culture medium thus establishing more than 50% H2 evolution through nitrogenase.

Increased H2 production by immobilized microorganisms.

Viable cells of H2-producers (Bacillus licheniformis and a mixed microbial culture) were immobilized on brick dust and in calcium alginate beads. In batch culture, cells of the mixed culture in the free state yielded 8.2 l H2/mol glucose utilized, whereasB. licheniformis evolved 13.1 l H2. Immobilized cells, however, gave 4-fold more H2 than the free bacteria. Highest yields were from the cells immobilized on brick dust. High H2-production rates continued over two rounds of re-use of the immobilized cells.

Frementation of biowaste to H2 by Bacillus licheniformis.

Completely damaged wheat grains, unfit for human consumption, were fermented to H2 by Bacillus licheniformis strain JK1. Batch-culture fermentation of wheat slurries [6% (w/v) total solids and 5.8% (w/v) organic solids (OS)] evolved 225, 205 and 203 l of biogas-H, a mixture of H2, CO2 and H2S, per kg OS at pH 6, 7 and 8, respectively. H2 constituted 25% to 41% of the total biogas-H evolved. In single-stage continuous culture, H2 generated/kg OS reduced was 70 l at pH 6 and 74 l at pH 7 and 8.

Influence of the Bradyrhizobium japonicum Hydrogenase on the Growth of Glycine and Vigna Species.

The effect of the Bradyrhizobium japonicum hydrogenase on nitrogen fixation was evaluated by comparing the growth of Vigna and Glycine species inoculated with a Hup mutant and its Hup revertant. In all experiments, the growth of plants inoculated with the strain without hydrogenase was at least equal to the growth of the strain with hydrogenase. For Glycine usuriensis and Glycine max cv. Hodgson in liquid culture, the growth was higher with the Hup strain. It is possible that reduced rates of nitrogen fixation in the presence of hydrogenase are due to O(2) depletion caused by the hydrogen oxidizing, since the oxygen pressure in the air appears to be a limiting factor of symbiotic nitrogen fixation in the soybean.