No abstract

An extracellular tannase (tannin acyl hydrolase) was isolated from Paecilomyces variotii and purified from cell-free culture filtrate using ammonium sulfate precipitation followed by ion exchange and gel filtration chromatography. Fractional precipitation of the culture filtrate with ammonium sulfate yielded 78.7% with 13.6-folds purification, and diethylaminoethyl-cellulose column chromatography and gel filtration showed 19.4-folds and 30.5-folds purifications, respectively. Molecular mass of tannase was found 149.8 kDa through native polyacrylamide gel electrophoresis (PAGE) analysis. Sodium dodecyl sulphate-PAGE revealed that the purified tannase was a monomeric enzyme with a molecular mass of 45 kDa. Temperature of 30 to 50 degrees C and pH of 5.0 to 7.0 were optimum for tannase activity and stability. Tannase immobilized on alginate beads could hydrolyze tannic acid even after extensive reuse and retained about 85% of the initial activity. Thin layer chromatography, high performance liquid chromatography, and (1)H-nuclear magnetic resonance spectral analysis confirmed that gallic acid was formed as a byproduct during hydrolysis of tannic acid.

No abstract

A modeling study was conducted on growth kinetics of three different strains of Pseudomonas spp. (Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putida) during benzene degradation to determine optimum substrate concentrations for most efficient biodegradation. Batch tests were performed for eight different initial substrate concentrations to observe cell growth and associated substrate degradation using benzene-adapted cells. Kinetic parameters of both inhibitory (Haldane-Andrews, Aiba-Edwards) and noninhibitory (Monod) models were fitted to the relationship between specific growth rate and substrate concentration obtained from the growth curves. Results showed that half-saturation constant of P. fluorescens was the highest among the three strains, indicating that this strain could grow well at high concentration, while P. putida could grow best at low concentration. The inhibition constant of P. aeruginosa was the highest, implying that it could tolerate high benzene concentration and therefore could grow at a wider concentration range. Estimated specific growth rate of P. putida was lower, but half-saturation constant was higher than those from literature study due to high substrate concentration range used in this study. These two kinetic parameters resulted in substantial difference between Monod- and Haldane-type models, indicating that distinction should be made in applying those models.

No abstract

No abstract

No abstract

Aerobic granules offer enhanced biological nutrient removal and are compact and dense structures resulting in efficient settling properties. Granule instability, however, is still a challenge as understanding of the drivers of instability is poorly understood. In this study, transient instability of aerobic granules, associated with filamentous outgrowth, was observed in laboratory-scale sequencing batch reactors (SBRs). The transient phase was followed by the formation of stable granules. Loosely bound, dispersed, and pinpoint seed flocs gradually turned into granular flocs within 60 days of SBR operation. In stage 1, the granular flocs were compact in structure and typically 0.2 mm in diameter, with excellent settling properties. Filaments appeared and dominated by stage 2, resulting in poor settleability. By stage 3, the SBRs were selected for larger granules and better settling structures, which included filaments that became enmeshed within the granule, eventually forming structures 2-5 mm in diameter. Corresponding changes in sludge volume index were observed that reflected changes in settleability. The protein-to-polysaccharide ratio in the extracted extracellular polymeric substance (EPS) from stage 1 and stage 3 granules was higher (2.8 and 5.7, respectively), as compared to stage 2 filamentous bulking (1.5). Confocal laser scanning microscopic (CLSM) imaging of the biomass samples, coupled with molecule-specific fluorescent staining, confirmed that protein was predominant in stage 1 and stage 3 granules. During stage 2 bulking, there was a decrease in live cells; dead cells predominated. Denaturing gradient gel electrophoresis (DGGE) fingerprint results indicated a shift in bacterial community composition during granulation, which was confirmed by 16S rRNA gene sequencing. In particular, Janthinobacterium (known denitrifier and producer of antimicrobial pigment) and Auxenochlorella protothecoides (mixotrophic green algae) were predominant during stage 2 bulking. The chitinolytic activity of Chitinophaga is likely antagonistic towards Auxenochlorella and may have contributed to stage 3 stable granule formation. Rhodanobacter, known to support complete denitrification, were predominant in stage 1 and stage 3 granules. The relative abundance of Rhodanobacter coincided with high protein concentrations in EPS, suggesting a role in microbial aggregation and granule formation.