Cloning, expression, and characterization of an acetate kinase from a high rate of biohydrogen bacterial strain Ethanoligenens sp. hit B49

Elevated acetate kinase (ackA) gene expression, activity, and biofilm formation observed in methicillin-resistant strains of Staphylococcus aureus (MRSA)

BACKGROUND

Staphylococcus aureus spreads its infections through biofilms. This usually happens in the stationary phase of S. aureus growth where it utilizes accumulated acetate as a carbon source via the phosphotrans-acetylase-acetate kinase (Pta-Ack) pathway. In which acetate kinase (ackA) catalyzes the substrate-level phosphorylation, a vital secondary energy-yielding pathway that promotes biofilms formation aids bacterium survival in hostile environments. In this study, we describe the cloning, sequencing, and expression of S. aureus ackA gene. The expression analysis of ackA gene in methicillin-resistant strains of S. aureus (MRSA) correlates with ackA activity and biofilm units. The uniqueness of ackA was analyzed by using in silico methods.

RESULTS

Elevated ackA gene expression was observed in MRSA strains, which correlates with increased ackA activity and biofilm units, explaining ackA role in MRSA growth and pathogenicity. The pure recombinant acetate kinase showed a molecular weight of 44 kDa, with enzyme activity of 3.35 ± 0.05 μM/ml/min. The presence of ACKA-1, ACKA-2 sites, one ATP, and five serine/threonine-protein kinase sites in the ackA gene (KC954623.1) indicated that acetyl phosphate production is strongly controlled. The comparative structural analysis of S. aureus ackA with ackA structures of Mycobacterium avium (3P4I) and Salmonella typhimurium (3SLC) exhibited variations as indicated by the RMSD values 1.877 Å and 2.141 Å respectively, explaining why ackA functions are differently placed in bacteria, concurring its involvement in S. aureus pathogenesis.

CONCLUSIONS

Overall findings of this study highlight the correlation of ackA expression profoundly increases survival capacity through biofilm formation, which is a pathogenic factor in MRSA and plays a pivotal role in infection spreading.

Biohydrogen production from anaerobic fermentation

Significant progress has been achieved in China for biohydrogen production from organic wastes, particularly wastewater and agricultural residues, which are abundantly available in China. This progress is reviewed with a focus on hydrogen-producing bacteria, fermentation processes, and bioreactor configurations. Although dark fermentation is more efficient for hydrogen production, by-products generated during the fermentation not only compromise hydrogen production yield but also inhibit the bacteria. Two strategies, combination of dark fermentation and photofermentation and coupling of dark fermentation with a microbial electrolysis cell, are expected to address this issue and improve hydrogen production as well as substrate utilization, which are also discussed. Finally, challenges and perspectives for biohydrogen production are highlighted.

Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment

This paper offers an effective pretreatment method that can simultaneously achieve excess sludge reduction and bio-hydrogen production from sludge self-fermentation. Batch tests demonstrated that the combinative use of ozone/ultrasound pretreatment had an advantage over the individual ozone and ultrasound pretreatments. The optimal condition (ozone dose of 0.158 g O(3)/g DS and ultrasound energy density of 1.423 W/mL) was recommended by response surface methodology. The maximum hydrogen yield was achieved at 9.28 mL H(2)/g DS under the optimal condition. According to the kinetic analysis, the highest hydrogen production rate (1.84 mL/h) was also obtained using combined pretreatment, which well fitted the predicted equation (the squared regression statistic was 0.9969). The disintegration degrees (DD) were limited to 19.57% and 46.10% in individual ozone and ultrasound pretreatments, while it reached up to 60.88% in combined pretreatment. The combined ozone/ultrasound pretreatment provides an ideal and environmental friendly solution to the problem of sludge disposal.

Optimization of culture conditions for hydrogen production by Ethanoligenens harbinense B49 using response surface methodology

The design of an optimum and cost-efficient medium for high-level production of hydrogen by Ethanoligenens harbinense B49 was attempted by using response surface methodology (RSM). Based on the Plackett-Burman design, Fe(2+) and Mg(2+) were selected as the most critical nutrient salts. Subsequently, the optimum combination of the selected factors and the sole carbon source glucose were investigated by the Box-Behnken design. Results showed that the maximum hydrogen yield of 2.21 mol/mol glucose was predicted when the concentrations of glucose, Fe(2+) and Mg(2+) were 14.57 g/L, 177.28 mg/L and 691.98 mg/L, respectively. The results were further verified by triplicate experiments. The batch reactors were operated under an optimized condition of the respective glucose, Fe(2+) and Mg(2+) concentration of 14.5 g/L, 180 mg/L and 690 mg/L, the initial pH of 6.0 and experimental temperature of 35+/-1(o)C. Without further pH adjustment, the maximum hydrogen yield of 2.20 mol/mol glucose was obtained based on the optimized medium with further verified the practicability of this optimum strategy.