Mild Alkaline Pretreatment of Rice Straw as a Feedstock in Microbial Fuel Cells for Generation of Bioelectricity.

The dependency on non-renewable fossil fuels as an energy source has drastically increased global temperatures. Their continuous use poses a great threat to the existing energy reserves. Therefore, the energy sector has taken a turn toward developing eco-friendly, sustainable energy generation by using sustainable lignocellulosic wastes, such as rice straw (RS). For lignocellulosic waste to be utilized as an efficient energy source, it needs to be broken down into less complex forms by pretreatment processes, such as alkaline pretreatment using NaOH. Varied NaOH concentrations (0.5%,1.0%,1.5%,2%) for alkaline pretreatment of RS were used for the holocellulose generation. Amongst the four NaOH concentrations tested, RS-1.5% exhibited higher holocellulose generation of 80.1%, whereas 0.5%, 1 5 and 2% pointed 71.9%, 73.8%, and 78.5% holocellulose generation, respectively. Further, microbial fuel cells (MFCs) were tested for voltage generation by utilizing holocellulose generated from untreated (RS-0%) and mildly alkaline pretreated RS (RS-1.5%) as a feedstock. The MFC voltage and maximum power generation using RS-0% were 194 mV and 167 mW/m2, respectively. With RS-1.5%, the voltage and maximum power generation were 556 mV and 583 mW/m2, respectively. The power density of RS-1.5% was three-fold higher than that of RS-0%. The increase in MFC power generation suggests that alkaline pretreatment plays a crucial role in enhancing the overall performance.

Phe-140 Determines the Catalytic Efficiency of Arylacetonitrilase from Alcaligenes faecalis.

Arylacetonitrilase from Alcaligenes faecalis ATCC8750 (NitAF) hydrolyzes various arylacetonitriles to the corresponding carboxylic acids. A systematic strategy of amino acid residue screening through sequence alignment, followed by homology modeling and biochemical confirmation was employed to elucidate the determinant of NitAF catalytic efficiency. Substituting Phe-140 in NitAF (wild-type) to Trp did not change the catalytic efficiency toward phenylacetonitrile, an arylacetonitrile. The mutants with nonpolar aliphatic amino acids (Ala, Gly, Leu, or Val) at location 140 had lower activity, and those with charged amino acids (Asp, Glu, or Arg) exhibited nearly no activity for phenylacetonitrile. Molecular modeling showed that the hydrophobic benzene ring at position 140 supports a mechanism in which the thiol group of Cys-163 carries out a nucleophilic attack on a cyanocarbon of the substrate. Characterization of the role of the Phe-140 residue demonstrated the molecular determinant for the efficient formation of arylcarboxylic acids.

Exploitation of Citrus Peel Extract as a Feedstock for Power Generation in Microbial Fuel Cell (MFC).

Microbial fuel cells (MFCs) are envisioned as an evolving cost-effective process for treating organic wastes to simultaneously generate bioelectricity. Therefore, in present study a single chambered mediator- less air cathode MFC was operated for bioelectricity generation using citrus waste (CW) as a feedstock. The MFC was operated at four organic loading conditions (OLs; 3, 6, 9 and 12 kg/m3). The voltage generation and organic content reduction demonstrated the possibility of utilizing CW as a substrate in MFC. The polarization analysis revealed a high-power generation of 71.1 mW/m2 with low OL of 3 kg/m3. The decrease in pH and high volatile fatty acids (VFAs) generation was noted at high OL. Our current findings suggest better performance of MFC, in terms of energy generation and organic reduction at high OL.

Enhanced production of pleuromutilin by Pleurotus mutilus and study on its molecular structure.

This study aims to enhance the accumulation of pleuromutilin by Pleurotus mutilus and to analyze the molecular structure of pleuromutilin. The results showed that a novel three-stage DO control strategy (60% DO, 1-3d; 45% DO, 4-6d; 30% DO, 7-9d) was very effective for improving the pleuromutilin accumulation and the highest production reached 12g/L, a 4-fold increase over a constant DO strategy. Furthermore, the flow behavior of fermentation broth appeared Newtonian with a maximum µap of 3.9×10-3Pa·s. Meanwhile the molecular formula (C22H34O5), molecular weight (378.5) and structural formula of pleuromutilin were concluded based on spectroscopy and element assay. The main components were hydroxyl, methyl, methylene, carbonyl, carboxyl, and polycyclic hydrocarbon. This work demonstrated that DO strategy was suitable for scalable production of pleuromutilin, which makes pleuromutilin more affordable as materials in food.

The metabolic flux regulation of Klebsiella pneumoniae based on quorum sensing system.

Quorum-sensing (QS) systems exist universally in bacteria to regulate multiple biological functions. Klebsiella pneumoniae, an industrially important bacterium that produces bio-based chemicals such as 2,3-butanediol and acetoin, can secrete a furanosyl borate diester (AI-2) as the signalling molecule mediating a QS system, which plays a key regulatory role in the biosynthesis of secondary metabolites. In this study, the molecular regulation and metabolic functions of a QS system in K. pneumoniae were investigated. The results showed that after the disruption of AI-2-mediated QS by the knockout of luxS, the production of acetoin, ethanol and acetic acid were relatively lower in the K. pneumoniae mutant than in the wild type bacteria. However, 2,3-butanediol production was increased by 23.8% and reached 54.93 g/L. The observed enhancement may be attributed to the improvement of the catalytic activity of 2,3-butanediol dehydrogenase (BDH) in transforming acetoin to 2,3-butanediol. This possibility is consistent with the RT-PCR-verified increase in the transcriptional level of budC, which encodes BDH. These results also demonstrated that the physiological metabolism of K. pneumoniae was adversely affected by a QS system. This effect was reversed through the addition of synthetic AI-2. This study provides the basis for a QS-modulated metabolic engineering study of K. pneumoniae.

The response of Serratia marcescens JG to environmental changes by quorum sensing system.

Many bacterial cells are known to regulate their cooperative behaviors and physiological processes through a molecular mechanism called quorum sensing. Quorum sensing in Serratia marcescens JG is mediated by the synthesis of autoinducer 2 (AI-2) which is a furanosyl borate diester. In this study, the response of quorum sensing in S. marcescens JG to environment changes such as the initial pH, carbon sources and boracic acid was investigated by a bioreporter and real-time PCR analysis. The results show that glucose can affect AI-2 synthesis to the greatest extent, and 2.0 % glucose can stimulate S. marcescens JG to produce more AI-2, with a 3.5-fold increase in activity compared with control culture. Furthermore, the response of quorum sensing to changes in glucose concentration was performed by changing the amount of luxS RNA transcripts. A maximum of luxS transcription appeared during the exponential growth phase when the glucose concentration was 20.0 g/L. AI-2 production was also slightly impacted by the low initial pH. It is significant for us that the addition of boracic acid at microdosage (0.1-0.2 g/L) can also induce AI-2 synthesis, which probably demonstrated the feasible fact that the 4,5-dihydroxy-2, 3-pentanedione cyclizes by the addition of borate and the loss of water, is hydrated and is converted to the final AI-2 in S. marcescens JG.