Iron effect on the fermentative metabolism of Clostridium acetobutylicum ATCC 824 using cheese whey as substrate

Butanol is considered a superior liquid fuel that can replace gasoline in internal combustion engines. It is produced by acetone-butanol-ethanol (ABE) fermentation using various species of solventogenic clostridia. Performance of ABE fermentation process is severely limited mostly by high cost of substrate, substrate inhibition and low solvent tolerance; leading to low product concentrations, low productivity, low yield, and difficulty in controlling culture metabolism. In order to decrease the cost per substrate and exploit a waste generated by dairy industry, this study proposes using cheese whey as substrate for ABE fermentation. It was observed that the addition of an iron source was strictly necessary for the cheese whey to be a viable substrate because this metal is needed to produce ferredoxin, a key protein in the fermentative metabolism of Clostridium acetobutylicum serving as a temporary electron acceptor. Lack of iron in the cheese whey impedes ferredoxin synthesis and therefore, restricts pyruvate-ferredoxin oxidoreductase activity leading to the production of lactic acid instead of acetone, butanol and ethanol. Moreover, the addition of FeSO4 notably improved ABE production performance by increasing butanol content (7.13 ± 1.53 g/L) by 65% compared to that of FeCl3 (4.32 ± 0.94 g/L) under the same fermentation conditions

Laccase-luminol chemiluminescence system: an investigation of substrate inhibition

Chemiluminescence (CL) reactions are widely used for the detection and quantification of many types of analytes. Laccase has previously been proposed in CL reactions; however, its light emission behaviour has not been characterized. This study was conducted to characterize the laccase-luminol system, determine its kinetic parameters, and analyze the effects of protein and OH- concentration on the CL signal. Laccase from Coriolopsis gallica was combined with different concentrations of luminol (125 nM to 4 mM), and the enzyme kinetics were evaluated using diverse kinetic models. The laccase-luminol system was able to produce CL without an intermediate molecule, but it exhibited substrate-inhibition behaviour. A two-site random model was used and suggested that when the first luminol molecule was bound to the active site, laccase affinity for the second luminol molecule was increased. This inhibition effect could be avoided using a low luminol concentration. At 5 μM luminol concentration, 1 mg/ml (0.13 U) laccase is needed to achieve nearly 90% of the maximum CL signal, suggesting that the available luminol could not bind to all active sites. Furthermore, the concentration of NaOH negatively affected the CL signal. The laccase-luminol system represents an alternative to existing CL systems, with potential uses in molecular detection and quantification.Translational Omics and Bioengineering and Regenerative Medicine strategic focus groups of Tecnologico de Monterrey; CONACyT, Grant/Award Number: 492276With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Osmolyte Signatures for the Protection of Aspergillus sydowii Cells under Halophilic Conditions and Osmotic Shock

Aspergillus sydowii is a moderate halophile fungus extensively studied for its biotechnological potential and halophile responses, which has also been reported as a coral reef pathogen. In a recent publication, the transcriptomic analysis of this fungus, when growing on wheat straw, showed that genes related to cell wall modification and cation transporters were upregulated under hypersaline conditions but not under 0.5 M NaCl, the optimal salinity for growth in this strain. This led us to study osmolyte accumulation as a mechanism to withstand moderate salinity. In this work, we show that A. sydowii accumulates trehalose, arabitol, mannitol, and glycerol with different temporal dynamics, which depend on whether the fungus is exposed to hypo- or hyperosmotic stress. The transcripts coding for enzymes responsible for polyalcohol synthesis were regulated in a stress-dependent manner. Interestingly, A. sydowii contains three homologs (Hog1, Hog2 and MpkC) of the Hog1 MAPK, the master regulator of hyperosmotic stress response in S. cerevisiae and other fungi. We show a differential regulation of these MAPKs under different salinity conditions, including sustained basal Hog1/Hog2 phosphorylation levels in the absence of NaCl or in the presence of 2.0 M NaCl, in contrast to what is observed in S. cerevisiae. These findings indicate that halophilic fungi such as A. sydowii utilize different osmoadaptation mechanisms to hypersaline conditions