Dual function of ammonium acetate in acetone-butanol-ethanol fermentation by Clostridium acetobutylicum.

In this study, a compound nitrogen source, integrating the advantages of ammonium acetate and soybean meal, was proposed to further improve acetone-butanol-ethanol fermentation. Unfortunately, this compound nitrogen source was found to effectively inhibit cellular performance, as the introduction of NH4+ significantly decreased the yield of butanol and total solvents by 34.78% and 35.14%, to only 6.62 g/L and 10.76 g/L, respectively. Meanwhile, the regulatory mechanism was further elucidated at different levels. As a result, the NH4+ could down-regulate the transcriptional levels of key genes involved in butanol synthesis, and the activity of acetoacetyl-CoA/acyl-CoA transferase, and then decrease the accumulation of key intermediates. Therefore, ammonium acetate has a dual function in ABE fermentation, as it effectively improves ABE fermentation when it is the sole nitrogen source but significantly decreases fermentation performance in the presence of soybean meal, broadening the understanding of nitrogen regulation mechanism of C. acetobutylicum.

Isolation, purification and characterization of 5'-phosphodiesterase from Aspergillus fumigatus.

5'-Phosphodiesterase (5'-PDE) catalyzes the hydrolysis of ribonucleic acid to obtain a mixture of ribonucleotides, such as 5'-guanosine monophosphate and 5'-adenosine monophosphate. In this study, a 5'-PDE was newly isolated and purified from Aspergillus fumigatus. Following purification, this enzyme exhibited a specific activity of 1036.76 U/mg protein, a molecular weight of 9.5 kDa, and an optimal temperature and pH for enzyme activity of 60°C and 5.0, respectively. However, its activity was partially inhibited by Fe3+, Cu2+, and Zn2+, but slightly improved by the presence of K+ and Na+. Additionally, chemical-modification experiments were also applied to investigate the structural information of 5'-PDE, in which the residues containing carboxyl and imidazole groups were essential for enzyme activity based on their localization in the 5'-PDE active site. Furthermore, purified 5'-PDE could specifically catalyze the synthesis of ribonucleotides with a Vmax 0.71 mmol/mg·min and a KM of 13.60 mg/mL.

The industrial applications of cassava: current status, opportunities and prospects.

Cassava (Manihot esculenta Crantz) is a drought-tolerant, staple food crop that is grown in tropical and subtropical areas. As an important raw material, cassava is a valuable food source in developing countries and is also extensively employed for producing starch, bioethanol and other bio-based products (e.g. feed, medicine, cosmetics and biopolymers). These cassava-based industries also generate large quantities of wastes/residues rich in organic matter and suspended solids, providing great potential for conversion into value-added products through biorefinery. However, the community of cassava researchers is relatively small and there is very limited information on cassava. Therefore this review summarizes current knowledge on the system biology, economic value, nutritional quality and industrial applications of cassava and its wastes in an attempt to accelerate understanding of the basic biology of cassava. The review also discusses future perspectives with respect to integrating and utilizing cassava information resources for increasing the economic and environmental sustainability of cassava industries. © 2017 Society of Chemical Industry.

Microbial synthesis of poly-γ-glutamic acid: current progress, challenges, and future perspectives.

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made from repeating units of l-glutamic acid, d-glutamic acid, or both. Since some bacteria are capable of vigorous γ-PGA biosynthesis from renewable biomass, γ-PGA is considered a promising bio-based chemical and is already widely used in the food, medical, and wastewater industries due to its biodegradable, non-toxic, and non-immunogenic properties. In this review, we consider the properties, biosynthetic pathway, production strategies, and applications of γ-PGA. Microbial biosynthesis of γ-PGA and the molecular mechanisms regulating production are covered in particular detail. Genetic engineering and optimization of the growth medium, process control, and downstream processing have proved to be effective strategies for lowering the cost of production, as well as manipulating the molecular mass and conformational/enantiomeric properties that facilitate screening of competitive γ-PGA producers. Finally, future prospects of microbial γ-PGA production are discussed in light of recent progress, challenges, and trends in this field.