Simultaneous Production of MK-7 and Iturin A by Bacillus velezensis ND.

Bacillus velezensis can produce various secondary metabolites, such as the antibacterial compound iturin A and the coagulation-promoting menaquinone-7 (MK-7). To enhance the economic feasibility of the fermentation process, a co-production strategy, involving the simultaneous production of MK-7 and iturin A by Bacillus velezensis ND, was investigated in this study. Firstly, the effects of cultivation temperature and initial pH on the synthesis of MK-7 and iturin A were investigated. Considering the co-production of iturin A and MK-7, the optimal temperature and pH were determined as 32 °C and 7, respectively. Subsequently, important nutrients for the co-production process were investigated. It was observed that glycerol, soybean meal, yeast extract, and L-glutamate had a significant effect on the co-produce process. An optimal medium composed of glycerol (72.19 mL L-1), L-glutamate (1.4 g L-1), yeast extract (16.88 g L-1), and soybean meal (130.95 g L-1) was obtained by response surface methodology (RSM). This co-produce process was further scaled up in a biofilm reactor, and the maximum concentration of MK-7 and iturin A reached 46.88 mg L-1 and 5.58 g L-1, respectively. Finally, we established an effective method for separately extracting the two metabolites from the fermentation broth. The superiority of this co-production fermentation strategy demonstrates its significant potential for industrial production.

Process optimized for production of iturin A in biofilm reactor by Bacillus velezensis ND.

In this research, to provide an optimal growth medium for the production of iturin A, the concentrations of key amino acid precursors were optimized in shake flask cultures using the response surface method. The optimized medium were applied in a biofilm reactor for batch fermentation, resulting in enhanced production of iturin A. On this basis, a step-wise pH control strategy and a combined step-wise pH and temperature control strategy were introduced to further improve the production of iturin A. Finally, the fed-batch fermentation was performed based on combined step-wise pH and temperature control. The titer and productivity of iturin A reached 7.86 ± 0.23 g/L and 65.50 ± 1.92 mg/L/h, respectively, which were 37.65 and 65.20% higher than that before process optimization.

Light-induced expression of a novel marine laccase in Escherichia coli from Marinomonas profundimaris and its application in synthetic dye decolorization.

Laccases (EC 1.10.3.2) are green biocatalysts with a considerable potential in numerous environmental and industrial applications due to their abilities to oxidize a wide range of substrates, such as aromatic amines, while reducing molecular oxygen to water. In this study, a putative laccase, LacMp1, encoding a protein of 48.3 kDa and belonging to the Cu-oxidase_3 superfamily, was cloned and overexpressed in Escherichia coli with a light-induced expression system. High-level expression of recombinant protein LacMp1 was achieved under the light intensity of 6500 ± 200 lx from a white light-emitting diode (LED) belt. The purified LacMp1 showed high activity toward various laccase substrates, with the lowest Km value and highest kcat/Km value for syringaldazine at the optimal temperature and pH of 50 °C and 7.5. Dimethyl sulfoxide, ethanol, and metal ions such as Co2+, Ca2+, K+, Li+, Zn2+, Mn2+, Fe3+, and Ni2+ did not significantly inhibit the activity of LacMp1. Furthermore, LacMp1 showed tolerance to NaCl and kept 66.67 ± 2.24% of its initial activity at concentrations lower than 400 mM. Moreover, LacMp1 exhibited wide-spectrum decolorization ability towards indigoid, anthraquinonic, and azo dyes without the aid of redox mediators at pHs ranging from 5.0 to 9.0. It decolorized 99.83 ± 0.12% of indigo carmine, 99.54 ± 0.43% of Congo red, 88.41 ± 3.22% of Eriochrome black T, and 51.61 ± 1.82% of Reactive blue 4, respectively. These unusual properties demonstrated that LacMp1 had potential in specific industrial or environmental applications.