Isolation, production and optimization of endogenous alkaline protease from in-situ sludge and its evaluation as sludge hydrolysis enhancer

Genetic Modification of Aurantiochytrium sp. 18W-13a for Enhancement of Proteolytic Activity by Heterologous Expression of Extracellular Proteases

A marine thraustochytrid, Aurantiochytrium, is a promising organism to produce docosahexaenoic acid (DHA) and squalene. Utilization of inexpensive substances such as proteins in wastes and by-products from the food industry for cultivation is a considerable option to reduce production cost; however, the proteolytic ability of Aurantiochytrium spp. is low compared to taxonomically close Shizochytrium aggregatum. We previously identified extracellular protease (extracellular protease 1, EP1) in S. aggregatum ATCC 28209 from the supernatant of the culture and found that a similar protease gene (EP2) was located downstream of the EP1 gene. In the present study, we created the transformants expressing SaEP1 and/or SaEP2 to enhance the proteolytic ability of Aurantiochytrium sp. 18W-13a strain and cultivated them in the medium containing casein as a test protein substrate. Through SDS-PAGE analysis, we confirmed that casein in the supernatant was more efficiently degraded by the transformants than the wild type, suggesting that the expressed protease(s) were properly expressed and excreted. After 4-day cultivation in the casein medium, the value of optical density at 660 nm and the cell number in the culture of the transformant that expressed both SaEP1 and SaEP2 (designated as EP12 strain) showed 1.48- and 1.38-fold higher than those of wild type, respectively. The DHA and squalene yield of the EP12 strain were respectively 158.3 and 0.23 mg L-1, and these values were 1.42- and 2.01-fold higher than those of wild type, respectively, suggesting that the EP12 created in the present study is a favorable strain for the cultivation using protein-containing medium.

Newly isolated lysozyme-producing strain Proteus mirabilis sp. SJ25 reduced the waste activated sludge: Performance and mechanism

To promote aerobic digestion of sludge, a lysozyme-producing strain was screened and identified as Proteus mirabilis sp. SJ25. The results of response surface methodology (RSM) showed that at the temperature of 30.8 °C, pH of 6.69, and the inoculum amount of 2.81%, the sludge reduced by 26.58%. Compared with the control group, the removal efficiency of suspended solids (SS) from sludge in the experimental group increased by 14.60%, the release of soluble chemical oxygen demand (SCOD) increased by 2.21 times, and the release of intracellular substances increased significantly. Actinobacteriota, Chloroflexi, Proteobacteria, Bacteroidota, and Firmicutes were the main phyla involved in the sludge reduction process. Strain SJ25 enhanced the degradation rate of sludge by releasing lysozyme lysis to lyse bacteria, enhancing the metabolism and membrane transport of carbohydrates and amino acids. This study provides a new perspective in the field of efficient degradation of waste sludge.

Process efficiency in relation to enzyme pre-treatment duration in black soldier fly larvae composting

Black soldier fly larvae (BSFL) composting is a treatment in which biodegradable food waste is converted into animal-feed protein and organic fertiliser. BSFL composting has greatest potential for mixed food waste, but under European Union regulations only plant-based waste is permitted as feed for larvae. Biomass conversion efficiency (BCE) in BSFL composting is lower for plant-based waste than for mixed food waste. One way of improving BCE for plant-based waste is to add enzymes to make the waste more available to the larvae, but enzyme pre-treatment is not commonly applied prior to BSFL composting. Therefore this study examined the impact of enzyme pre-treatment duration on process efficiency in BSFL composting of lettuce-cabbage waste pre-treated with enzymes for 0-4 days. The results showed that total solids (TS) in larvae decreased with longer enzyme pre-treatment. Direct addition of enzymes at the start of BSFL treatment (0 day pre-treatment) resulted in 22% higher BCE on a volatile solids (VS) basis compared with the control, while longer pre-treatment did not improve BCE further. Much of the VS was respired in the 0-day pre-treatment, resulting in lower mass of residues at the end of treatment. Longer pre-treatment increased microbial respiration, suggesting that the microbial community consumed more easily available carbohydrates during the pre-treatment step, which counteracted the purpose of enzyme pre-treatment, i.e. increasing BCE during BSFL composting.