Conversion of waste cooked rice into maltose by a Bacillus subtilis-derived maltogenic amylase and production of maltobionic acid from the prepared maltose using genetically modified Pseudomonas taetrolens.

In this study, we attempted to produce maltobionic acid (MBA) from waste cooked rice (WCR) using maltose as an intermediate. In our previous study, we produced maltose from WCR using a commercial maltogenic amylase (Maltogenase L). However, in the present study, we used wild-type Bacillus subtilis, which inherently produces maltogenic amylase (AmyE), instead of Maltogenase L to produce maltose from WCR. During cultivation of B. subtilis with WCR, maltose was successfully produced by AmyE in the culture medium. To improve maltose production, we constructed a recombinant B. subtilis strain expressing AmyE and used it for maltose production. Following cultivation of the recombinant B. subtilis strain, the maltose production titer (34.6 g/L) increased approximately 3.6-fold that (9.6 g/L) obtained from the cultivation of wild-type B. subtilis. Using Pseudomonas taetrolens, an efficient MBA-producing bacterium, 28.8 g/L of MBA was produced from the prepared maltose (27.6 g/L). The above results indicated that MBA was successfully produced from WCR via a two-step process, which involved the conversion of WCR into maltose by maltogenic amylase-producing B. subtilis and the production of MBA from the WCR-derived maltose by P. taetrolens.

Enhanced production of maltobionic acid by a metabolically engineered Escherichia coli incapable of maltose utilization.

To produce maltobionic acid (MBA) from maltose in Escherichia coli, we recombinantly expressed a glucose dehydrogenase gene (gdh1) from Enterobacter cloacae and a pyrroloquinoline quinone (PQQ) synthesis gene cluster (pqqFABCDEMIH) from Pseudomonas taetrolens. Although the recombinant E. coli strain (E. coli [pKK-ECGDH1 + pACYC-PQQ]) successfully produced MBA from maltose, the yield of MBA was rather low, indicating that E. coli has other maltose utilization pathways. Amylomaltase (MalQ) is the first enzyme in the maltose utilization pathway in E. coli. To investigate the potential role of MalQ on MBA production, E. coli malQ was inactivated. The culturing of the recombinant E. coli strain (E. coli ∆malQ [pKK-ECGDH1 + pACYC-PQQ]) in a flask resulted in higher MBA production titer, yield, and productivity (209.3 g/L, 100%, and 1.1 g/L/h, respectively) than those of E. coli [pKK-ECGDH1 + pACYC-PQQ] (162.1 g/L, 77.4%, and 0.5 g/L/h, respectively), indicating that the MalQ inactivation was highly effective in improving the MBA production ability of E. coli. After fermentation using 5-L bioreactor, MBA production titer, yield, and productivity of the recombinant E. coli strain were 209.3 g/L, 100%, and 1.5 g/L/h, respectively, which were 1.3-, 1.3-, 2.3-fold higher than those of E. coli [pKK-ECGDH1 + pACYC-PQQ] (167.3 g/L, 79.9%, and 0.65 g/L/h), respectively. Thus, our results provide an important foundation for efficient MBA production using recombinant E. coli strain.

Improving the Utilization of Food Waste: Conversion of Food Waste into Residual Food Dried Substance and Use of This Material as a Culture Nutrient for Microbial Production of Lactic Acid.

To reduce food waste (FW) disposal costs, many Koreans now convert FW into residual food dried substances (RFDS) using a house-service food drying machine and then dispose of the RFDS. To recycle RFDS, we tested whether RFDS could be used as a culture nutrient to produce value-added microbial chemicals. As a case study, we attempted to produce lactic acid (LA) by cultivating lactic acid bacteria using RFDS. To prepare the culture medium for LA production, we finely ground the RFDS and dissolved it with CaCO3, a pH-controlling agent. Six lactic acid bacteria were tested to improve LA production, with Lactococcus lactis showing the highest LA production. To enhance LA production, three hydrolytic enzymes, amylase, protease, and lipase, were introduced separately or simultaneously into the RFDS medium during the cultivation of the L. lactis strain. The addition of amylase alone was the most effective in increasing LA production. We then investigated the effect of the RFDS concentration on LA production. The highest LA production was achieved when 100 g/L of RFDS was used. LA production was scaled up using a 5 L bioreactor. During the fermentation, LA production improved to 46.32 g/L, which was 1.73-fold higher than that (26.83 g/L) obtained from the flask culture. These results show that RFDS from FW can be used as a culture nutrient to produce LA. Our study provides a new and simple FW recycling method and lays the foundation for expanding the usability of FW.

Cause of postoperative mortality in patients with end-stage renal disease.

BACKGROUND: The number of patients with end-stage renal disease (ESRD) who are dependent on hemodialysis is increasing rapidly. As a result, more patients with ESRD need surgery. These patients have a significantly higher risk of postoperative death than those with normal kidney function. Therefore, this study analyzed the causes of postoperative mortality in ESRD patients undergoing surgery under general anesthesia and the risk factors for postoperative mortality. METHODS: This retrospective analysis examined the mortality of ESRD patients, 20 to 80 years old, undergoing surgery under general anesthesia. We excluded patients who underwent cardiac, cancer, or emergency surgery or organ transplantation from the analysis. The primary outcome was the cause of postoperative 30-day mortality in ESRD patients. We also assessed the mortality rate and risk factors. RESULTS: There were 2,459 eligible ESRD patients. When patients underwent multiple surgeries during the study period, only the last surgery was considered. In total, 167 patients died during the study period, including 65 within 30 days postoperatively. The cause of death was sepsis in 22 cases (33.8%) and a major cardiac event in 16 (24.6%). Atrial fibrillation, current angina, previous myocardial infarction, asthma, lower hemoglobin and albumin levels, and a larger intraoperative colloid volume were likely to increase mortality. CONCLUSIONS: Our study suggests that immunological issues have a significant role in the death of ESRD patients after general anesthesia.