Optimization of a Two-Species Microbial Consortium for Improved Mcl-PHA Production From Glucose–Xylose Mixtures

Polyhydroxyalkanoates (PHAs) have attracted much attention as a good substitute for petroleum-based plastics, especially mcl-PHA due to their superior physical and mechanical properties with broader applications. Artificial microbial consortia can solve the problems of low metabolic capacity of single engineered strains and low conversion efficiency of natural consortia while expanding the scope of substrate utilization. Therefore, the use of artificial microbial consortia is considered a promising method for the production of mcl-PHA. In this work, we designed and constructed a microbial consortium composed of engineered Escherichia coli MG1655 and Pseudomonas putida KT2440 based on the “nutrition supply–detoxification” concept, which improved mcl-PHA production from glucose-xylose mixtures. An engineered E. coli that preferentially uses xylose was engineered with an enhanced ability to secrete acetic acid and free fatty acids (FFAs), producing 6.44 g/L acetic acid and 2.51 g/L FFAs with 20 g/L xylose as substrate. The mcl-PHA producing strain of P. putida in the microbial consortium has been engineered to enhance its ability to convert acetic acid and FFAs into mcl-PHA, producing 0.75 g/L mcl-PHA with mixed substrates consisting of glucose, acetic acid, and octanoate, while also reducing the growth inhibition of E. coli by acetic acid. The further developed artificial microbial consortium finally produced 1.32 g/L of mcl-PHA from 20 g/L of a glucose–xylose mixture (1:1) after substrate competition control and process optimization. The substrate utilization and product synthesis functions were successfully divided into the two strains in the constructed artificial microbial consortium, and a mutually beneficial symbiosis of “nutrition supply–detoxification” with a relatively high mcl-PHA titer was achieved, enabling the efficient accumulation of mcl-PHA. The consortium developed in this study is a potential platform for mcl-PHA production from lignocellulosic biomass.

A Novel Neutral and Mesophilic β-Glucosidase from Coral Microorganisms for Efficient Preparation of Gentiooligosaccharides

β-glucosidases can produce gentiooligosaccharides that are lucrative and promising for the prebiotic and alternative food industries. However, the commercial production of gentiooligosaccharides using β-glucosidase is challenging, as this process is limited by the need for high thermal energy and increasing demand for the enzyme. Here, a putative β-glucosidase gene, selected from the coral microbial metagenome, was expressed in Escherichia coli. Reverse hydrolysis of glucose by Blg163 at pH 7.0 and 40 °C achieved a gentiooligosaccharide yield of 43.02 ± 3.20 g·L−1 at a conversion rate of 5.38 ± 0.40%. Transglycosylation of mixed substrates, glucose and cellobiose, by Blg163 consumed 21.6 U/0.5 g glucose/g cellobiose, achieving a gentiooligosaccharide yield of 70.34 ± 2.20 g·L−1 at a conversion rate of 15.63%, which is close to the highest yield reported in previous findings. Blg163-mediated synthesis of gentiooligosaccharides is the mildest reaction and the lowest β-glucosidase consumption reported to date.

Changes in Browning Degree and Reducibility of Polyphenols during Autoxidation and Enzymatic Oxidation

In the present study, the browning degree and reducing power of browning products of catechin (CT), epicatechin (EC), caffeic acid (CA), and chlorogenic acid (CGA) in autoxidation and enzymatic oxidation were investigated. Influencing factors were considered, such as pH, substrate species and composition, and eugenol. Results show that polyphenols’ autoxidation was intensified in an alkaline environment, but the reducing power was not improved. Products of enzymatic oxidation at a neutral pH have higher reducing power than autoxidation. In enzymatic oxidation, the browning degree of mixed substrates was higher than that of a single polyphenol. The reducing power of flavonoid mixed solution (CT and EC) was higher than those of phenolic acids’ (CA and CGA) in autoxidation and enzymatic oxidation. Eugenol activity studies have shown that eugenol could increase autoxidation browning but inhibit enzymatic browning. Activity test and molecular docking results show that eugenol could inhibit tyrosinase.

Influence of Kappaphycus Alvarezii and Gracilaria Salicornia Supplementation on in Vitro Fermentation Pattern, Total Gas and Methane Production of Mixed Substrates

This experiment was conducted to study the effect of supplementation of Kappaphycus alvarezii (KA) and Gracilaria salicornia (GS) in vitro fermentation pattern, total gas and methane production of mixed substrates. Basal substrate comprising of concentrates and wheat straw (50:50) was supplemented with either 0% (control), 1 (KA1), 2 (KA2), 4 (KA4), 6 (KA6), and 8 % (KA8) of Kappaphycus; and, 1 (GS1), 2 (GS2), 4 (GS4), 6 (GS6), and 8 (GS8 ) of Gracilaria, respectively. Asymptote, rate constant of gas production and t-half, concentration of total volatile fatty acids (TVFA), and in vitro dry matter digestibility (IVDMD) was not affected up to 2% level KA supplementation, beyond which asymptote, and rate constant of gas production, TVFA, and IVDMD decreased and t-half increased (P<0.001). Asymptote, rate constant of gas production, TVFA and IVDMD was not affected at 1% level of inclusion, beyond which a steady decline in these parameters was observed (P<0.001). Methane production (ml/g DM) was higher (P<0.001) in CON, followed by KA1 and KA2, and lower values were observed in by KA4, KA6 and KA8. Methane production (ml/kg DM) declined (P<0.001) steadily with increased level of GS in the substrates. From the results it was concluded that inclusion of Kappaphycus alvarezii and Gracilaria salicornia at 2 and 1%, respectively in the fermentation substrate can reduce in vitro methane production without any adverse impact on total gas production and in vitro dry matter digestibility.

Seed Germination and Seedling Growth of Four Bedding Plants in Substrate Containing Coal Bottom Ash Mixed with Coir Dust

Coal bottom ash (BA) is a by-product of coal-fired power generation and can be utilized as a growing substrate for ornamental plants. The physical and hydraulic properties of BA-mixed substrates (coir dust:BA, 10:0, 9:1, 8:2, 7:3, and 6:4, v/v) and commercial germinating media (BM2; Berger Peatmoss) were investigated, and the effects of the substrate mixtures on seed germination, seedling growth, and heavy metal concentrations (Cd and Pb) were evaluated for four common bedding plants (periwinkle (Catharanthus roseus), globe amaranth (Gomphrena globose), impatiens (Impatiens walleriana), and petunia (Petunia multiflora)). As the BA:coir dust increased, the air space rate in the substrate increased from 25.5 to 28.0%, providing the substrate with sufficient porosity. However, the container capacity and amount of easily available water decreased from 63.1 to 53.7% as BA proportions increased. In the final germination percentage and days to germination of the four bedding plants, no significant differences were detected among the substrate mixtures. Although the impatiens and petunias displayed poor growth (46–55% and 42–56% of dry weight, respectively) in the BA-mixed substrates compared to the BM2, no apparent differences in the seedling growth of periwinkles and globe amaranths were found between 7:3 (coir dust:BA) substrate and BM2. These results indicated that the BA-mixed substrates had the potential to replace the commercial germinating media. The plants grown in the BA-mixed substrates contained Cd, but it was unlikely to be derived from the BA.

Pruning Wastes From Fruit Trees as a Substrate for Pleurotus ostreatus

Plant material obtained by pruning and production of deciduous fruit trees was evaluated as substrates for the production of the oyster mushroom, Pleurotus ostreatus . Lignified branches and stems from peach, apple, and pear trees were processed using a ripping machine to reduce the size of chips and to optimize disinfection. A completely randomized experimental design was proposed with six treatments (novel substrates) and one absolute control (100% hay substrate). Morphological variables such as thickness and diameter of the pileus, stipe length were assessed, as well as production variables (sprouting, fresh weight, and biological efficiency) and bromatological analysis (ash, ethereal extract, crude fiber, and crude protein). Apart from the 100%-hay substrate, biological efficiency ranged between 27% (100% apple tree as the substrate) and 140% (50% hay + 50% peach tree as the substrate). According to morphological analysis, the highest diameters were recorded from mixed substrates (50% hay + 50% wood), and a highly significant positive correlation was found between diameter and stipe length. Morphological parameters were not significantly correlated with biological efficiency. Analysis of biological efficiency confirmed that mixed substrates clustered together with 100%-wood substrates. Bromatological analysis showed that the mixed substrate (50% hay + 50% pear tree) had the highest protein content among the novel tested substrates. Bromatological parameters were not significantly correlated with biological efficiency. In conclusion, pruning residues from fruit trees can be valuable by using them as substrates for the cultivation of P. ostreatus . Production is quantitatively competitive with that using hay, on the condition that wood is mixed with hay.

Photoelectrocatalytic generation of miscellaneous oxygen-based radicals towards cooperative degradation of multiple organic pollutants in water

In the present photoelectrochemical (PEC) system utilizing MoS2 nanoflakes as a wide spectrum absorptive photoanode, simultaneous PEC degradation of different organic pollutants was achieved by employing in situ generated oxysulfur radicals, superoxide and hydroxyl radicals as strong oxidants. In order to better understand the cooperative PEC degradation of representative organic pollutants including rhodamine B dye (RhB), chlorpyrifos (CPF) and ciprofloxacin (CIP), the influences by bias potential, solution pH, radical scavenger, dissolved oxygen concentration and electrolyte concentration have been investigated. The selective PEC degradation efficiency follows the order of CPF &gt; RhB &gt; CIP in mixed substrates condition. In addition, the degradation rate for the single substrate degradation was about two times higher compared to that in mixed substrates degradation. The experimental results verified that reactive oxidation species (ROS) including oxysulfur radicals, superoxide and hydroxyl radicals can be efficiently produced on both anode and cathode under visible light irradiation, and they work together for simultaneous degradation of different pollutants, but the contribution of each ROS for pollutant degradation is substrate dependent. These results indicate that cooperative oxidation of multiple pollutants by miscellaneous oxygen-based radicals should be further considered as a promising advanced oxidation technique.

Physicochemical properties and storage stability of mushrooms (Pleurotus ostreatus) cultivated on single (sawdust) and mixed substrates (sawdust and oil palm fibre)

Oyster mushroom nutrientshave been rated side by side with proteinsin meat and eggs. Oyster mushroomsarehigh in vitamins and essential amino acids, but theircultivation is poor. Oil palm fibre is being used in making material strength in mechanical engineering with little or no use in the cultivation of food products. This study determined the physicochemical properties and storage stability of mushroomscultivated on single and mixed substrates (sawdust and oil palm fibre). Oil palm fibremixed with sawdust at different ratios (95:5, 90:10 and 85:15) was used to grow oyster mushroomsin other to turn waste to wealth. The oyster mushroomscultivated on both single and mixed substratesweresubjected to proximate composition analysis (22.99, 4.54, 6.93,and 6.98%, for crude protein, fat, fibre, and ash),mineral content (5.92 mg/100g for sodium and 25.76 mg/100g for potassium), amino acid profile (155.85 mg/g for a total essential amino acid), fatty acid profile (43.82% for linoleic acid), anti-nutritional factor, and storage stability for three months. The mushroomscultivated on the mixed substrate (oil palm fibre + sawdust) havea higher proximate composition, mineral content, amino acid profile,and fatty acid profiles than mushroomscultivated on a single substrate (sawdust). Although the peroxide value of the oyster mushroom samples from the mixed substrates increased with storage time, the peroxide value was lower than 10 meq/kg of fat throughout the storage period,which means the samples could still be considered stable during storage. Cultivation of oyster mushroomson mixed substrates of oil palm fibreand sawdust should be encouraged for highly nutritious oyster mushroom production. Oil palm fibre can also serve as a raw material in mushroom cultivation.