Structure-function elucidation of a microbial consortium in degrading rice straw and producing acetic and butyric acids via metagenome combining 16S rDNA sequencing

Synergistic analysis of lignin degrading bacterial consortium and its application in rice straw fiber film

Fiber film have received widespread attention due to its green friendliness. We can use microorganisms to degrade lignin in straw to obtain cellulose and make fiber films. Herein, a group of high-temperature (50 °C) lignin degrading bacterial consortium (LDH) was enriched and culture conditions for lignin degradation were optimized. Combined with high-throughput sequencing technology, the synergistic effect of LDH-composited bacteria was analyzed. Then LDH was used to treat rice straw for the bio-pulping experiment. The results showed that the lignin of rice straw was degraded 32.4 % by LDH at 50 °C for 10 d, and after the optimization of culture conditions, lignin degradation rate increased by 9.05 % (P < 0.001). The bacteria that compose in LDH can synergistically degrade lignin. Paenibacillus can encode all lignin-degrading enzymes present in the LDH. Preliminary tests of LDH in the pulping industry have been completed. This study is the first to use high temperature lignin degrading bacteria to fabricate fiber film.

Application of pectin hydrolyzing bacteria in tobacco to improve flue-cured tobacco quality

To study the relationship between the diversity of the surface microbial community and tobacco flavor, and to improve tobacco quality using microorganisms. The microbial community composition and diversity of 14 samples of flue-cured tobacco from tobacco-producing areas in Yunnan with varying grades were analyzed by high-throughput sequencing. PICRUSt was used for predicting microbial functions. A strain of Bacillus amyloliquefaciens W6-2 with the ability to degrade pectin was screened from the surface of flued-cured tobacco leaves from Yunnan reroasted tobacco leave. The enzyme preparation was prepared through fermentation and then applied for treating flue-cured tobacco. The improvement effect was evaluated by measuring the content of macromolecule and the changes in volatile components, combined with sensory evaluations. The bacterial communities on the surface of flue-cured tobacco exhibited functional diversity, consisting primarily of Variovorax, Pseudomonas, Sphingomonas, Burkholderia, and Bacillus. These bacterial strains played a role in the aging process of flue-cured tobacco leaves by participating in amino acid metabolism and carbohydrate metabolism. These metabolic activity converted complex macromolecules into smaller molecular compounds, ultimately influence the smoking quality and burning characteristics of flue-cured tobacco. The pectinase preparation produced through fermentation using W6-2 has been found to enhance the aroma and sweetness of flue-cured tobacco, leading to improved aroma, reduced impurities, and enhanced smoothness. Additionally, the levels of pectin, cellulose, and hemicellulose decreased, while the levels of water-soluble sugar and reducing sugar increased, and the contents of esters, ketones, and aldehydes increased, and the contents of benzoic acid decreased. The study revealed the correlation between surface microorganisms and volatile components of Yunnan tobacco leaves, and the enzyme produced by the pectin-degrading bacteria W6-2 effectively improved the quality of flue-cured tobacco.

Enhancing acidification efficiency of vegetable wastes through heat shock pretreatment and initial pH regulation

Anaerobic digestion (AD) technology is a practical approach to alleviate severe environmental issues caused by vegetable wastes (VWs). However, its primary product is methane-rich biogas converted from the precursors (mainly volatile fatty acids, VFAs) after long fermentation periods, making traditional AD projects of low economic profits. Intervening in the methanogenesis stage artificially to produce high value-added VFAs can shorten the reaction time of the AD process and significantly improve profits, posing a promising alternative for treating VWs. Given this, this study applied heat shock (HS) pretreatment to inoculum to prevent methane production during AD and systemically investigated the effects of HS pretreatment and initial pH regulation on VFA production from VWs. The results showed that appropriate HS pretreatment effectively inhibited methane generation but promoted VFA accumulation, and VFA production was further enhanced by adjusting the initial pH to 8.0 and 9.0. The highest total VFA concentration of 14,883 mg/L with a VFA yield of 496.1 mg/gVS, 26.98% higher than that of the untreated group, was achieved at an initial pH 8.0 with HS pretreatment of 80 °C for 1 h. Moreover, pH regulation influenced the metabolic pathway of VFA production from VWs during AD, as butyrate was the dominant product at an initial pH of 6.0, while the increased initial pH improved the acetate proportion.

The performance, mechanism and greenhouse gas emission potential of nitrogen removal technology for low carbon source wastewater

Excessive nitrogen can lead to eutrophication of water bodies. However, the removal of nitrogen from low carbon source wastewater has always been challenging due to the limited availability of carbon sources as electron donors. Biological nitrogen removal technology can be classified into three categories: heterotrophic biological technology (HBT) that utilizes organic matter as electron donors, autotrophic biological technology (ABT) that relies on inorganic electrons as electron donors, and heterotrophic-autotrophic coupling technology (CBT) that combines multiple electron donors. This work reviews the research progress, microbial mechanism, greenhouse gas emission potential, and challenges of the three technologies. In summary, compared to HBT and ABT, CBT shows greater application potential, although pilot-scale implementation is yet to be achieved. The composition of nitrogen removal microorganisms is different, mainly driven by electron donors. ABT and CBT exhibit the lowest potential for greenhouse gas emissions compared to HBT. N2O, CH4, and CO2 emissions can be controlled by optimizing conditions and adding constructed wetlands. Furthermore, these technologies need further improvement to meet increasingly stringent emission standards and address emerging pollutants. Common measures include bioaugmentation in HBT, the development of novel materials to promote mass transfer efficiency of ABT, and the construction of BES-enhanced multi-electron donor systems to achieve pollutant prevention and removal. This work serves as a valuable reference for the development of clean and sustainable low carbon source wastewater treatment technology, as well as for addressing the challenges posed by global warming.

Biophotoelectrochemical process co-driven by dead microalgae and live bacteria

Anaerobic reduction processes in natural waters can be promoted by dead microalgae that have been attributed to nutrient substances provided by the decomposition of dead microalgae for other microorganisms. However, previous reports have not considered that dead microalgae may also serve as photosensitizers to drive microbial reduction processes. Here we demonstrate a photoelectric synergistic linkage between dead microalgae and bacteria capable of extracellular electron transfer (EET). Illumination of dead Raphidocelis subcapitata resulted in two-fold increase in the rate of anaerobic bioreduction by pure Geobacter sulfurreducens, suggesting that photoelectrons generated from the illuminated dead microalgae were transferred to the EET-capable microorganisms. Similar phenomena were observed in NO3- reduction driven by irradiated dead Chlorella vulgaris and living Shewanella oneidensis, and Cr(VI) reduction driven by irradiated dead Raphidocelis subcapitata and living Bacillus subtilis. Enhancement of bioreduction was also seen when the killed microalgae were illuminated in mixed-culture lake water, suggesting that EET-capable bacteria were naturally present and this phenomenon is common in post-bloom systems. The intracellular ferredoxin-NADP+-reductase is inactivated in the dead microalgae, allowing the production and extracellular transfer of photoelectrons. The use of mutant strains confirmed that the electron transport pathway requires multiheme cytochromes. Taken together, these results suggest a heretofore overlooked biophotoelectrochemical process jointly mediated by illumination of dead microalgae and live EET-capable bacteria in natural ecosystems, which may add an important component in the energetics of bioreduction phenomena particularly in microalgae-enriched environments.

Dietary citrus flavonoid extract improves lactational performance through modulating rumen microbiome and metabolites in dairy cows

The effects of dietary supplementation with citrus flavonoid extract (CFE) on milk performance, rumen fermentation, rumen microbiome, rumen metabolome, and serum antioxidant indexes were evaluated. Eight multiparous lactating cows were allocated to a replicated 4 × 4 Latin square with 25-d periods consisting of 20 d of adaptation and 5 d of sampling. Experimental treatments included a control diet (CON) and CON supplemented with 50 g d^-1 (CFE50), 100 g d^-1 (CFE100), and 150 g d^-1 (CFE150). Feeding CFE to dairy cows increased milk production and milk lactose. Milk somatic cell count linearly reduced with increasing CFE amount. Supplementing CFE linearly increased the ruminal concentrations of total volatile fatty acids, acetate, propionate, butyrate, and microbial crude protein. Ruminal lipopolysaccharide linearly decreased with increasing CFE amount. Compared with CON, CFE150 cows exhibited a greater abundance of Firmicutes and a low abundance of Bacteroidetes. Cellulolytic bacteria (genera Ruminococcus, Clostridium, and Butyrivibrio) and carbohydrate metabolism were enriched in the CFE150 cows. For archaea and viruses, major methanogens (genera Methanobacterium and Methanosarcina) and phylum Uroviricota were inhibited in the CFE150 cows. Compared with CON, the ruminal concentrations of tyrosine, proline, pyruvate, glucose, and glucose-6-phosphate were higher in the CFE150 cows. The metabolites of citrus flavonoids, such as hippuric acid, hesperetin, and naringenin, were increased in the CFE150 cows. Supplementing CFE significantly improved the antioxidant capacity of the dairy cows. This study highlighted that dietary supplementation with CFE led to significant changes in the rumen microbial composition and metabolites, and consequently resulted in an improved lactational performance of dairy cows.

Orlistat and ezetimibe could differently alleviate the high-fat diet-induced obesity phenotype by modulating the gut microbiota

This study aimed to evaluate the possible anti-obesity effects of orlistat and ezetimibe and determine the mechanism by which they alter the composition of gut microbiota and short-chain fatty acids (SCFAs) in mice with a high-fat diet (HFD)-induced obesity. Eighty male, specific pathogen-free C57BL/6J mice aged 3 weeks were divided into four groups (n = 20). The NCD group was fed with a normal diet, and the HFD, HFD+ORL, and HFD+EZE groups were fed with HFD for 20 weeks. From the 13th week onward, the HFD+ORL and HFD+EZE groups were administered with orlistat and ezetimibe, respectively. The glucose and lipid metabolism of the tested mice were evaluated by analyzing blood biochemical indicators during the intervention. Furthermore, the changes in the structure of the fecal microbiota and the fecal SCFA content were analyzed by 16S rRNA sequencing and gas chromatography-mass spectrometry, respectively. HFD induced the obesity phenotype in mice. Compared to the HFD group, the body weight, visceral fat-to-body weight ratio, serum total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C), and oral glucose tolerance test (OGTT) of the HFD+ORL group significantly decreased, whereas fecal butyric acid levels significantly increased. Ezetimibe intervention significantly reduced the OGTT, serum TC, and HDL-C levels only. The α-diversity of the gut microbiota significantly decreased after intervention with orlistat and ezetimibe. Orlistat altered the relative abundance of some bacteria in the fecal microbiota. The populations of Firmicutes, Alistipes, and Desulfovibrio decreased, whereas those of Verrucomicrobia and Akkermansia significantly increased. Ezetimibe caused changes only in some low-abundance bacteria, as manifested by a decrease in Proteobacteria and Desulfovibrio, and an increase in Bacteroides. The administration of orlistat and ezetimibe can characteristically influence the body weight and serum lipid metabolism, and glucolipid levels in diet-induced obese mice and is accompanied by significant changes in the gut microbiota and SCFAs. These results suggest that the two drugs might exert their own specific anti-obesity effects by modulating the gut microbiota in a different manner. The enhanced health-promoting effect of orlistat might result from its stronger ability to alter the gut microbiota and SCFAs, at least partly.