Biochar reduces bioavailability of phosphorus during swine manure composting: Roles of phoD-harboring bacterial community.

The bioavailability of phosphorus is a vital index for evaluating the quality of compost products. This study examined the effects of adding wheat straw biochar (WSB) and bamboo charcoal (BC) on the transformation of various phosphorus fractions during composting, as well as analyzing the roles of the phoD-harboring bacterial community in the transformation of phosphorus fractions. Adding WSB and BC reduced the available phosphorus content in the compost products by 35.2 % and 38.5 %, respectively. Redundancy analysis showed that the alkaline phosphatase content and pH were the most important factors that affected the transformation of phosphorus fractions. The addition of biochar resulted in changes in the composition and structures of the phoD-harboring bacteria communities during composting. In addition, the key bacterial genera that secreted alkaline phosphatase and decomposed different forms of phosphorus under WSB and BC were different compared with those under control. Network and correlation analysis demonstrated that the activities of phoD-harboring bacteria could have been enhanced by biochar to accelerate the consumption of available phosphorus, and the activities of key phosphorus-solubilizing bacteria (Lysobacter, Methylobacterium, and Saccharothrix) might be inhibited when the pH increased, thereby increasing the insoluble phosphorus content.

Mechanisms of enhanced hydrogen production from sewage sludge by ferrous ion: Insights into functional genes and metabolic pathways.

Hydrogen production from sewage sludge was studied in the presence of Fe2+. The results showed that the highest cumulative hydrogen production of 26 mL/100 mL was achieved with 600 mg/L Fe2+ supplementation, which was 2 times of the control test. In depth analysis of organics in liquid phase revealed that Fe2+ addition promoted sludge disintegration and protein degradation during fermentation process. Functions prediction by PICRUSt analysis indicated the effect of Fe2+ on microbial metabolism and functional genes expression. The results showed that the expression of hydrogen-producing functions, like ferredoxin hydrogenase and formate dehydrogenase was activated by Fe2+ supplementation, while the hydrogen-consuming metabolism, like methane metabolism and homoacetogenic metabolism was inhibited. Furthermore, Fe2+ addition could stimulate organics utilization. This study explored the effect of Fe2+ on functional genes abundance, revealing the mechanisms of enhanced hydrogen production by Fe2+ from the perspective of microbial metabolism.

Mechanisms of enhanced biohydrogen production from macroalgae by ferrous ion: Insights into correlations of microbes and metabolites.

This study explored the mechanisms of the enhanced hydrogen production from macroalgae by Fe2+ supplementation. Highest hydrogen yield of 19.47 mL/g VSadded was achieved at Fe2+ supplementation of 400 mg/L, which was 6.25 times of the control test. In depth analysis of substrate degradation, microbial distribution and metabolites formation was conducted. The results showed that Fe2+-supplemented group was dominated by Clostridium butyricum (67.2%) and Ruminococcus gnavus (24.2%), which stimulated hydrogen generation and volatile organic acids accumulation. In contrast, Fe2+-deficient group had a microbial community dominated by Exiguobacterium sp. (29.0%), Acinetobacter lwoffii (24.5%) and Clostridium stricto 13 (23.4%), which induced higher efficiency of both biomass hydrolysis and mineralization. Microbes from a single system were mutually cooperative, while microbes from Fe2+-deficient and those from Fe2+-supplemented systems were mutually exclusive. This study suggested that Fe2+ is critical in macroalgae fermentation system to affect the microbial community structure and subsequently switch the metabolic pathways.

Enhanced biohydrogen production from macroalgae by zero-valent iron nanoparticles: Insights into microbial and metabolites distribution.

In this work, effect of Fe0 nanoparticles (Fe0 NPs) on macroalgae fermentation was explored. Hydrogen production was significantly enhanced by 6.5 times comparing with control test, achieving 20.25 mL H2/g VSadded with addition of 200 mg/L Fe0 NPs. In-depth analysis of substrate conversion showed that both hydrogen generation and acids accumulation were promoted with Fe0 NPs supplementation. Microbial analysis demonstrated that both hydrogen-producing strains belonging to genus Clostridium and Terrisporobacter sp. favorable for acids formation were enriched with Fe0 NPs supplementation, while species Acinetobacter lwoffii beneficial to organics mineralization was eliminated. Complex substrate compositions resulted in more prevalent cooperative relationships among species in the system. This study suggested that Fe0 NPs plays a crucial role in macroalgae fermentation by affecting the microbial distribution, subsequently influencing the products distribution and energy conversion.

Behavior of antibiotic resistance genes during co-composting of swine manure with Chinese medicinal herbal residues.

Swine manure is considered to be a reservoir for antibiotic resistance genes (ARGs) but little is known about the variations in ARGs during the co-composting of swine manure with Chinese medicinal herbal residues (CMHRs). Thus, this study explored the effects of CMHRs on the variations in ARGs during co-composting with swine manure. The results showed that CMHRs could reduce effectively most of the targeted ARGs (0.18-2.82logs) and mobile genetic elements (MGEs) (0.47-3.34logs). The correlations indicated that CMHRs might decrease the spread of ARGs via horizontal gene transfer. Redundancy analysis showed that the bacterial communities had more important effects on the variations in ARGs compared with environmental factors and MGEs. The results of this study demonstrate that CMHRs can decrease the abundances of ARGs and MGEs, as well as reducing the risk of ARGs spreading during the application of compost products to farmland.