The Impact of Exogenous Aerobic Bacteria on Sustainable Methane Production Associated with Municipal Solid Waste Biodegradation: Revealed by High-Throughput Sequencing

Biostimulation accelerates landfill stabilization and resource utilization efficiency, providing feasible technical support for the overall lifecycle management of landfills

Although sanitary landfill is one of the principal municipal solid waste (MSW) treatment and disposal methods, its limitations, such as insufficient use of resources, long stability time, and high risk of environmental pollution, must be urgently resolved. The effect of multifunctional microbial community (MMC) inoculation on MSW landfill process was investigated using simulated anaerobic bioreactor landfill (ABL), and composition and microbial community structure of waste, leachate water quality, and gas production were monitored. MMC inoculation significantly accelerated lignocellulose degradation, and the (Hemicellulose content + Cellulose content)/Lignin content ((C + H)/L) of MMC inoculation treatment was 0.89 ± 0.04 on day 44, which was significantly lower than that of the control group (1.14 ± 0.02). At the end of the landfill process, the reductive organic matter, ammonia nitrogen, and volatile fatty acids in the leachate of the MMC group decreased to 9400.00 ± 288.68, 332.78 ± 5.77, and 79.33 ± 6.44 mg L-1, respectively, significantly lower than those of the control group (24,167.00 ± 208.17, 551.14 ± 5.60, and 156.33 ± 8.22 mg L-1). Meanwhile, MMC inoculation increased the methane production to 118.12 ± 5.42 L kg-1 of dry matter, significantly higher than the output of the control group (60.60 ± 2.24 L kg-1). MMC inoculation optimized the microbial community structure in ABL and increased lignocellulose-degrading microorganisms (Brevundimonas, Cellvibrio, Leifsonia, and Devosia) and methanogen (Methanosaeta and Methanoculleus) abundance in the middle stage of landfill. Moreover, MMC introduction improved the abundance of carbon metabolism enzymes and increased saprophytic fungal abundance by 30.09% in the middle stage of landfill. Overall, these findings may help in developing an effective method to increase the lifespan of landfills and enhance their post-closure management.

Bacterial Community Structure and Predicted Metabolic Function of Landfilled Municipal Solid Waste in China

The biodegradation behavior of municipal solid waste (MSW) depends on the diversity and metabolic function of bacterial communities, which are affected by environmental factors. However, the diversity of the bacterial communities and metabolic functions in MSW, as well as their influencing factors, remain unclear. In deep-aged MSW, the abovementioned deficiencies are more significant, and will effectively hamper landfill disposal. In this study, high-throughput sequencing was performed to examine the bacterial community structure and metabolic function from depths of 10 m to 40 m, of two large MSW landfills on the southeast coast of China. Thermotogota (1.6–32.0%), Firmicutes (44.2–77.1%), and Bacteroidota (4.0–34.3%) were the three dominant phyla among the 39 bacterial phyla identified in aged MSW samples. Bacterial genera associated with the degradation of many macromolecules, e.g., Defluviitoga, Hydrogenispora, and Lentimicrobium were abundantly detected in MSW samples, even in aged MSW. Redundancy analysis (RDA) showed that bacterial diversity in the landfills was most strongly correlated with electrical conductivity, age, and moisture content of the MSW. Tax4fun2 analysis predicted that there were abundant metabolism functions in aged MSW, especially functional enzymes (e.g., glycine dehydrogenase and cellulase) related to amino acids and cellulose degradation. This study increases our understanding of the bacterial diversity and functional characteristics in landfilled MSW.

Effect of the C/N Ratio on Biodegradation of Ciprofloxacin and Denitrification from Low C/N Wastewater as Assessed by a Novel 3D-BER System

Emerging pollutants in the form of pharmaceuticals have drawn international attention during the past few decades. Ciprofloxacin (CIP) is a common drug widely found in effluents from hospitals, industrial and different wastewater treatment plants, as well as rivers. In this work, the lab-scale 3D-BER system was established, and more than 90% of the antibiotic CIP was removed from Low C/N wastewater. The best results were obtained with the current intensity being taken into account, and a different C/N ratio significantly improved the removal of CIP and nitrates when the ideal conditions were C/N = 1.5–3.5, pH = 7.0–7.5 and I = 60 mA. The highest removal efficiency occurred when CIP = 94.2%, NO3−-N = 95.5% and total nitrogen (TN) = 84.3%, respectively. In this novel system, the autotrophic-heterotrophic denitrifying bacteria played a vital role in the removal of CIP and an enhanced denitrification process. Thus, autotrophic denitrifying bacteria uses CO2 and H2 as carbon sources to reduce nitrates to N2. This system has the assortment and prosperous community revealed at the current intensity of 60 mA, and the analysis of bacterial community structure in effluent samples fluctuates under different conditions of C/N ratios. Based on the results of LC-MS/MS analysis, the intermediate products were proposed after efficient biodegradation of CIP. The microbial community on biodegrading was mostly found at phylum, and the class level was dominantly responsible for the NO3−-N and biodegradation of CIP. This work can provide some new insights towards the biodegradation of CIP and the efficient removal of nitrates from low C/N wastewater treatment through the novel 3D-BER system.

Mining the Microbiome of Key Species from African Savanna Woodlands: Potential for Soil Health Improvement and Plant Growth Promotion

(1) Aims: Assessing bacterial diversity and plant-growth-promoting functions in the rhizosphere of the native African trees Colophospermum mopane and Combretum apiculatum in three landscapes of the Limpopo National Park (Mozambique), subjected to two fire regimes. (2) Methods: Bacterial communities were identified through Illumina Miseq sequencing of the 16S rRNA gene amplicons, followed by culture dependent methods to isolate plant growth-promoting bacteria (PGPB). Plant growth-promoting traits of the cultivable bacterial fraction were further analyzed. To screen for the presence of nitrogen-fixing bacteria, the promiscuous tropical legume Vigna unguiculata was used as a trap host. The taxonomy of all purified isolates was genetically verified by 16S rRNA gene Sanger sequencing. (3) Results: Bacterial community results indicated that fire did not drive major changes in bacterial abundance. However, culture-dependent methods allowed the differentiation of bacterial communities between the sampled sites, which were particularly enriched in Proteobacteria with a wide range of plant-beneficial traits, such as plant protection, plant nutrition, and plant growth. Bradyrhizobium was the most frequent symbiotic bacteria trapped in cowpea nodules coexisting with other endophytic bacteria. (4) Conclusion: Although the global analysis did not show significant differences between landscapes or sites with different fire regimes, probably due to the fast recovery of bacterial communities, the isolation of PGPB suggests that the rhizosphere bacteria are driven by the plant species, soil type, and fire regime, and are potentially associated with a wide range of agricultural, environmental, and industrial applications. Thus, the rhizosphere of African savannah ecosystems seems to be an untapped source of bacterial species and strains that should be further exploited for bio-based solutions.

Diversity of Trichoderma spp. in Marine Environments and Their Biological Potential for Sustainable Industrial Applications

Microorganisms are regarded as a sustainable source of biologically active molecules. Among them, Trichoderma spp. have been an attractive source of biological compounds. However, the study of marine-derived Trichoderma has developed slowly because of the difficulty in isolating the fungi. In our study, 30 strains of marine-derived Trichoderma were identified through the translation elongation factor 1-alpha (EF1α) sequences, and their biological activities, such as antioxidant activity by ABTS and DPPH assays, antifungal activity against Asteromyces cruciatus and Lindra thalassiae, and tyrosinase inhibition activity, were investigated. As a result, the 30 marine Trichoderma species were classified into 21 taxa, including three new species candidates. Three strains of T. asperellum showed the highest ABTS radical scavenging activity and antifungal activity. T. bissettii SFC20170821-M05 and T. guizhouense SFC20180619-M23 showed notable DPPH radical scavenging activity and tyrosinase inhibition activity, respectively. This study showed the potential of marine-derived Trichoderma as a source of bioactive compounds.