Background Anaerobic digestion is a microbial driven process, which results in biogas production. Although important, the relative abundance of microbial communities can be affected by disturbances such as feeding rates. In this study, the effects of irregular organic loading rates on anaerobic digestion of water hyacinth (mono‐ and co‐digestion) as well as on bacterial and archaeal communities were investigated. The process was conducted at different feeding stages during which the process stability, biogas production, composition and microbial community structure were monitored. Results Bacterial communities were more influenced by irregular organic loading rates in comparison with archaeal communities. Although microbial community shifts were observed in both mono‐ and co‐digestion, the shift was more prevalent in co‐digestion. Moreover, process stability was evidenced in some stages of mono‐digestion, where the FOS/TAC ratio was within the optimal range. However, for co‐digestion, the low FOS/TAC ratio showed process instability. Conclusion Overall, irregularity in organic loading rates affected the microbial community composition as well as their CH4 production. © 2018 Society of Chemical Industry

Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation.

An estimated 25 million tons of animal manure is produced globally every year, causing considerable impact to the environment. These impacts can be managed through the use of anaerobic digestion (AD) This process achieves waste degradation through enzymatic activity, the efficiency of the AD process is directly related to microorganisms that produce these enzymes. Biomethane potential (BMP) assays remain the standard theoretical framework to pre-determine biogas yield and have been used to determine the feasibility of substrates or their combination for biogas production. However, an integrated approach that combines substrate choice and co-digestion would provide an improvement to the current predictive models. PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) addresses the limitations of assays in this regard. In this paper, the biochemical functions of horse, cow, and pig manures are predicted. A total of 135 predicted KEGG Orthologies (KOs) showed amino acids, carbohydrate, energy, lipid, and xenobiotic metabolisms in all the samples. Linear discriminant analysis (LDA) combined with the effect size measurements (LEfSe), showed that fructose, mannose, amino acid and nucleotide sugar, phosphotransferase (PST) as well as starch and sucrose metabolisms were significantly higher in horse manure samples. 36 of the KOs were related to the acidogenesis and/or acetogenesis AD stages. Extended bar plots showed that 11 significant predictions were observed for horse-cow, while 5 were predicted for horse-pig and for cow-pig manures. Based on these predictions, the AD process can be enhanced through co-digestion strategies that takes into account the predicted metabolic contributions of the manure samples. The results supported the BMP calculations for the samples in this study. Biogas yields can be improved if this combined approach is employed in routine analysis before co-digesting different substrates.

BACKGROUND Water hyacinth (Eichhornia crassipes) is a fast growing water weed that threatens the aquatic ecosystem and human activities, hence control of the plant is essential. One such control approach is to harvest and utilize hyacinth as a substrate for anaerobic digestion (AD). Various factors influence AD performance, including substrate pre‐treatment and microbial community composition, amongst others. This study was aimed at establishing the link between method of substrate pre‐treatment, microbial diversity, inoculum addition and biogas yield during AD of hyacinth. RESULTS The addition of an inoculum resulted in microbial community stability and early biomethane production of up to 0.4 L irrespective of pre‐treatment method. However, cultures that lacked inoculum showed distinct microbial community structure variation in response to pre‐treatment method, and minimal early biomethane production (up to 0.1 L). Biogas produced by cultures lacking inoculum was initially mostly composed of carbon dioxide (up to 100% of total biogas), but as digestion proceeded, an increase in biomethane production was observed (up to 60% of total biogas), which correlated with the shift in microbial community structure and increased microbial diversity. This indicates the presence of biogas‐producing microorganisms associated with the collected hyacinth. Canonical correspondence analysis proved that dynamic changes in microbial community structure and biogas yield were strongly correlative. CONCLUSION This study proves that hyacinth pre‐treatment influences microbial community structure and concomitant biogas yield in the absence of an inoculum. The addition of an inoculum aids in stability of microbial community structure and biogas yield irrespective of method of hyacinth pre‐treatment. © 2019 Society of Chemical Industry

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The hostile environment of mine tailings contains unique microbial life capable of bioleaching. The metagenomic analysis of such an environment provides an in-depth understanding of the microbial life and its potential, especially in biomining operations. However, DNA recovery from samples collected in those environments is challenging due to the presence of metal ions that interfere with the DNA analysis. A varied concentration of EDTA (4–13 µg/µL) to chelate the metal ions of enriched tailing samples prior to DNA extraction was performed. The results show that 9 µg/µL of EDTA was effective in most samples. However, the increasing concentration of EDTA negatively affected the DNA recovery. The sequencing of the successfully extracted DNA revealed a diverse range of fungal genera, some of which have not been previously reported in tailing or bioleaching applications. The dominant genera include Fodinomyces, Penicillium, Recurvomuces, Trichoderma, and Xenoacremonium; their traits were determined using the FungalTraits database. This study demonstrates the need to include a preliminary metal-chelating step using EDTA before DNA extractions for samples collected from metal-rich environments. It further showed the need for optimization but provided a benchmark range, particularly for tailings. However, we caution that a further EDTA removal step from the extracted DNA should be included to avoid its interferences in downstream applications.

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