Bacterial community structure in full-scale mesophilic anaerobic digesters treating cattle or swine manure is determined by substrate type and free ammonia

Received: 05-Oct-2022, Manuscript No. PULJEM-23-6088; Editor assigned: 07-Oct-2022, Pre QC No. PULJEM-23-6088 (PQ); Accepted Date: Oct 18, 2022; Reviewed: 12-Oct-2022 QC No. PULJEM-23-6088 (Q); Revised: 14-Oct-2022, Manuscript No. PULJEM-23-6088 (R); Published: 19-Oct-2022, DOI: 10.37532/puljem.22.4 (5).1-2

Citation: Aaron J. Bacterial community structure in full-scale mesophilic anaerobic digesters treating cattle or swine manure is determined by substrate type and free ammonia. J. Environ. Microbiol. 2022;4(5):1- 2

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Abstract

Anaerobic Digestion (AD), which is mediated by microorganisms, is a highly effective biological method for the treatment of organic waste and the production of biogas. The primary determinants of bacterial community structure and the potential core and distinctive bacterial populations in manure anaerobic digesters are still not fully understood. Using high-throughput 16S rRNA amplicon sequencing, we examined the changes in bacterial community compositions in 20 full-scale anaerobic digesters processing bovine or swine dung for this study. Free Ammonia (FA) and substrate type appeared to be important factors in shaping the organisation of the bacterial population, according to clustering and correlation analysis. The most significant operational indicators that could be used to relate the bacterial populations in the digesters for swine and cow dung, respectively, were the COD: NH+ 4N (C: N) ratio of the substrate and FA. Firmicutes, followed by Bacteroidetes, Proteobacteria, and Chloroflexi, dominated the bacterial populations in all of the digesters. Firmicutes with higher FA content were chosen, indicating that these organisms possibly have more significant roles under high FA concentration. When FA level is high, syntrophic metabolism by Proteobacteria, Chloroflexi, Synergistetes, and Planctomycetes is likely suppressed. Despite varying manure substrates, operational circumstances, and digester locations, core bacterial populations were found. The phylum Firmicutes, where Clostridium predominated heavily, best described the core communities. Communities that are plentiful and specific to the substrate may indicate operational circumstances and manure substrate characteristics. Our present understanding of the bacterial assembly in large-scale manure anaerobic digesters is expanded by these findings.

Key Words

Anaerobic; Bacteroidetes; Correlation; Firmicutes; Proteobacteria; Chloroflexi

Introduction

An effective method for handling different types of organic waste and producing biogas is Anaerobic Digestion (AD). Substrate hydrolysis, fermentation, acetogenesis, and methanogenesis are the four sequential processes in the biological process, which call for the cooperation of bacteria and archaea. Archaea, particularly methanogens, are important participants in methanogenesis and hence receive a lot of attention. However, because of the nature of complex and resistant substrates, the hydrolysis stage is frequently the bottleneck of the AD process in anaerobic digesters processing insoluble organic waste, such as animal dung. In order to establish stable performance during the AD processes, bacteria also manage the crucial syntrophic metabolism linked with methanogenesis.

Microbial community structures are influenced by a number of variables, including digester design, substrate, and operational circumstances. The composition of the microbial population and the effectiveness of fermentation are both known to be significantly influenced by the substrate. The bacterial and archaeal communities' cluster analysis reveals that reactors that process related substrates tend to cluster together. Based on a meta-analysis of 16S rRNA gene sequences recovered from 79 digesters treating various substrates, it is hypothesised that substrate type determines the observed variances in phylogenetic structure. However, microbial communities in anaerobic manure digesters can show significant variances even when a common core substrate is being digested.

The composition of the bacterial community may be affected by operational factors such as temperature and ammonia level. In labscale thermophilic digesters, it has been claimed that bacterial communities grouped according to factors rather than the input materials. That is presumably due to the fact that hot weather has significantly stronger effects on communities than other operational circumstances. Animal dung is frequently used as a substrate in anaerobic digesters and, because it contains so much protein, it frequently has significant levels of Free Ammonia (FA). FA may passively permeate into cells, resulting in proton imbalance and potassium shortage, which inhibits or perhaps has a toxic effect on bacterial communities. FA prevents pH-sensitive organisms as well. Under conditions of high ammonia content, Syntrophic Acetate Oxidisation (SAO) carried out by SAO bacteria is seen to become significant.

Therefore, prokaryotic communities in anaerobic digesters that handle animal dung may be structured by the selectivity of ammonia to various microbial populations.

Core communities expressed by Operational Taxonomic Units (OTUs) are frequently observed in various anaerobic digesters with comparatively high abundances. Additionally, it was shown that microbial populations capable of substrate hydrolysis, fermentation, and syntrophic metabolism contain core communities of anaerobic digesters. They could change depending on the substrate. Therefore, it may be helpful to identify putatively relevant organisms for microbial control in AD by elucidating the core and distinctive communities found in various full-scale anaerobic digesters. Previously, the clone library method was used to identify core and unique OTUs in full-scale anaerobic digesters. core shared by three anaerobic digesters.

Due to the small number of samples of full-scale biogas reactors, information is currently scarce. Using more independently run full-scale anaerobic digesters and high-throughput techniques will help identify the core and distinct OTUs. By the end of the year, China had 3717 large-scale (digester volume >500 m3) and 18,853 medium-scale (digester volume 50 m3–500 m3) biogas plants operating. Two of these substrates that are most used are swine and cow dung. There are numerous full-scale anaerobic digesters that handle animal waste, but very few research has been done to determine the potential core and distinctive bacterial populations, as well as the causes causing the assembly of the bacterial communities.