Anaerobic bacterial degradation for the effective utilization of biomass

Chitin degradation and electricity generation by Aeromonas hydrophila in microbial fuel cells

Chitin is one of the most abundant biopolymers in nature and the main composition of shrimp and crab shells (usually as food wastes). Thus it is essential to investigate the potential of degrading chitin for energy recovery. This study investigated the anaerobic degradation of chitin by Aeromonas hydrophila, a chitinolytic and popular electroactive bacterium, in both fermentation and microbial fuel cell (MFC) systems. The primary chitin metabolites produced in MFC were succinate, lactate, acetate, formate, and ethanol. The total metabolite concentration from chitin degradation increased seven-fold in MFC compared to the fermentation system, as well as additional electricity generation. Moreover, A. hydrophila degraded GlcNAc (the intermediate of chitin hydrolysis) significantly faster (0.97 and 0.94 mM C/d/mM-GlcNAc) than chitin (0.13 and 0.03 mM C/d/mM-GlcNAc) in MFC and fermentation systems, indicating that extracellular hydrolysis of chitin was the rate-limiting step and this step could be accelerated in MFC. Furthermore, more chemicals produced by the addition of exogenous mediators in MFC. This study proves that the chitin could be degraded effectively by an electroactive bacterium in MFC, and our results suggest that this bioelectrochemical system might be useful for the degradation of recalcitrant biomass to recover energy.

Comparative metagenomics of biogas-producing microbial communities from production-scale biogas plants operating under wet or dry fermentation conditions

BACKGROUND

Decomposition of biomass for biogas production can be practiced under wet and dry fermentation conditions. In contrast to the dry fermentation technology, wet fermentation is characterized by a high liquid content and a relatively low total solid content. In this study, the composition and functional potential of a biogas-producing microbial community in an agricultural biogas reactor operating under wet fermentation conditions was analyzed by a metagenomic approach applying 454-pyrosequencing. The obtained metagenomic dataset and corresponding 16S rRNA gene amplicon sequences were compared to the previously sequenced comparable metagenome from a dry fermentation process, meeting explicitly identical boundary conditions regarding sample and community DNA preparation, sequencing technology, processing of sequence reads and data analyses by bioinformatics tools.

RESULTS

High-throughput metagenome sequencing of community DNA from the wet fermentation process applying the pyrosequencing approach resulted in 1,532,780 reads, with an average read length of 397 bp, accounting for approximately 594 million bases of sequence information in total. Taxonomic comparison of the communities from wet and dry fermentation revealed similar microbial profiles with Bacteria being the predominant superkingdom, while the superkingdom Archaea was less abundant. In both biogas plants, the bacterial phyla Firmicutes, Bacteroidetes, Spirochaetes and Proteobacteria were identified with descending frequencies. Within the archaeal superkingdom, the phylum Euryarchaeota was most abundant with the dominant class Methanomicrobia. Functional profiles of the communities revealed that environmental gene tags representing methanogenesis enzymes were present in both biogas plants in comparable frequencies. 16S rRNA gene amplicon high-throughput sequencing disclosed differences in the sub-communities comprising methanogenic Archaea between both processes. Fragment recruitments of metagenomic reads to the reference genome of the archaeon Methanoculleus bourgensis MS2(T) revealed that dominant methanogens within the dry fermentation process were highly related to the reference.

CONCLUSIONS

Although process parameters, substrates and technology differ between the wet and dry biogas fermentations analyzed in this study, community profiles are very similar at least at higher taxonomic ranks, illustrating that core community taxa perform key functions in biomass decomposition and methane synthesis. Regarding methanogenesis, Archaea highly related to the type strain M. bourgensis MS2(T) dominate the dry fermentation process, suggesting the adaptation of members belonging to this species to specific fermentation process parameters.

Coconut shells as filling material for anaerobic filters

In rural areas of developing countries, there is a lack of sanitation services and the installation of such infrastructure is hampered by the high investment costs for initial implementation and by the limited availability of qualified personnel. An alternative to traditional sanitation services include an anaerobic filter, but the high cost of appropriate filling material can be an obstacle to its wide-spread implementation. To decrease this construction cost, the objective of this work was to study the use of coconut shells as filling material for anaerobic filters. Anaerobic filters were built and filled with the studied material and operated with up flow and hydraulic retention time of 9 hours. The reactors provided a removal of 79 ± 16% in BOD terms, indicating that the coconut shell filling had efficiency consistent with the literature data. In addition, the husks were found to retain their tensile strength following use in the reactors. Coconut husks have more empty bed volume than other low cost materials, such as crushed stone, nearing properties of traditional materials. The results of this study indicate that coconut husks may prove to be a low cost alternative to traditional fillers for anaerobic treatment in rural communities.

Phylogenetic analysis and metabolic potential of microbial communities in an industrial bagasse collection site

Industrial bagasse collection sites at sugar mills are an important resource for biomass-based industries and represent a unique ecological niche in lignocellulose degradation. In this study, microbial community structures at regions with varying microenvironmental conditions contained within a bagasse collection site were explored using tagged 16S rRNA gene pyrosequencing. Overall, remarkable differences in microbial community structures were found in aerobic surface and oxygen-limited interior regions of the pile. A variety of Alphaproteobacteria and Gammaproteobacteria represented the majority of bacteria in the aerobic upper-pile regions with the predominance of acetic acid bacteria towards the outer surface. Diverse Proteobacteria, Bacteroidetes, and Acidobacteria represented the predominant phyla at the exterior soil-contact pile base with an increasing abundance of anaerobic Spirochaetes with the increasing depth, where it shared similar community structures to that in the open-field soil from decomposed bagasse. Using complementary shotgun pyrosequencing, a variety of genes encoding various glycosyl hydrolases targeting cellulose and hemicellulose degradation were identified in the oxygen-limited interior pile base. Most were relevant to orders Clostridiales, Bacteroidales, Sphingobacteriales, and Cytophagales, suggesting their role in lignocellulose degradation in this region, as evidenced by the decrease in cellulose and respective increase in lignin fractions of the biomass. Partial carbon flux in the anoxic region was metabolized through mixed methanogenesis pathways as suggested by the annotated functional genes in methane synthesis. This study gives insights into native microbial community structures and functions in this unique lignocellulose degrading environment and provides the basis for controlling microbial processes important for utilization of bagasse in bio-industries.

Isolation and characterization of a novel pyrene-degrading Bacillus vallismortis strain JY3A

The PAHs-degrading bacterium strain JY3A was newly isolated from the polluted soil in the Jinan Oil Refinery Factory, Shandong Province of China. The isolate was identified as Bacillus vallismortis with respect to its 16S rDNA sequence, DNA-DNA relatedness and fatty acid profiles, as well as various physiological characteristics. The strain was Gram-positive, motile, endospore forming, aerobic, oxidase and catalase-positive. The cells were 0.8-1.0μm wide and 2.0-2.5μm long, single or in pairs and sometimes in chains. Bacillus vallismortis strain JY3A could utilize naphthalene, phenanthrene, anthracene, pyrene, fluorene, benzene, toluene, phenol, methanol, ethanol, Tween 80, cyclohexane or catechol as sole carbon source. The strain alone removed 90.5% of pyrene at an initial concentration of 150ppm in 15days in the presence of 0.5% (w/w) Tween 80. However, in co-culture with Phanerochaete chrysosporium, JY3A reduced the concentration of pyrene by nearly 55.4% after 7days of incubation.

Phylogenetic characterization of a biogas plant microbial community integrating clone library 16S-rDNA sequences and metagenome sequence data obtained by 454-pyrosequencing

The phylogenetic structure of the microbial community residing in a fermentation sample from a production-scale biogas plant fed with maize silage, green rye and liquid manure was analysed by an integrated approach using clone library sequences and metagenome sequence data obtained by 454-pyrosequencing. Sequencing of 109 clones from a bacterial and an archaeal 16S-rDNA amplicon library revealed that the obtained nucleotide sequences are similar but not identical to 16S-rDNA database sequences derived from different anaerobic environments including digestors and bioreactors. Most of the bacterial 16S-rDNA sequences could be assigned to the phylum Firmicutes with the most abundant class Clostridia and to the class Bacteroidetes, whereas most archaeal 16S-rDNA sequences cluster close to the methanogen Methanoculleus bourgensis. Further sequences of the archaeal library most probably represent so far non-characterised species within the genus Methanoculleus. A similar result derived from phylogenetic analysis of mcrA clone sequences. The mcrA gene product encodes the alpha-subunit of methyl-coenzyme-M reductase involved in the final step of methanogenesis. BLASTn analysis applying stringent settings resulted in assignment of 16S-rDNA metagenome sequence reads to 62 16S-rDNA amplicon sequences thus enabling frequency of abundance estimations for 16S-rDNA clone library sequences. Ribosomal Database Project (RDP) Classifier processing of metagenome 16S-rDNA reads revealed abundance of the phyla Firmicutes, Bacteroidetes and Euryarchaeota and the orders Clostridiales, Bacteroidales and Methanomicrobiales. Moreover, a large fraction of 16S-rDNA metagenome reads could not be assigned to lower taxonomic ranks, demonstrating that numerous microorganisms in the analysed fermentation sample of the biogas plant are still unclassified or unknown.

The metagenome of a biogas-producing microbial community of a production-scale biogas plant fermenter analysed by the 454-pyrosequencing technology

Composition and gene content of a biogas-producing microbial community from a production-scale biogas plant fed with renewable primary products was analysed by means of a metagenomic approach applying the ultrafast 454-pyrosequencing technology. Sequencing of isolated total community DNA on a Genome Sequencer FLX System resulted in 616,072 reads with an average read length of 230 bases accounting for 141,664,289 bases sequence information. Assignment of obtained single reads to COG (Clusters of Orthologous Groups of proteins) categories revealed a genetic profile characteristic for an anaerobic microbial consortium conducting fermentative metabolic pathways. Assembly of single reads resulted in the formation of 8752 contigs larger than 500 bases in size. Contigs longer than 10kb mainly encode house-keeping proteins, e.g. DNA polymerase, recombinase, DNA ligase, sigma factor RpoD and genes involved in sugar and amino acid metabolism. A significant portion of contigs was allocated to the genome sequence of the archaeal methanogen Methanoculleus marisnigri JR1. Mapping of single reads to the M. marisnigri JR1 genome revealed that approximately 64% of the reference genome including methanogenesis gene regions are deeply covered. These results suggest that species related to those of the genus Methanoculleus play a dominant role in methanogenesis in the analysed fermentation sample. Moreover, assignment of numerous contig sequences to clostridial genomes including gene regions for cellulolytic functions indicates that clostridia are important for hydrolysis of cellulosic plant biomass in the biogas fermenter under study. Metagenome sequence data from a biogas-producing microbial community residing in a fermenter of a biogas plant provide the basis for a rational approach to improve the biotechnological process of biogas production.