Metagenomics-Guided Mining of Commercially Useful Biocatalysts from Marine Microorganisms

Integrating 16S rRNA amplicon metagenomics and selective culture for developing thermophilic bacterial inoculants to enhance manure composting

Composting is an important method for treating and recycling organic waste, and the use of microbial inoculants can increase the efficiency of composting. Herein, we illustrate an approach that integrate 16S rRNA amplicon metagenomics and selective culture of thermophilic bacteria for the development of inoculants to improve manure composting. The 16S rRNA amplicon sequencing analysis revealed that Firmicutes and Actinobacteria were dominant in the composting mixture, and that different microbial hubs succeeded during the thermophilic stage. All isolated thermophilic bacteria were affiliated with the order Bacillales, such as Geobacillus, Bacillus, and Aeribacillus. These isolated thermophilic bacteria were grouped into 11 phylotypes, which shared ＞99% sequence identity to 0.15% to 5.32% of 16S rRNA reads by the amplicon sequencing. Three of these phylotypes transiently enriched during the thermophilic stage. Six thermophilic bacteria were selected from the three phylotypes to obtain seven microbial inoculants. Five out of seven of the microbial inoculants enhanced the thermophilic stage of composting by 16.9% to 52.2%. Three-dimensional excitation emission matrix analysis further revealed that two inoculants (Thermoactinomyces intermedius and Ureibacillus thermophilus) stimulated humification. Additionally, the 16S rRNA amplicon sequencing analysis revealed that inoculation with thermophilic bacteria enhanced the succession of the microbial community during composting. In conclusion, 16S rRNA amplicon metagenomics is a useful tool for the development of microbial inoculants to enhance manure composting.

Complete genome sequencing and comparative genome characterization of the lignocellulosic biomass degrading bacterium Pseudomonas stutzeri MP4687 from cattle rumen

We report the complete genome sequencing of novel Pseudomonas stutzeri strain MP4687 isolated from cattle rumen. Various strains of P. stutzeri have been reported from different environmental samples including oil-contaminated sites, crop roots, air, and human clinical samples, but not from rumen samples, which is being reported here for the first time. The genome of P. stutzeri MP4687 has a single replicon, 4.75 Mb chromosome and a G + C content of 63.45%. The genome encodes for 4,790 protein coding genes including 164 CAZymes and 345 carbohydrate processing genes. The isolate MP4687 harbors LCB hydrolyzing potential through endoglucanase (4.5 U/mL), xylanase (3.1 U/mL), β-glucosidase (3.3 U/mL) and β-xylosidase (1.9 U/mL) activities. The pangenome analysis further revealed that MP4687 has a very high number of unique genes (>2100) compared to other P. stutzeri genomes, which might have an important role in rumen functioning.

Simultaneous Enhancement of Thermostability and Catalytic Activity of a Metagenome-Derived β-Glucosidase Using Directed Evolution for the Biosynthesis of Butyl Glucoside

Butyl glucoside synthesis using bioenzymatic methods at high temperatures has gained increasing interest. Protein engineering using directed evolution of a metagenome-derived β-glucosidase of Bgl1D was performed to identify enzymes with improved activity and thermostability. An interesting mutant Bgl1D187 protein containing five amino acid substitutions (S28T, Y37H, D44E, R91G, and L115N), showed catalytic efficiency (k_cat/K_m of 561.72 mM⁻¹ s⁻¹) toward ρ-nitrophenyl-β-d-glucopyranoside (ρNPG) that increased by 23-fold, half-life of inactivation by 10-fold, and further retained transglycosidation activity at 50 °C as compared with the wild-type Bgl1D protein. Site-directed mutagenesis also revealed that Asp44 residue was essential to β-glucosidase activity of Bgl1D. This study improved our understanding of the key amino acids of the novel β-glucosidases and presented a raw material with enhanced catalytic activity and thermostability for the synthesis of butyl glucosides.

Secretion of DNases by Marine Bacteria: A Culture Based and Bioinformatics Approach

The vast majority of bacteria present in the natural environment are present in the form of aggregates and/or biofilms. Microbial aggregates are ubiquitous in the marine environment and are inhabited by diverse microbial communities which often express intense extracellular enzymatic activities. However, the secretion of an important group of enzymes, DNases, by bacteria from marine aggregates has not been studied, despite the importance of these aggregates in biogeochemical cycling of nutrients in the oceans. In this work, we therefore, employed both culture-based and bioinformatics approaches to understand the diversity of bacterial DNases in marine bacterioplankton. We found that 34% of 345 strains of attached and non-attached marine bacteria showed extracellular DNase activity. Most of these isolates belong to Proteobacteria (53%) and Firmicutes (34%). Secretion of DNases by bacteria isolated from marine gel particles (MGP) is reported here for the first time. Then, to further understand the wider diversity of the potential to produce DNases, sequences were compared using 2316 whole genome and 42 metagenome datasets. Thirty-nine different taxonomic groups corresponding to 10 bacterial phyla were found to encode genes responsible for DNase secretion. This study highlights the unexpected and widespread presence of DNase secretion in bacteria in general and in MGP more specifically. This has important implications for understanding the dynamics and fate of marine microbial aggregates in the oceans.

Harnessing Marine Biocatalytic Reservoirs for Green Chemistry Applications through Metagenomic Technologies

In a demanding commercial world, large-scale chemical processes have been widely utilised to satisfy consumer related needs. Chemical industries are key to promoting economic growth and meeting the requirements of a sustainable industrialised society. The market need for diverse commodities produced by the chemical industry is rapidly expanding globally. Accompanying this demand is an increased threat to the environment and to human health, due to waste produced by increased industrial production. This increased demand has underscored the necessity to increase reaction efficiencies, in order to reduce costs and increase profits. The discovery of novel biocatalysts is a key method aimed at combating these difficulties. Metagenomic technology, as a tool for uncovering novel biocatalysts, has great potential and applicability and has already delivered many successful achievements. In this review we discuss, recent developments and achievements in the field of biocatalysis. We highlight how green chemistry principles through the application of biocatalysis, can be successfully promoted and implemented in various industrial sectors. In addition, we demonstrate how two novel lipases/esterases were mined from the marine environment by metagenomic analysis. Collectively these improvements can result in increased efficiency, decreased energy consumption, reduced waste and cost savings for the chemical industry.

The Holo-Transcriptome of the Zoantharian Protopalythoa variabilis (Cnidaria: Anthozoa): A Plentiful Source of Enzymes for Potential Application in Green Chemistry, Industrial and Pharmaceutical Biotechnology

Marine invertebrates, such as sponges, tunicates and cnidarians (zoantharians and scleractinian corals), form functional assemblages, known as holobionts, with numerous microbes. This type of species-specific symbiotic association can be a repository of myriad valuable low molecular weight organic compounds, bioactive peptides and enzymes. The zoantharian Protopalythoa variabilis (Cnidaria: Anthozoa) is one such example of a marine holobiont that inhabits the coastal reefs of the tropical Atlantic coast and is an interesting source of secondary metabolites and biologically active polypeptides. In the present study, we analyzed the entire holo-transcriptome of P. variabilis, looking for enzyme precursors expressed in the zoantharian-microbiota assemblage that are potentially useful as industrial biocatalysts and biopharmaceuticals. In addition to hundreds of predicted enzymes that fit into the classes of hydrolases, oxidoreductases and transferases that were found, novel enzyme precursors with multiple activities in single structures and enzymes with incomplete Enzyme Commission numbers were revealed. Our results indicated the predictive expression of thirteen multifunctional enzymes and 694 enzyme sequences with partially characterized activities, distributed in 23 sub-subclasses. These predicted enzyme structures and activities can prospectively be harnessed for applications in diverse areas of industrial and pharmaceutical biotechnology.

Identification and molecular characterization of a metagenome-derived L-lysine decarboxylase gene from subtropical soil microorganisms

L-lysine decarboxylase (LDC, EC 4.1.1.18) is a key enzyme in the decarboxylation of L-lysine to 1,5-pentanediamine and efficiently contributes significance to biosynthetic capability. Metagenomic technology is a shortcut approach used to obtain new genes from uncultured microorganisms. In this study, a subtropical soil metagenomic library was constructed, and a putative LDC gene named ldc1E was isolated by function-based screening strategy through the indication of pH change by L-lysine decarboxylation. Amino acid sequence comparison and homology modeling indicated the close relation between Ldc1E and other putative LDCs. Multiple sequence alignment analysis revealed that Ldc1E contained a highly conserved motif Ser-X-His-Lys (Pxl), and molecular docking results showed that this motif was located in the active site and could combine with the cofactor pyridoxal 5'-phosphate. The ldc1E gene was subcloned into the pET-30a(+) vector and highly expressed in Escherichia coli BL21 (DE3) pLysS. The recombinant protein was purified to homogeneity. The maximum activity of Ldc1E occurred at pH 6.5 and 40°C using L-lysine monohydrochloride as the substrate. Recombinant Ldc1E had apparent Km, kcat, and kcat/Km values of 1.08±0.16 mM, 5.09±0.63 s-1, and 4.73×103 s-1 M-1, respectively. The specific activity of Ldc1E was 1.53±0.06 U mg-1 protein. Identifying a metagenome-derived LDC gene provided a rational reference for further gene modifications in industrial applications.