Evaluation of a pooled strategy for high-throughput sequencing of cosmid clones from metagenomic libraries

High-throughput nanopore DNA sequencing of large insert fosmid clones directly from bacterial colonies

Fosmids and cosmids are vectors frequently used in functional metagenomic studies. With a large insert capacity (around 30 kb) they can encode dozens of cloned genes or in some cases, entire biochemical pathways. Fosmids with cloned inserts can be transferred to heterologous hosts and propagated to enable screening for new enzymes and metabolites. After screening, fosmids from clones with an activity of interest must be de novo sequenced, a critical step toward the identification of the gene(s) of interest. In this work, we present a new approach for rapid and high-throughput fosmid sequencing directly from Escherichia coli colonies without liquid culturing or fosmid purification. Our sample preparation involves fosmid amplification with phi29 polymerase and then direct nanopore sequencing using the Oxford Nanopore Technologies system. We also present a bioinformatics pipeline termed "phiXXer" that facilitates both de novo read assembly and vector trimming to generate a linear sequence of the fosmid insert. Finally, we demonstrate the accurate sequencing of 96 fosmids in a single run and validate the method using two fosmid libraries that contain cloned large insert (~30-40 kb) genomic or metagenomic DNA.IMPORTANCELarge-insert clone (fosmids or cosmids) sequencing is challenging and arguably the most limiting step of functional metagenomic screening workflows. Our study establishes a new method for high-throughput nanopore sequencing of fosmid clones directly from lysed Escherichia coli cells. It also describes a companion bioinformatic pipeline that enables de novo assembly of fosmid DNA insert sequences. The devised method widens the potential of functional metagenomic screening by providing a simple, high-throughput approach to fosmid clone sequencing that dramatically speeds the pace of discovery.

Arabinan saccharification by biogas reactor metagenome-derived arabinosyl hydrolases

BACKGROUND

Plant cell walls represent the most plentiful renewable organic resource on earth, but due to their heterogeneity, complex structure and partial recalcitrance, their use as biotechnological feedstock is still limited.

RESULTS

In order to identify efficient enzymes for polysaccharide breakdown, we have carried out functional screening of metagenomic fosmid libraries from biogas fermenter microbial communities grown on sugar beet pulp, an arabinan-rich agricultural residue, or other sources containing microbes that efficiently depolymerize polysaccharides, using CPH (chromogenic polysaccharide hydrogel) or ICB (insoluble chromogenic biomass) labeled polysaccharide substrates. Seventy-one depolymerase-encoding genes were identified from 55 active fosmid clones by using Illumina and Sanger sequencing and dbCAN CAZyme (carbohydrate-active enzyme) annotation. An around 56 kb assembled DNA fragment putatively originating from Xylanivirga thermophila strain or a close relative was analyzed in detail. It contained 48 ORFs (open reading frames), of which 31 were assigned to sugar metabolism. Interestingly, a large number of genes for enzymes putatively involved in degradation and utilization of arabinose-containing carbohydrates were found. Seven putative arabinosyl hydrolases from this DNA fragment belonging to glycoside hydrolase (GH) families GH51 and GH43 were biochemically characterized, revealing two with endo-arabinanase activity and four with exo-α-L-arabinofuranosidase activity but with complementary cleavage properties. These enzymes were found to act synergistically and can completely hydrolyze SBA (sugar beet arabinan) and DA (debranched arabinan).

CONCLUSIONS

We screened 32,776 fosmid clones from several metagenomic libraries with chromogenic lignocellulosic substrates for functional enzymes to advance the understanding about the saccharification of recalcitrant lignocellulose. Seven putative X. thermophila arabinosyl hydrolases were characterized for pectic substrate degradation. The arabinosyl hydrolases displayed maximum activity and significant long-term stability around 50 °C. The enzyme cocktails composed in this study fully degraded the arabinan substrates and thus could serve for arabinose production in food and biofuel industries.

A Meta-Omics Analysis Unveils the Shift in Microbial Community Structures and Metabolomics Profiles in Mangrove Sediments Treated with a Selective Actinobacterial Isolation Procedure

Mangrove sediment ecosystems in the coastal areas of the Yucatan peninsula are unique environments, influenced by their karstic origin and connection with the world’s largest underground river. The microbial communities residing in these sediments are influenced by the presence of mangrove roots and the trading chemistry for communication between sediment bacteria and plant roots can be targeted for secondary metabolite research. To explore the secondary metabolite production potential of microbial community members in mangrove sediments at the “El Palmar” natural reserve in Sisal, Yucatan, a combined meta-omics approach was applied. The effects of a cultivation medium reported to select for actinomycetes within mangrove sediments’ microbial communities was also analyzed. The metabolome of the microbial communities was analyzed by high-resolution liquid chromatography-tandem mass spectrometry, and molecular networking analysis was used to investigate if known natural products and their variants were present. Metagenomic results suggest that the sediments from “El Palmar” harbor a stable bacterial community independently of their distance from mangrove tree roots. An unexpected decrease in the observed abundance of actinomycetes present in the communities occurred when an antibiotic-amended medium considered to be actinomycete-selective was applied for a 30-day period. However, the use of this antibiotic-amended medium also enhanced production of secondary metabolites within the microbial community present relative to the water control, suggesting the treatment selected for antibiotic-resistant bacteria capable of producing a higher number of secondary metabolites. Secondary metabolite mining of “El Palmar” microbial community metagenomes identified polyketide synthase and non-ribosomal peptide synthetases’ biosynthetic genes in all analyzed metagenomes. The presence of these genes correlated with the annotation of several secondary metabolites from the Global Natural Product Social Molecular Networking database. These results highlight the biotechnological potential of the microbial communities from “El Palmar”, and show the impact selective media had on the composition of communities of actinobacteria.

MINTIA: a metagenomic INserT integrated assembly and annotation tool

The earth harbors trillions of bacterial species adapted to very diverse ecosystems thanks to specific metabolic function acquisition. Most of the genes responsible for these functions belong to uncultured bacteria and are still to be discovered. Functional metagenomics based on activity screening is a classical way to retrieve these genes from microbiomes. This approach is based on the insertion of large metagenomic DNA fragments into a vector and transformation of a host to express heterologous genes. Metagenomic libraries are then screened for activities of interest, and the metagenomic DNA inserts of active clones are extracted to be sequenced and analysed to identify genes that are responsible for the detected activity. Hundreds of metagenomics sequences found using this strategy have already been published in public databases. Here we present the MINTIA software package enabling biologists to easily generate and analyze large metagenomic sequence sets, retrieved after activity-based screening. It filters reads, performs assembly, removes cloning vector, annotates open reading frames and generates user friendly reports as well as files ready for submission to international sequence repositories. The software package can be downloaded from https://github.com/Bios4Biol/MINTIA.

Combining functional metagenomics and glycoanalytics to identify enzymes that facilitate structural characterization of sulfated N-glycans

BACKGROUND

Sulfate modification of N-glycans is important for several biological functions such as clearance of pituitary hormones or immunoregulation. Yet, the prevalence of this N-glycan modification and its functions remain largely unexplored. Characterization of N-glycans bearing sulfate modifications is hampered in part by a lack of enzymes that enable site-specific detection of N-glycan sulfation. In this study, we used functional metagenomic screening to identify enzymes that act upon sulfated N-acetylglucosamine (GlcNAc). Using multiplexed capillary gel electrophoresis with laser-induced fluorescence detection (xCGE-LIF) -based glycoanalysis we proved their ability to act upon GlcNAc-6-SO4 on N-glycans.

RESULTS

Our screen identified a sugar-specific sulfatase that specifically removes sulfate from GlcNAc-6-SO4 when it is in a terminal position on an N-glycan. Additionally, in the absence of calcium, this sulfatase binds to the sulfated glycan but does not remove the sulfate group, suggesting it could be used for selective isolation of sulfated N-glycans. Further, we describe isolation of a sulfate-dependent hexosaminidase that removes intact GlcNAc-6-SO4 (but not asulfated GlcNAc) from a terminal position on N-glycans. Finally, the use of these enzymes to detect the presence of sulfated N-glycans by xCGE-LIF is demonstrated.

CONCLUSION

The present study demonstrates the feasibility of using functional metagenomic screening combined with glycoanalytics to discover enzymes that act upon chemical modifications of glycans. The discovered enzymes represent new specificities that can help resolve the presence of GlcNAc-6-SO4 in N-glycan structural analyses.

Recovery and functional validation of hidden soil enzymes in metagenomic libraries

The vast microbial diversity on the planet represents an invaluable source for identifying novel activities with potential industrial and therapeutic application. In this regard, metagenomics has emerged as a group of strategies that have significantly facilitated the analysis of DNA from multiple environments and has expanded the limits of known microbial diversity. However, the functional characterization of enzymes, metabolites, and products encoded by diverse microbial genomes is limited by the inefficient heterologous expression of foreign genes. We have implemented a pipeline that combines NGS and Sanger sequencing as a way to identify fosmids within metagenomic libraries. This strategy facilitated the identification of putative proteins, subcloning of targeted genes and preliminary characterization of selected proteins. Overall, the in silico approach followed by the experimental validation allowed us to efficiently recover the activity of previously hidden enzymes derived from agricultural soil samples. Therefore, the methodology workflow described herein can be applied to recover activities encoded by environmental DNA from multiple sources.

A-GAME: improving the assembly of pooled functional metagenomics sequence data

Background

Expression screening of environmental DNA (eDNA) libraries is a popular approach for the identification and characterization of novel microbial enzymes with promising biotechnological properties. In such “functional metagenomics” experiments, inserts, selected on the basis of activity assays, are sequenced with high throughput sequencing technologies. Assembly is followed by gene prediction, annotation and identification of candidate genes that are subsequently evaluated for biotechnological applications.

Results

Here we present A-GAME (A GAlaxy suite for functional MEtagenomics), a web service incorporating state of the art tools and workflows for the analysis of eDNA sequence data. We illustrate the potential of A-GAME workflows using real functional metagenomics data, showing that they outperform alternative metagenomics assemblers. Dedicated tools available in A-GAME allow efficient analysis of pooled libraries and rapid identification of candidate genes, reducing sequencing costs and saving the need for laborious manual annotation.

Conclusion

In conclusion, we believe A-GAME will constitute a valuable resource for the functional metagenomics community.

A-GAME is publicly available at http://beaconlab.it/agame

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4369-z) contains supplementary material, which is available to authorized users.

Discovery of carbamate degrading enzymes by functional metagenomics

Bioremediation of pollutants is a major concern worldwide, leading to the research of new processes to break down and recycle xenobiotics and environment contaminating polymers. Among them, carbamates have a very broad spectrum of uses, such as toxinogenic pesticides or elastomers. In this study, we mined the bovine rumen microbiome for carbamate degrading enzymes. We isolated 26 hit clones exhibiting esterase activity, and were able to degrade at least one of the targeted polyurethane and pesticide carbamate compounds. The most active clone was deeply characterized. In addition to Impranil, this clone was active on Tween 20, pNP-acetate, butyrate and palmitate, and on the insecticide fenobucarb. Sequencing and sub-cloning of the best target revealed a novel carboxyl-ester hydrolase belonging to the lipolytic family IV, named CE_Ubrb. This study highlights the potential of highly diverse microbiota such as the ruminal one for the discovery of promiscuous enzymes, whose versatility could be exploited for industrial uses.

A metagenome-derived thermostable β-glucanase with an unusual module architecture which defines the new glycoside hydrolase family GH148

The discovery of novel and robust enzymes for the breakdown of plant biomass bears tremendous potential for the development of sustainable production processes in the rapidly evolving new bioeconomy. By functional screening of a metagenomic library from a volcano soil sample a novel thermostable endo-β-glucanase (EngU) which is unusual with regard to its module architecture and cleavage specificity was identified. Various recombinant EngU variants were characterized. Assignment of EngU to an existing glycoside hydrolase (GH) family was not possible. Two regions of EngU showed weak sequence similarity to proteins of the GH clan GH-A, and acidic residues crucial for catalytic activity of EngU were identified by mutation. Unusual, a carbohydrate-binding module (CBM4) which displayed binding affinity for β-glucan, lichenin and carboxymethyl-cellulose was found as an insertion between these two regions. EngU hydrolyzed β-1,4 linkages in carboxymethyl-cellulose, but displayed its highest activity with mixed linkage (β-1,3-/β-1,4-) glucans such as barley β-glucan and lichenin, where in contrast to characterized lichenases cleavage occurred predominantly at the β-1,3 linkages of C4-substituted glucose residues. EngU and numerous related enzymes with previously unknown function represent a new GH family of biomass-degrading enzymes within the GH-A clan. The name assigned to the new GH family is GH148.

Functional metagenomics reveals novel β-galactosidases not predictable from gene sequences

The techniques of metagenomics have allowed researchers to access the genomic potential of uncultivated microbes, but there remain significant barriers to determination of gene function based on DNA sequence alone. Functional metagenomics, in which DNA is cloned and expressed in surrogate hosts, can overcome these barriers, and make important contributions to the discovery of novel enzymes. In this study, a soil metagenomic library carried in an IncP cosmid was used for functional complementation for β-galactosidase activity in both Sinorhizobium meliloti (α-Proteobacteria) and Escherichia coli (γ-Proteobacteria) backgrounds. One β-galactosidase, encoded by six overlapping clones that were selected in both hosts, was identified as a member of glycoside hydrolase family 2. We could not identify ORFs obviously encoding possible β-galactosidases in 19 other sequenced clones that were only able to complement S. meliloti. Based on low sequence identity to other known glycoside hydrolases, yet not β-galactosidases, three of these ORFs were examined further. Biochemical analysis confirmed that all three encoded β-galactosidase activity. Lac36W_ORF11 and Lac161_ORF7 had conserved domains, but lacked similarities to known glycoside hydrolases. Lac161_ORF10 had neither conserved domains nor similarity to known glycoside hydrolases. Bioinformatic and structural modeling implied that Lac161_ORF10 protein represented a novel enzyme family with a five-bladed propeller glycoside hydrolase domain. By discovering founding members of three novel β-galactosidase families, we have reinforced the value of functional metagenomics for isolating novel genes that could not have been predicted from DNA sequence analysis alone.

Potential of semiarid soil from Caatinga biome as a novel source for mining lignocellulose-degrading enzymes

The litterfall is the major organic material deposited in soil of Brazilian Caatinga biome, thus providing the ideal conditions for plant biomass-degrading microorganisms to thrive. Herein, the phylogenetic composition and lignocellulose-degrading capacity have been explored for the first time from a fosmid library dataset of Caatinga soil by sequence-based screening. A complex bacterial community dominated by Proteobacteria and Actinobacteria was unraveled. SEED subsystems-based annotations revealed a broad range of genes assigned to carbohydrate and aromatic compounds metabolism, indicating microbial ability to utilize plant-derived material. CAZy-based annotation identified 7275 genes encoding 37 glycoside hydrolases (GHs) families related to hydrolysis of cellulose, hemicellulose, oligosaccharides and other lignin-modifying enzymes. Taxonomic affiliation of genes showed high genetic potential of the phylum Acidobacteria for hemicellulose degradation, whereas Actinobacteria members appear to play an important role in celullose hydrolysis. Additionally, comparative analyses revealed greater GHs profile similarity among soils as compared to the digestive tract of animals capable of digesting plant biomass, particularly in the hemicellulases content. Combined results suggest a complex synergistic interaction of community members required for biomass degradation into fermentable sugars. This large repertoire of lignocellulolytic enzymes opens perspectives for mining potential candidates of biochemical catalysts for biofuels production from renewable resources and other environmental applications.

Novel polyhydroxyalkanoate copolymers produced in Pseudomonas putida by metagenomic polyhydroxyalkanoate synthases

Bacterially produced biodegradable polyhydroxyalkanoates (PHAs) with versatile properties can be achieved using different PHA synthases (PhaCs). This work aims to expand the diversity of known PhaCs via functional metagenomics and demonstrates the use of these novel enzymes in PHA production. Complementation of a PHA synthesis-deficient Pseudomonas putida strain with a soil metagenomic cosmid library retrieved 27 clones expressing either class I, class II, or unclassified PHA synthases, and many did not have close sequence matches to known PhaCs. The composition of PHA produced by these clones was dependent on both the supplied growth substrates and the nature of the PHA synthase, with various combinations of short-chain-length (SCL) and medium-chain-length (MCL) PHA. These data demonstrate the ability to isolate diverse genes for PHA synthesis by functional metagenomics and their use for the production of a variety of PHA polymer and copolymer mixtures.

Strong spurious transcription likely contributes to DNA insert bias in typical metagenomic clone libraries

BACKGROUND

Clone libraries provide researchers with a powerful resource to study nucleic acid from diverse sources. Metagenomic clone libraries in particular have aided in studies of microbial biodiversity and function, and allowed the mining of novel enzymes. Libraries are often constructed by cloning large inserts into cosmid or fosmid vectors. Recently, there have been reports of GC bias in fosmid metagenomic libraries, and it was speculated to be a result of fragmentation and loss of AT-rich sequences during cloning. However, evidence in the literature suggests that transcriptional activity or gene product toxicity may play a role.

RESULTS

To explore possible mechanisms responsible for sequence bias in clone libraries, we constructed a cosmid library from a human microbiome sample and sequenced DNA from different steps during library construction: crude extract DNA, size-selected DNA, and cosmid library DNA. We confirmed a GC bias in the final cosmid library, and we provide evidence that the bias is not due to fragmentation and loss of AT-rich sequences but is likely occurring after DNA is introduced into Escherichia coli. To investigate the influence of strong constitutive transcription, we searched the sequence data for promoters and found that rpoD/σ(70) promoter sequences were underrepresented in the cosmid library. Furthermore, when we examined the genomes of taxa that were differentially abundant in the cosmid library relative to the original sample, we found the bias to be more correlated with the number of rpoD/σ(70) consensus sequences in the genome than with simple GC content.

CONCLUSIONS

The GC bias of metagenomic libraries does not appear to be due to DNA fragmentation. Rather, analysis of promoter sequences provides support for the hypothesis that strong constitutive transcription from sequences recognized as rpoD/σ(70) consensus-like in E. coli may lead to instability, causing loss of the plasmid or loss of the insert DNA that gives rise to the transcription. Despite widespread use of E. coli to propagate foreign DNA in metagenomic libraries, the effects of in vivo transcriptional activity on clone stability are not well understood. Further work is required to tease apart the effects of transcription from those of gene product toxicity.