Characterization of Genetically Modified Microorganisms Using Short- and Long-Read Whole-Genome Sequencing Reveals Contaminations of Related Origin in Multiple Commercial Food Enzyme Products

Metagenomics-based tracing of genetically modified microorganism contaminations in commercial fermentation products

Genetically modified microorganisms (GMM) are frequently employed for the production of microbial fermentation products such as food enzymes. Although presence of the GMM or its recombinant DNA in the final product is not authorized, contaminations occur frequently. Insight into the contamination source of a GMM is of crucial importance to allow the competent authorities to take appropriate action. The aim of this study was to explore the feasibility of a metagenomic shotgun sequencing approach to investigate microbial contamination in fermentation products, focusing on source tracing of GMM strains using innovative strain deconvolution and phylogenomic approaches. In most cases, analysis of 16 GMM-contaminated food enzyme products supported finding the same GM producer strains in different products, while often multiple GMM contaminations per product were detected. Presence of AMR genes in the samples was strongly associated with GMM contamination, emphasizing the potential public health risk. Additionally, a variety of other microbial contaminations were detected, identifying a group of samples with a conspicuously similar contamination profile, which suggested that these samples originated from the same production facility or batch. Together, these findings highlight the need for guidelines and quality control for traceability of these products to ensure the safety of consumers. This study demonstrates the added value of metagenomics to obtain insight in the microbial contamination profiles, as well as their underlying relationships, in commercial microbial fermentation products. The proposed approach may be applied to other types of microbial fermentation products and/or to other (genetically modified) producer strains.

Assessing the authenticity and purity of a commercial Bacillus thuringiensis bioinsecticide through whole genome sequencing and metagenomics approaches

Biopesticides, biological agents for pest control in plants, are becoming increasingly prevalent in agricultural practices. However, no established methodology currently exists to assess their quality, and there are currently no publicly available authenticity and purity evaluations of commercial products. This lack of data may represent risks because of their widespread dispersal in the environment. We evaluated the potential of whole genome sequencing (WGS) and metagenomics approaches, including nanopore long-read sequencing, to verify both authenticity (i.e., the labeled strain) and biological purity (i.e., the absence of any undesired genetic material) of commercial Bacillus thuringiensis bioinsecticides. Four commercially available bioinsecticidal products containing Bacillus thuringiensis serovar kurstaki strain HD-1 were collected from the European market as a case study. Two sequencing approaches were employed: WGS of isolates and metagenomics sequencing of all genetic material in a product. To assess authenticity, isolate WGS data were compared against the publicly available reference genome of the expected strain. Antimicrobial resistance gene content, insecticidal gene content, and single nucleotide polymorphism differences were characterized to evaluate similarity to the reference genome. To assess purity, metagenomic sequencing data were analyzed using read classification and strain differentiation methods. Additionally, long- and short-read data were used to assess potential large-scale structural variations. Our results confirmed all investigated products to be authentic and pure. With the increasing usage of biopesticides, it is crucial to have adequate quality control methods. Our proposed approach could be adapted for other biopesticides, and similar products, providing a standardized and robust approach to contribute to biopesticide safety.

Pilot market surveillance of GMM contaminations in alpha-amylase food enzyme products: A detection strategy strengthened by a newly developed qPCR method targeting a GM Bacillus licheniformis producing alpha-amylase

Using high-throughput metagenomics on commercial microbial fermentation products, DNA from a new unauthorized genetically modified microorganism (GMM), namely the GM B. licheniformis strain producing alpha-amylase (GMM alpha-amylase2), was recently discovered and characterized. On this basis, a new qPCR method targeting an unnatural association of sequences specific to the GMM alpha-amylase2 strain was designed and developed in this study, allowing to strengthen the current GMM detection strategy. The performance of the newly developed qPCR method was assessed for its specificity and sensitivity to comply with the minimum performance requirements established by the European Network of GMO Laboratories for GMO analysis. Moreover, the transferability of the in house validated qPCR method was demonstrated. Finally, its applicability was confirmed by a pilot market surveillance of GMM contaminations conducted for the first time on 40 alpha-amylase food enzyme products labelled as containing alpha-amylase. This pilot market surveillance allowed also to highlight numerous contaminations with GMM alpha-amylase2, including frequent cross-contaminations with other GMM strains previously characterized. In addition, the presence of full-length AMR genes, raising health concerns, was also reported.

Comparison of 6 DNA extraction methods for isolation of high yield of high molecular weight DNA suitable for shotgun metagenomics Nanopore sequencing to detect bacteria

BACKGROUND

Oxford Nanopore Technologies (ONT) offers an accessible platform for long-read sequencing, which improves the reconstruction of genomes and helps to resolve complex genomic contexts, especially in the case of metagenome analysis. To take the best advantage of long-read sequencing, DNA extraction methods must be able to isolate pure high molecular weight (HMW) DNA from complex metagenomics samples, without introducing any bias. New methods released on the market, and protocols developed at the research level, were specifically designed for this application and need to be assessed.

RESULTS

In this study, with different bacterial cocktail mixes, analyzed as pure or spiked in a synthetic fecal matrix, we evaluated the performances of 6 DNA extraction methods using various cells lysis and purification techniques, from quick and easy, to more time-consuming and gentle protocols, including a portable method for on-site application. In addition to the comparison of the quality, quantity and purity of the extracted DNA, the performance obtained when doing Nanopore sequencing on a MinION flow cell was also tested. From the obtained results, the Quick-DNA HMW MagBead Kit (Zymo Research) was selected as producing the best yield of pure HMW DNA. Furthermore, this kit allowed an accurate detection, by Nanopore sequencing, of almost all the bacterial species present in a complex mock community.

CONCLUSION

Amongst the 6 tested methods, the Quick-DNA HMW MagBead Kit (Zymo Research) was considered as the most suitable for Nanopore sequencing and would be recommended for bacterial metagenomics studies using this technology.

Metagenomic Characterization of Multiple Genetically Modified Bacillus Contaminations in Commercial Microbial Fermentation Products

Genetically modified microorganisms (GMM) are frequently employed for manufacturing microbial fermentation products such as food enzymes or vitamins. Although the fermentation product is required to be pure, GMM contaminations have repeatedly been reported in numerous commercial microbial fermentation produce types, leading to several rapid alerts at the European level. The aim of this study was to investigate the added value of shotgun metagenomic high-throughput sequencing to confirm and extend the results of classical analysis methods for the genomic characterization of unauthorized GMM. By combining short- and long-read metagenomic sequencing, two transgenic constructs were characterized, with insertions of alpha-amylase genes originating from B. amyloliquefaciens and B. licheniformis, respectively, and a transgenic construct with a protease gene insertion originating from B. velezensis, which were all present in all four investigated samples. Additionally, the samples were contaminated with up to three unculturable Bacillus strains, carrying genetic modifications that may hamper their ability to sporulate. Moreover, several samples contained viable Bacillus strains. Altogether these contaminations constitute a considerable load of antimicrobial resistance genes, that may represent a potential public health risk. In conclusion, our study showcases the added value of metagenomics to investigate the quality and safety of complex commercial microbial fermentation products.