A low-cost genomics workflow enables isolate screening and strain-level analyses within microbiomes

HiBC: a publicly available collection of bacterial strains isolated from the human gut

Numerous bacteria in the human gut microbiome remain unknown and/or have yet to be cultured. While collections of human gut bacteria have been published, few strains are accessible to the scientific community. We have therefore created a publicly available collection of bacterial strains isolated from the human gut. The Human intestinal Bacteria Collection (HiBC) ( https://www.hibc.rwth-aachen.de ) contains 340 strains representing 198 species within 29 families and 7 phyla, of which 29 previously unknown species are taxonomically described and named. These included two butyrate-producing species of Faecalibacterium and new dominant species associated with health and inflammatory bowel disease, Ruminococcoides intestinale and Blautia intestinihominis, respectively. Plasmids were prolific within the HiBC isolates, with almost half (46%) of strains containing plasmids, with a maximum of six within a strain. This included a broadly occurring plasmid (pBAC) that exists in three diverse forms across Bacteroidales species. Megaplasmids were identified within two strains, the pMMCAT megaplasmid is globally present within multiple Bacteroidales species. This collection of easily searchable and publicly available gut bacterial isolates will facilitate functional studies of the gut microbiome.

Enabling next-generation anaerobic cultivation through biotechnology to advance functional microbiome research

Microbiomes are complex communities of microorganisms that are essential for biochemical processes on Earth and for the health of humans, animals and plants. Many environmental and host-associated microbiomes are dominated by anaerobic microbes, some of which cannot tolerate oxygen. Anaerobic microbial communities have been extensively studied over the last 20 years using molecular techniques, especially next-generation sequencing. However, there is a renewed interest in microbial cultivation because isolates provide the basis for understanding the taxonomic and functional units of biodiversity, elucidating novel biochemical pathways and the mechanisms underlying microbe-microbe and microbe-host interactions and opening new avenues for biotechnological and clinical applications. In this Perspective, we present areas of research and applications that will benefit from advancement in anaerobic microbial cultivation. We highlight key technical and infrastructural hurdles associated with the development and deployment of sophisticated cultivation workflows. Improving the performance of cultivation techniques will set new trends in functional microbiome research in the coming years.

Scalable genotyping of microbial colonies

The sequence of the 16S region is taxonomically informative and widely used for genotyping microbes. While it is easy and inexpensive to genotype several isolates by Sanger sequencing the 16S region, this method becomes quite costly if scaled to many isolates. High-throughput sequencing provides one potential avenue for obtaining 16S sequences at scale but presents additional challenges. First, DNA purification workflows for high-throughput sample preparation are labour-intensive and expensive. Second, cost-effective multiplexing and library preparation schemes are difficult to implement for many libraries on a single sequencing run. Therefore, we implemented a scalable protocol for isolate genotyping involving colony polymerase chain reaction (PCR) with simple cell lysis as well as a four-barcode indexing scheme that enables scalable multiplexing and streamlined library preparation by amplifying with four primers simultaneously in a single reaction. We tested this protocol on 93 colonies cultured from environmental samples, and we were able to ascertain the identity of ~90% of microbial isolates.

Removal of sequencing adapter contamination improves microbial genome databases

Advances in assembling microbial genomes have led to growth of reference genome databases, which have been transformative for applied and basic microbiome research. Here we show that published microbial genome databases from humans, mice, cows, pigs, fish, honeybees, and marine environments contain significant sequencing-adapter contamination that systematically reduces assembly accuracy and contiguousness. By removing the adapter-contaminated ends of contiguous sequences and reassembling MGnify reference genomes, we improve the quality of assemblies in these databases.

Hackflex library preparation enables low-cost metagenomic profiling

Shotgun metagenomic sequencing provides valuable insights into microbial communities, but the high cost of library preparation with standard kits and protocols is a barrier for many. New methods such as Hackflex use diluted commercially available reagents to greatly reduce library preparation costs. However, these methods have not been systematically validated for metagenomic sequencing. Here, we evaluate Hackflex performance by sequencing metagenomic libraries from known mock communities as well as mouse fecal samples prepared by Hackflex, Illumina DNA Prep, and Illumina TruSeq methods. Hackflex successfully recovered all members of the Zymo mock community, performing best for samples with DNA concentrations <1 ng/uL. Furthermore, Hackflex was able to delineate microbiota of individual inbred mice from the same breeding stock at the same mouse facility, and statistical modeling indicated that mouse ID explained a greater fraction of the variance in metagenomic composition than did library preparation method. These results show that Hackflex is suitable for generating inventories of bacterial communities through metagenomic sequencing.

High-throughput DNA extraction and cost-effective miniaturized metagenome and amplicon library preparation of soil samples for DNA sequencing

Reductions in sequencing costs have enabled widespread use of shotgun metagenomics and amplicon sequencing, which have drastically improved our understanding of the microbial world. However, large sequencing projects are now hampered by the cost of library preparation and low sample throughput, comparatively to the actual sequencing costs. Here, we benchmarked three high-throughput DNA extraction methods: ZymoBIOMICS™ 96 MagBead DNA Kit, MP BiomedicalsTM FastDNATM-96 Soil Microbe DNA Kit, and DNeasy® 96 PowerSoil® Pro QIAcube® HT Kit. The DNA extractions were evaluated based on length, quality, quantity, and the observed microbial community across five diverse soil types. DNA extraction of all soil types was successful for all kits, however DNeasy® 96 PowerSoil® Pro QIAcube® HT Kit excelled across all performance parameters. We further used the nanoliter dispensing system I.DOT One to miniaturize Illumina amplicon and metagenomic library preparation volumes by a factor of 5 and 10, respectively, with no significant impact on the observed microbial communities. With these protocols, DNA extraction, metagenomic, or amplicon library preparation for one 96-well plate are approx. 3, 5, and 6 hours, respectively. Furthermore, the miniaturization of amplicon and metagenome library preparation reduces the chemical and plastic costs from 5.0 to 3.6 and 59 to 7.3 USD pr. sample. This enhanced efficiency and cost-effectiveness will enable researchers to undertake studies with greater sample sizes and diversity, thereby providing a richer, more detailed view of microbial communities and their dynamics.

Diverse Prophage Elements of Salmonella enterica Serovars Show Potential Roles in Bacterial Pathogenicity

Nontyphoidal salmonellosis is an important foodborne and zoonotic infection that causes significant global public health concern. Diverse serovars are multidrug-resistant and encode several virulence indicators; however, little is known on the role prophages play in driving these traits. Here, we extracted prophages from seventy-five Salmonella genomes which represent the fifteen important serovars in the United Kingdom. We analyzed the intact prophages for the presence of virulence genes and established their genomic relationships. We identified 615 prophages from the Salmonella strains, from which 195 prophages are intact, 332 are incomplete, while 88 are questionable. The average prophage carriage was found to be 'extreme' in S. Heidelberg, S. Inverness, and S. Newport (10.2-11.6 prophages/strain), 'high' in S. Infantis, S. Stanley, S. Typhimurium, and S. Virchow (8.2-9.0 prophages/strain), 'moderate' in S. Agona, S. Braenderup, S. Bovismorbificans, S. Choleraesuis, S. Dublin, and S. Java (6.0-7.8 prophages/strain), and 'low' in S. Javiana and S. Enteritidis (5.8 prophages/strain). Cumulatively, 61 virulence genes (1500 gene copies) were detected from representative intact prophages and linked to Salmonella delivery/secretion system (42.62%), adherence (32.7%), magnesium uptake (3.88%), regulation (5%), stress/survival (1.6%), toxins (10%), and antivirulence (1.6%). Diverse clusters were formed among the intact prophages and with bacteriophages of other enterobacteria, suggesting different lineages and associations. Our work provides a strong body of data to support the contributions diverse prophages make to the pathogenicity of Salmonella, including thirteen previously unexplored serovars.

Hackflex library preparation enables low-cost metagenomic profiling

Shotgun metagenomic sequencing provides valuable insights into microbial communities, but the high cost of library preparation with standard kits and protocols is a barrier for many. New methods such as Hackflex use diluted commercially available reagents to greatly reduce library preparation costs. However, these methods have not been systematically validated for metagenomic sequencing. Here, we evaluate Hackflex performance by sequencing metagenomic libraries from known mock communities as well as mouse fecal samples prepared by Hackflex, Illumina DNA Prep, and Illumina TruSeq methods. Hackflex successfully recovered all members of the Zymo mock community, performing best for samples with DNA concentrations <1 ng/μL. Furthermore, Hackflex was able to delineate microbiota of individual inbred mice from the same breeding stock at the same mouse facility, and statistical modeling indicated that mouse ID explained a greater fraction of the variance in metagenomic composition than did library preparation method. These results show that Hackflex is suitable for generating inventories of bacterial communities through metagenomic sequencing.

Technical upgrade of an open-source liquid handler to support bacterial colony screening

The optimization of genetically engineered biological constructs is a key step to deliver high-impact biotechnological applications. The use of high-throughput DNA assembly methods allows the construction of enough genotypic variants to successfully cover the target design space. This, however, entails extra workload for researchers during the screening stage of candidate variants. Despite the existence of commercial colony pickers, their high price excludes small research laboratories and budget-adjusted institutions from accessing such extensive screening capability. In this work we present COPICK, a technical solution to automatize colony picking in an open-source liquid handler Opentrons OT-2. COPICK relies on a mounted camera to capture images of regular Petri dishes and detect microbial colonies for automated screening. COPICK's software can then automatically select the best colonies according to different criteria (size, color and fluorescence) and execute a protocol to pick them for further analysis. Benchmark tests performed for E. coli and P. putida colonies delivers a raw picking performance over pickable colonies of 82% with an accuracy of 73.4% at an estimated rate of 240 colonies/h. These results validate the utility of COPICK, and highlight the importance of ongoing technical improvements in open-source laboratory equipment to support smaller research teams.