Tag: Single-cell sequencing

As the 8th Next Generation Sequencing Congress in London is drawing to a close as I write this, I have a few reflections that might warrant sharing. The first thing that has been apparent this year compared to the two previous times I have visited the event (in 2012 and 2013) is that there was very little talk about where Illumina sequencing is heading next. Instead the discussion was about the applications of Illumina sequencing in the clinical setting; so apparently this is now so mainstream that we only expect slow progress towards longer reads. Apart from that, Illumina is a completed, mature technology. Instead, the flashlight is now pointing entirely towards long-read sequencing (PacBio, NanoPore) as the next big thing. However, the excitement around these technologies has also sort of faded compared to in 2013 when they were soon-to-arrive. Indeed, it seems like there’s not much to be excited about in the sequencing field at the moment, or at least Oxford Global (who are hosting the conference) has failed to get these technologies here.

What also strikes me is the vast amounts of talk about RNAseq of cancer cells. The scope of this event has narrowed dramatically in the past three years. Which makes me substantially less interested in returning next year. If there is not much to be excited about, and the focus is only on cancer sequencing – despite the human microbiota being a very hot topic at the moment – what is the reason for non-cancer researchers to come to the event? There will need to be a stark shift towards another direction of this event if the arrangers want it to remain a broad NGS event. Otherwise, they may just as well go all in and rename the event the Next Generation Sequencing of Cancer Congress. But I hope they choose to widen the scope again; conferences discussing technology as a foundation for a variety of applications are important meeting points and spawning grounds for novel ideas.

In a recent Nature article (1), Craig Venter and his co-workers at JCVI has not only sequenced one marine bacterium, but 137 different isolates. Their main goal of this study was to better understand the ecology of marine picoplankton in the context of Global Ocean Sampling (GOS) data (2,3). As I see it, there are at least two really interesting things going on here:

First, this is a milestone in sequencing. Were not talking one genome – one article anymore. Were talking one article – 137 new genomes. This vastly raises the bar for any sequencing efforts in the future, but even more importantly, it shifts the focus even further from the actual sequencing to the purpose of the sequencing. One sequenced genome might be interesting enough if it fills a biological knowledge gap, but just sequencing a bacterial strain isn’t worth that much anymore. With the arrival of second- and third-generation sequencing techniques, this development was pretty obvious, but this article is (to my knowledge) the first real proof of that this has finally happened. I expect that five to ten years from now, not sequencing an organism of interest for your research will be viewed as very strange and backwards-looking. “Why didn’t you sequence this?” will be a highly relevant review question for many publications. But also the days when you could write “we here publish for the first time the complete genome sequence of <insert organism name here>” and have that as the central theme for an article will soon be over. Sequencing will simply be reduced to the (valuable) tool it actually is. Which is probably good, as it brings us back to biology again. Articles like this one, where you look at ~200 genomes to investigate ecological questions, are simply providing a more relevant biological perspective than staring at the sequence of one genome in a time when DNA-data is flooding over us.

Second, this is the first (again, to my knowledge) publication where questions arising from metagenomics (2,3,4) has initiated a huge sequencing effort to understand the ecology or the environment to which the metagenome is associated. This highlights a new use of metagenomics as a prospective technique, to mine various environments for interesting features, and then select a few of its inhabitants and look closer at who is responsible for what. With a number of emerging single cell sequencing and visualisation techniques (5,6,7,8) as well as the application of cell sorting approaches to environmental communities (5,9), we can expect metagenomics to play a huge role in organism, strain and protein discovery, but also in determining microbial ecosystem services. Though Venter’s latest article (1) is just a first step towards this new role for metagenomics, it’s a nice example of what (meta)genomics could look like towards the end of this decade, if even not sooner.

1. Yooseph et al. Genomic and functional adaptation in surface ocean planktonic prokaryotes. Nature (2010) vol. 468 (7320) pp. 60-6
2. Yooseph et al. The Sorcerer II Global Ocean Sampling expedition: expanding the universe of protein families. Plos Biol (2007) vol. 5 (3) pp. e16
3. Rusch et al. The Sorcerer II Global Ocean Sampling expedition: northwest Atlantic through eastern tropical Pacific. Plos Biol (2007) vol. 5 (3) pp. e77
4. Rusch et al. Characterization of Prochlorococcus clades from iron-depleted oceanic regions. Proceedings of the National Academy of Sciences of the United States of America (2010) pp.
5. Woyke et al. Assembling the marine metagenome, one cell at a time. PLoS ONE (2009) vol. 4 (4) pp. e5299
6. Woyke et al. One bacterial cell, one complete genome. PLoS ONE (2010) vol. 5 (4) pp. e10314
7. Moraru et al. GeneFISH – an in situ technique for linking gene presence and cell identity in environmental microorganisms. Environ Microbiol (2010) pp.
8. Lasken. Genomic DNA amplification by the multiple displacement amplification (MDA) method. Biochem Soc Trans (2009) vol. 37 (Pt 2) pp. 450-3
9. Mary et al. Metaproteomic and metagenomic analyses of defined oceanic microbial populations using microwave cell fixation and flow cytometric sorting. FEMS microbiology ecology (2010) pp.