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Sunday, July 14, 2013

The concept “Dark Matter” slides into meaninglessness

The term “dark matter” refers to a specific sort of matter in cosmology that is inferred, but not seen. Nobody knows what it consists of in any meaningful way.

But now we have the headline in Nature:

Researchers glimpse microbial 'dark matter'

Does this mean that we have found microbes that consist of the cosmological dark matter? How could this be possible?  The answer is much more mundane: the term is being borrowed and has a completely different meaning in biological science.

Single-cell sequencing enables scientists to decipher the genome of just one cell by amplifying its DNA by 1-billion-fold, opening the way to studying ‘microbial dark matter’. These are organisms that have been discovered through methods such as metagenomics studies — which examine batches of micro-organisms living in a common environment — but are difficult or impossible to grow in the lab.

Woyke and her group attempted to explore this dark matter by selecting a highly diverse range of microbes and sequencing a portion of their genomes (which could range from less than 10% to more than 90% depending on the cell). The sequences clarified the microbes’ relationships to one another and to other species.

OK, this is likely very impressive (I don’t have enough knowledge in this field to tell) but this is basically defining “dark matter” as “micro-organisms that can’t be cultivated using current laboratory techniques'”. This is a much different idea. In fact, since the study shows how these organisms can be sequenced, by the end of the study they aren’t really dark (as in unknown),  even though they still can’t be grown in the lab.

What next? Is the dark matter of my statistics course the exam questions most students miss?