For the publicJourney to the Centre of the Earth: the first 23cm

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The BLAST Game

This bioinformatics tool is called BLAST (Basic Local Alignment Search Tool) which is used to compare a sequence to the large public National Center for Biotechnology Information (NCBI) database where all published and much unpublished sequence data is kept ( Type a DNA nucleotide sequence into the box to discover the organism that the sequence came from.

Download an Adobe Acrobat PDF file of the Top Trump cards used in this game



Abundance is the number in a square metre of soil to a depth of 23 cm.
Trophic group refers to role in food chain: group 4 organisms are predators that eat group 3, 3 are predators that eat 2, 2 are scavengers that eat 1, 1 are primary nutrient sources (producers).
Width in Ám (microns) is the easiest way to compare differently-shaped organisms - 1,000 Ám is 1mm.
Genome size in Mb (megabases or 1,000,000 nucleotide base pairs) - the human genome is 3000 Mb.
G + C is the percentage of nucleotides in the genome that are guanine or cytosine.

Only a tiny minority of the archaea, bacteria, fungi and animals that inhabit soil are known; a small selection of them is represented in the Top Trumps game. There are estimated to be at least 10,000 different species of bacteria in every gram of soil but only 1% of those can be grown in the lab.

Sequencing DNA from soil indicates the number of different groups when results are compared to a sequence database and allows us to estimate abundance even when we cannot isolate the organisms. However, most of the sequences appear to come from "unknown bacteria".

Although there are many invertebrates in soil, they do not make up a significant proportion of DNA extracted directly from the soil.

The abundance data refers to the group named on the top of the card but trophic group, sequence and cell size data refer to whichever species (or nearest categorization) is named in the text.