MSU researchers have spotted significant differences in genetic libraries among thought-to-be similar bacteria strains. The results, published this week in the journal the Proceedings of the National Academy of Sciences, suggest that new definitions are needed to catalogue bacteria single-celled organisms with at least a 3.5 billion-year history.
"It's important to point out the importance of these small microbes on Earth; even though they are small, their mass in soil and water is equal to that of all plants," said MSU microbiologist James Tiedje, one of the study's authors. "Furthermore, they are responsible for recycling the key elements of life so life on Earth can continue."
DNA, used by all life including bacteria to store genetic information, is a double-stranded molecule. When a given DNA molecule is split in two, for instance by heating it up, its two strands will spontaneously find each other, or reassociate, when the temperature drops.
Scientists have long exploited this fact in their rough rule-of-thumb approach for saying just what makes up a species of bacteria. Single strands of DNA from two bacteria are mixed together. If most of these strands reassociate specifically, if 70 percent of strands from bacteria A come together with strands from bacteria B then the two bacteria strains are said to members of the same species.
Tiedje and his MSU colleague, microbiologist Konstantinos Konstantinidis, set out to put this mix and match approach to the test. The two scientists selected 70 related bacteria whose genomes, or complete genetic libraries, had been fully sequenced.