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 Gut Microbiome Speedometers ( BioTechniques Newsletter _ 2015 9 ) 
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 Gut Microbiome Speedometers 
 S . C . P . Williams 09 / 21 / 2015 
 BioTechniques Newsletter ( http : / / www . biotechniques . com / news / ) 
 A new method can detect the growth rates of gut bacteria using a single metagenomics sample , allowing researchers to show that growth rates are even better predictors of disease than bacterial abundance . .. 
 By comparing the abundance of different fragments of DNA in a metagenomics sample , researchers have discovered a new way to calculate the growth rate of any given bacterial species . Moreover , they ’ ve shown that the growth rate of species in the gut microbiome — not just the species ’ prevalence — is correlated with disease conditions , including diabetes and inflammatory bowel disease . 
 “ I think having another lens through which we can focus and look at metagenomics samples , beyond just their composition , is going to be very beneficial , ” said Eran Segal of the Weizmann Institute , one of the senior authors of the new study published in Science . While mapping genes from metagenomics samples , Segal and his colleagues noticed a sinusoidal shape in prevalence patterns of genes in some organisms . The pattern , they realized , reflected replicating DNA , with the peak of the curve — where gene material was most prevalent — representing the origin of replication for the bacterial genome . 
 The researchers then determined that the origin of replication — previously unknown for some species — wasn ’ t the only information they could get out of these prevalence curves . By calculating the ratio of the peak of the curve to the tail ends , they could determine the exact growth rate of the bacterial strain at the time the single metagenomic snapshot was taken . “ The ratio of the peak and the terminus really varied between people , so that was an indication that the same bacteria might be growing at different rates between people , ” said Segal . Indeed , when his group looked more closely at the growth rates , they found that they differed in people with diabetes or inflammatory bowel disease , and changed in mice after doses of antibiotics . 
 “ What was interesting for these bacteria was that prevalence wasn ’ t associated with the disease phenotype , but the growth rate was , ” said Segal . Why isn ’ t the growth rate simply reflected in the abundance of a species ? Some bacteria may be growing fast but are outcompeted by another bacteria growing even faster , Segal point out . And other bacteria may be dying . 
 Segal and his colleagues created software for calculating growth rates and made it available online for other researchers . They are planning to use it to follow up on the utility of growth rate as a diagnostic or prognostic tool in clinical settings . 
 Korem et al . 2015 . Growth dynamics of gut microbiota in health and disease inferred from single metagenomics sample . Science doi : 10 . 1126 / science . aac 4812