"In fact, because there are alternative pathways to the same product, by removing either of the genes you make the other essential for survival; each gene deletion reduces the available space for further reduction of the genome.
"Including these alternative pathways into the minimal genome almost doubles its size."
The researchers have developed a way of predicting bacterial genome content using two bacteria that have evolved from E.coli.
Buchnera and Wigglesworthia live inside insects in a symbiotic relationship where they provide essential molecules for their hosts in return for essential basic foods.
Since evolving from E.coli, the Buchnera and Wigglesworthia genomes have lost some of the genes that they would otherwise need for survival.
Using computer modelling and knowledge of the present day ecology of the bacteria the researchers were able to model this process of gene loss.
They accurately predicted about 80 per cent of the gene content of the two bacteria, including some of the non-obvious features of their genomes.
"Far from being a cause for disease, the insects need these bacteria to supply them with essential nutrients," said Professor Hurst.
"In these relatively cosy conditions, Buchnera and Wigglesworthia have lost some of the genes they would otherwise need to produce some of the basic molecules they need to survive.
"Being able to predict the content of a genome based on the ecology of an organism is useful because we could potentially use it to predict gene content at different stages of an organism's evolution.
"This will help us understand more about how the genome of different organisms have evolved over long periods of time and should also inform attempts by experimentalists to construct minimal genomes by gradual evolution in the laboratory."
Similar methods might also be used to build a blueprint of a bacterium with desired metabolic pro
Source:University of Bath