New findings show how bacteria undergo genome evolution

Scientists at the Institut Pasteur and the University of Maryland have revealed how bacterial and archaea microbes successfully evolve their gene repertoires to face new challenges, predominantly by acquiring genes from other individuals. The study, published in the open-access journal PLoS Genetics on January 27, was instigated to clarify the role of gene duplication, an important source of novelty in multicellular organisms, in bacteria. Microbes live and thrive in incredibly diverse and harsh conditions, from boiling or freezing water to the human immune system. This remarkable adaptability results from their ability to quickly modify their repertoire of protein functions by gaining, losing and modifying their genes. Microbes were known to modify genes to expand their repertoire of protein families in two ways: via duplication processes followed by slow functional specialization, in the same way as large multicellular organisms like us, and by acquiring different genes directly from other microbes. The latter process, known as horizontal gene transfer (HGT), is notoriously conspicuous in the spread of antibiotic resistance, turning some bacteria into drug-resistant 'superbugs' such as MRSA (methocillin-resistant Staphylococcus aureus), a serious public health concern.

The researchers examined a large database of microbial genomes, including some of the most virulent human pathogens, to discover whether duplication or HGT was the most common expansion method. They show that gene family expansion can indeed follow both routes, but unlike large multicellular organisms, it predominantly takes place by horizontal transfer. Thus, quick diversification of microbial functions results from the recruitment by microbes of pre-existing adaptations from other microbes.

The study concludes with the observation that, since microbes invented the majority of life's biochemical diversity, from respiration to photosynthesis, we must recognize the predominant role of HGT in the diversification of all protein families.

Source: Public Library of Science