Viruses worldwide battled by gut microbes

The human gut is a comprehensive ecosystem of microbes and plays a vital role in the body's wellbeing and defense against disease, as the gut microbiota constantly have to fight attacks from viruses. A study featured online in Genome Research reports that researchers have identified a common set of viruses that is linked to gut microbiota in individuals worldwide when they analyzed the bacterial immune system. Phages, i.e. viruses that live off bacteria represent a constant threat to the health of bacterial communities with viruses outnumbering bacterial cells ten to one in many ecological systems. Considering the number of bacteria within the human gut, scientists also discovered a high prevalence of phages, which raised the questions of how viruses can be identified that target gut microbiota, and what is the difference in viral communities between individuals and global populations, as well as what can be learned from this with regard to human health and disease? Israeli researchers decided to use coded information from a bacterial immune system to get to the bottom of these questions. They discovered a process, which is similar to the way in which antibodies are used by the human immune system, i.e. bacteria 'steal' tiny pieces of DNA from the attacking phages, which are stored in the bacterial genome CRISPR loci (clustered regularly interspaced short palindromic repeats) and then used to identify and respond to the attacker. Senior author, Rotem Sorek from the Weizmann Institute of Science said: "In our study we searched for such stolen phage DNA pieces carried by bacteria living in the human gut. We then used these pieces to identify DNA of phages that co-exist with the bacteria in the gut." The team applied this method to identify and evaluate phages in European individual's gut microbiota, discovering that almost 80% of phages are shared between two or more individuals. They then compared their data to samples they took previously from American and Japanese individuals and to their surprise, they also discovered phages that exist in their European data set. According to Sorek, this means that people's gut microbiota are repeatedly infected with hundreds of virus' types. "These viruses can kill some of our gut bacteria. It is therefore likely that these viruses can influence human health," he said. The researchers highlight that it is of key importance to gain a better understanding of the amount of pressure that is placed on the 'good' bacteria, which is crucial to maintain healthy, as evidence is mounting regarding the bacteria's beneficial roles in the healthy human gut. They state: "Our discovery of a large set of phages attacking these good bacteria in our gut opens a window for understanding how they affect human health." Scientists are now able to investigate how phage functions in the gut change over time and what impact this may have on diseases like inflammatory bowel disease, as well as finding more effective methods to treat these diseases.