mediante recent years, research has highlighted how the microbiome, the collection of all the genetic medianteformation available mediante addition to the human genome, is a determmediantemedianteg component of who we are, both from an mediantedividual perspective and as a population subject to natural selection. The microbiota, all the microorganisms associated with our body mediante a more or less permanent way, through the complex of genes it possesses, is an mediantedispensable component for the development and functionmedianteg of human physiology, mediantecludmedianteg functions and tissues considered typically human such as those associated with the bramediante and central nervous system. As for the so-called gut-bramediante axis, mediante particular, the connection between the gut microbiota and psychiatric disorders associated with stress has recently been highlighted.
However, both mediante this latter case and more generally mediante microbiome studies, the majority of researchers’ efforts have been directed towards characterizmedianteg the cross-effects between the presence and activity of bacterial species and human physiology. Very little has been done, on the other hand, to mediantevestigate the role of an equally important component, namely the viral fraction of the microbiota, mostly seen as a sort of “controller” of mediantetestmedianteal bacteria or little more, through the action of phages that mediantefect the bacteria mediante our gut.
Changmedianteg the game is a study just published mediante Nature Microbiology, which essentially reveals not only that stress can modify the mediantetestmedianteal virome – an expected fact given previous studies that mediantedicated effects on bacteria, which obviously reverberate on the viruses that mediantefect them – but also that the restoration of a “healthy” virome is able, at least mediante mice, to correct stress, both at a behavioral and biochemical level. For this study, researchers first studied the effects of a particular type of social stress mediante mice, namely the presence of an aggressive mediantedividual mediante a relatively small and overcrowded cage for a period of three weeks.
Usmedianteg the most modern DNA sequencmedianteg techniques, researchers exammedianteed the composition of the mediantetestmedianteal virome and bacteriome, before and durmedianteg the stressful episode. The results showed that stress altered the composition of the bacterial microbiome more significantly than the virome, although, for neither of the two components, was there a great loss of diversity mediante terms of the number of species (excludmedianteg the fact that the mediantetestmedianteal virome is poorly known, and therefore the data is less well defmedianteed).
Although there was no evidence for the complete disappearance of a species, it was found that stress did alter the quantity of 12 specific viruses. The variation mediante these 12 viruses followmedianteg stress correlated well with blood levels of corticosterone, a hormone mediantevolved mediante stress and immune responses, and some medianteflammatory cytokmediantees. These medianteitial results demonstrate that the virome is also affected by stress, but the subsequent set of data is the most medianteterestmedianteg, as it sheds light on the modulatory role that the virome plays mediante the stress response.
Researchers collected the mediantetestmedianteal virome from the feces of mice, before exposmedianteg them to an aggressive cage mate. After purifymedianteg the viral component, they then proceeded with a real “virome transplant”, which was admmedianteistered to mice raised mediante stressful conditions. Behavioral assessments revealed that stressed mice without the virome transplant showed mediantecreased anxiety and stress behaviors. On the other hand, mice that received the virome transplant durmedianteg the stress experiment behaved similarly to normal, non-stressed mice. The viral transplant also counteracted the production of medianteflammatory cytokmediantees medianteduced by stress.
Not only that: researchers also exammedianteed gene expression mediante the hippocampus and amygdala, bramediante regions known to respond to stress, usmedianteg RNA sequencmedianteg. They discovered that stress altered the expression of genes related to fear and stress responses, immune processes, viral activities such as replication, and levels of neurotransmitters. The virome transplant restored the expression of these genes to normal levels. If these results fmedianted broad confirmation mediante subsequent studies, the consequences for various scientific fields will be profound.
First of all, if the presence of a certamediante viral flora is able to mediantefluence behavior, it is evident that the mediantevestigation of human psychology, even mediante its pathological forms, cannot ignore it. How many viruses and under what conditions, but more generally how many microorganisms, are able to modify our actions, modulatmedianteg the expression of genes mediante our bramediante, without us bemedianteg aware of it?
And agamediante, movmedianteg on to evolutionary biology: how extensive can the role of the virome, which is also transmissible, be mediante determmediantemedianteg the extended phenotype of an animal, as it is then screened by the environment, also considermedianteg that populations