CrAssphange viruses reach the third part of the world countries and vary by geographical areas

CrAssphange viruses –fags infecting bacteria in the human intestine tract first described in 2014- are distributed around the third part of all the countries in the world and vary by geographical areas, according to a study published in the journal Nature Microbiology in which researchers Maite Muniesa, Joan Jofre and Cristina Garcia-Aljaro, from the Research Group on Health related Water Microbiology (MARS) of the Faculty of Biology of the University of Barcelona –have taken part.

This group of viruses –one of the most prevailing groups in the world population- has evolved during millions of years over the evolutionary lineage of the human species, stresses the international study led by expert Rob Edwards from the San Diego State University (United States).

The new study analyses the presence of crAssphange fags in human faecal samples, waste waters and metagenomes from intestinal microbiota in adults and children worldwide. A total of a hundred and fifteen researchers from sixty-five countries, among which are experts from the UB, UAB and the University of Alicante. “We are in debt to all the amazing colleagues around the world who helped us explore the global diversity of this unique virus. This is truly a world-first in the global scope and nature of the project”, notes researcher Rob Edwards.

Hidden viruses identified with metagenomics

CrAssphage viruses infect some species of the genera Bacteroides, anaerobic bacteria present in the microbiota o the digestive tract in humans and other organisms. Despite their worldwide distribution, these fags were just discovered in 2014.

“CrAssphage are not virus we can freely isolate and do not generate lysis dapples when grown in Petri plaques in the laboratory. Therefore, these were detected in 2014 with metagenomic techniques”, notes the lecturer Maite Muniesa, from the Department of Genetics, Microbiology and Statistics of the UB.

The new study reveals these are viruses from the Podoviridae family (short-tail fag) with a dual chain DNA genome, and a relatively large size (100 kb). The genome of the viruses is quite similar between the different human groups, with small sequencing variations depending on the geographical field. This degree of conservation of the viral genome could be explained by the environmental traits of the intestinal tract, an atmosphere with relatively stable conditions for the viruses over their evolution.

“This singularity is quite exceptional if regarding the high rates of virus mutations and the ‘mosaicism’ concept applicable to the genome of many viruses”, note the UB authors.

CrAssphage virus: the first universal indicator of human fecal contamination

The new study lists the group of crAssphage viruses of human fecal microbiomes in four sub-families with ten genera. There is a case of a same individual who was detected seven different crAssphage viruses.

These viruses, in addition, could be the first indicators of human fecal contamination worldwide, note the authors. Therefore, the group of bacteriophages could respond to the scientific challenge of finding indicators of human fecal contamination at a global geographical scale and not only regional scale.

A shared evolution with the hominid lineage

Researchers do not know the biological role pf the crAssphage virus in the human intestinal microbiota, nor how it interacts with its bacterial hosts. However, the high prevalence of the virus in the human population could indicate the existence of an inter-relation with mutual benefits. ““CrAssphage does not seem to have any direct benefit, for example to our health. But we found closely related viruses in fecal samples from gorillas, monkeys, and other wild primates.”, notes Bas Dutilh”, expert from Utrecht University (the Netherlands) and co-leader of the study.

“Based on these results, - continues Dutilh- we think that it has evolved with us for millions of years, and spread with humans across the globe. This is the first time anyone has shown that human gut viruses can be at least as old as the human lineage”.

Maite Muniesa says that “we seem to be facing a common symbiont in our intestine, which is not affected by changes in age –it is abundant in children- nor changes in diet. Its geographical expansion is the result of human migratory movements around the planet”.

The Research Group on Health related Microbiology Waters (MARS) of the UB is a leading team in the description and characterization of bacteriophages that infect Bacteroides as indicators of human fecal contamination in the environment. As part of the study, the scientific contribution of the UB experts –where the experimental task by lecturer Cristina Garcia-Aljaro is outstanding- has been mainly focused on the characterization of samples from waste waters in Catalonia and the sequencing of several genomic regions pf crAssphange.

“In this global study, the application of multiple analysis tools of metagenomics data enabled detecting this virus in several samples and creating global phylogenetic trees and data clusters with the obtained metadata”, conclude Maite Muniesa, Joan Jofre and Cristina Garcia-Aljaro.