Scientists characterize previously unknown intestinal reactions.
Strictly speaking, humans cannot digest complex carbohydrates – that is the job of bacteria in our large intestine. UC Riverside scientists have just discovered a new group of viruses that attack these bacteria.
The viruses and the ways in which they evade counterattacks from their bacterial hosts are described in an article published in Cell Reports.
Bacterioids can make up as much as 60% of all bacteria living in a human’s colon and are an important way people get energy. Without them, we would have difficulty digesting bread, beans, vegetables, or other favorite foods. Given their importance, it is surprising that scientists know so little about viruses that attack Bacteroides.
“This is a largely unexplored area,” said microbiologist Patrick Degnan, an assistant professor of microbiology and plant pathology who led the research.
To find a virus that attacks Bacteroides, Degnan and his team analyzed a collection of bacterial genomes in which viruses can hide for several generations until something triggers them to replicate, attack, and leave their host. This viral lifestyle is not without risk, as mutations can appear over time that prevent the virus from escaping its host.
When analyzing the genome of Bacteroides vulgatus, Degnan’s team found out DNA Belonging to a virus called BV01. However, it turned out to be difficult to determine if the virus was able to escape its host or re-infect it.
Reconstructed microscope image of a bacteriophage, which is a virus that attacks bacteria. Photo credit: Purdue University and Seyet LLC
“We tried every trick we could think of. Nothing worked in the lab until we worked with an aseptic mouse model, ”said Degnan. “Then the virus jumped.”
This was possible due to Degnan’s collaboration with UCR colleague, co-author and fellow microbiologist Ansel Hsiao.
This result suggests that conditions in the mammalian gut act as triggers for BV01 activity. The finding underscores the importance of in vitro and in vivo experiments for understanding the biology of microbes.
Looking for more information on the indirect effects of this bacterial virus on humans, Degnan’s team found that when BV01 infects a host cell, it interferes with that cell’s normal behavior.
“Over 100 genes change the way they are expressed after infection,” said Degnan.
Two of the altered genes that the researchers noticed are both responsible for deactivating bile acids, which are toxic to microbes. The authors speculate that this may alter the bacteria ‘s sensitivity to bile acids, but it also affects the bacteria’ s ability to become infected with other viruses.
“This virus can change the metabolism of these bacteria in the human gut that are so important to our own metabolism,” said Degnan.
Although the full extent of BV01 infection is not yet known, scientists believe that viruses that alter the frequency and activity of gut bacteria contribute to human health and disease. One area for future study will be the effect of diet on BV01 and similar viruses, as certain foods can cause our bodies to release more bile.
Degnan also notes that BV01 is just one of a group of viruses that his team has similarly identified. The Salyersviridae group is named after the famous microbiologist Abigail Salyers, whose work on gut bacteria advanced the science of antibiotic resistance.
Further research is planned to understand the biology of these viruses.
“It was in sight, but no one has characterized this important group of viruses that affect what has been in our stomachs so far,” said Degnan.
Reference: “Infection with Bacteroides Phage BV01 alters the host transcriptome and bile acid metabolism in a common human gut microbe” by Danielle E. Campbell, Lindsey K. Ly and Jason M. R, September 15, 2020, Cell Reports.
DOI: 10.1016 / j.celrep.2020.108142
