Gut bacteria, glycerol and a cooked-meat carcinogen
What it found
In lab tests, certain gut bacteria worked together to turn a liver-made form of the cooked-meat chemical PhIP into a compound with lower mutagenic potential.
The same bacterial genes were less common in the gut bacteria of people with colorectal cancer.
What they found
Studies in people
Genes in healthy and CRC guts
All 156 stool metagenomes tested carried b-gus and gdh genes. The average gene abundance of b-gus and gdh did not differ between healthy people and people with colorectal cancer.
Bacterial groups differ
In people with colorectal cancer, the share of gdh genes from bacteria confirmed to transform PhIP (E. hallii, F. plautii, B. obeum and L. reuteri) was lower than in healthy people. The proportions of b-gus genes from Firmicutes and Bacteroidetes also differed between the two groups.
Animal and lab studies
Two-step bacterial conversion
In lab cultures, Faecalibacterium prausnitzii used beta-glucuronidase to release PhIP from PhIP-G. Then Flavonifractor plautii, Blautia obeum, Eubacterium hallii and Lactobacillus reuteri used glycerol/diol dehydratase to convert PhIP to PhIP-M1.
Working together
When F. prausnitzii was grown together with F. plautii or L. reuteri, up to about one third of the PhIP-G was converted all the way to PhIP-M1. In these co-cultures, roughly half of the PhIP-G was turned into PhIP and about 30% into PhIP-M1.
Glycerol helps
PhIP-M1 formation rose in a straight line with glycerol use up to 14 mM in the lab cultures, then levelled off. PhIP-G breakdown also rose with beta-glucuronidase activity and levelled off at about 1.0 U per mg protein.
What the authors conclude
“These results are the first observation that the bacterial B-GUS and GDH cooperatively mediate the stepwise conversion of HCA-G to HCA-M1 via intermediate HCA, and provide potential targets to modulate gut microbial activities for mitigating the risk of HCA carcinogenesis.”
Also in their conclusions
- They say this is the first demonstration that gut microbes mediate the stepwise transformation of PhIP-G to PhIP-M1 via the intermediate production of PhIP.
- They suggest that targeted manipulation of gut microbes with specific functions, or dietary glycerol supplementation, might modify gut microbial activity to reduce HCA-induced colorectal cancer risk.
- They call for further investigations to evaluate how bacterial reactions of PhIP-G and PhIP impact health, particularly considering the intermediacy of acrolein in this process.
How it was done
Eating red and processed meat has been linked to a higher risk of colorectal cancer, partly through heterocyclic amines (HCA) formed when meat is cooked. The authors wanted to know whether gut bacteria can transform HCA-glucuronides, the main form of these chemicals reaching the colon, into less harmful compounds.
They grew single strains and pairs of human gut bacteria in the lab with PhIP-G, a liver metabolite of the cooked-meat chemical PhIP, plus glycerol. They also screened stool metagenomes from 103 healthy people and 53 people with colorectal cancer for the bacterial genes beta-glucuronidase (b-gus) and glycerol/diol dehydratase (gdh).
What it can’t tell you
- These are lab experiments with bacterial cultures and a look at bacterial genes in stool samples. They cannot show what actually happens inside the human gut or whether this changes cancer risk in people.
- The metagenome screen only looked at which genes were present. It did not measure whether those genes were active or how much of these bacterial activities were happening in the gut.
Who paid
- Conflicts
- The authors declare that they have no competing interests.
- Authors work at
- Massachusetts Institute of Technology, USA
The paper
- Title
- Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation
- Type
- Study
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Zhang J, Lacroix C, Wortmann E, et al (2019). Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation. BMC microbiology. doi:10.1186/s12866-019-1483-xFree full textPubMed 31096909DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error