This month’s 5-minute microbiome science roundup includes some important papers published this month related to both health and disease. The two colorectal cancer microbiome-related papers published in Nature are a sign that the field is beginning to mature, as metagenomics datasets on a single disease can be pooled for broader insights.
Meta-analysis of fecal metagenomes reveals global microbial signatures that are specific for colorectal cancer + Metagenomic analysis of colorectal cancer datasets identifies cross-cohort microbial diagnostic signatures and a link with choline degradation
Several research groups have used shotgun metagenomics to look for gut microbial signatures of colorectal cancer (CRC), but these signatures tended to vary from study to study. Now, the field is advanced enough to be able to combine datasets from multiple shotgun metagenomics studies in order to identify microbiome signatures that are broadly applicable across populations. A pair of papers in Nature this month pooled CRC datasets and found 29 species that appeared to mark the disease; they also found (somewhat surprisingly) higher gut microbiome richness in those with CRC, as well as altered potential for the microbiome to metabolize the essential nutrient choline. Note that these findings don’t mean the identified bacteria cause colorectal cancer – but there may be some diagnostic application for the findings.
So few papers are available describing the effects of probiotic strains on healthy people: some studies have shown prevention of sickness over a longer term with probiotic administration, but what about immediate effects on generally healthy individuals? A new study used MEG to test the effects of social stress (i.e. the perception of being ostracized or excluded in a computer game) on healthy people who either had or had not consumed doses of the probiotic Bifidobacterium longum1714™ for 4 weeks. In the probiotic group, experimenters saw altered resting-state brain activity and altered brain responses during the stressful task.
When it comes to bacteria, the concept of ‘natural selection’ is well known: bugs adapt to a changing environment. But how does this apply to commensal bacteria in the human gut? A study focusing on Bacteroides fragilisin the healthy human gut found its bacterialgenes changed constantly according to different within-personconditions. It’s possible that these multiple adaptations in a single individual’s gut are what allow the bacteria to colonize in the long term.
In a very impressive research feat, a group of researchers tested healthy women and infants at 11 sites around the world: two in Ethiopia, two in The Gambia, two in the US, and one site each in Ghana, Kenya, Peru, Spain, and Sweden. First, they found the microbes in breastmilk and infant stool varied widely at the different sites. And second, when they looked for similarities between a mother’s breast milk and her infant’s stool, they found that the specific bacterial taxa didn’t always translate directly—even though at the community level, the complex microbiomes in breastmilk and infant stool were positively associated with each other.
Afew examples are emerging in the literature of metabolites that gut microbes produce (or help produce), which end up contributing to disease. A new suite of data from Japanese scientists highlights a host/microbial co-metabolite called phenyl sulfate (PS), which is produced from dietary components being metabolized by both the gut microbiota and liver. The researchers found evidence from both rodents and humans that PS is implicated in albuminuria (that is, the appearance of the protein albumin in the urine), and thus may signal the worsening of diabetic kidney disease.