Going with the gut: Searching for cancer-fighting breakthroughs in gut bacteria

Recent research suggests that the human gut microbiome is crucial to providing protection against pathogens and maintaining the metabolic health of an individual. However, little is understood about the majority of species present in the gut microbiome and their specific role in the breakdown of indigestible food residues. The experiments focused on four novel strains of bacteria that were isolated from human fecal samples and investigated their metabolic capability to digest aromatic glycosides, a class of molecules containing a sugar bound to an aromatic ring. Activated aromatic glycosides derived from food have been implicated in preventing colon cancer cell growth; evidence indicates that the activity of microbes in the intestinal tract is activating these aromatic compounds.

The hypothesis being tested was that gut microbes could hydrolyze aromatic glycosides, releasing aromatic moieties that could potentially act against colon cancer. Initial characterization and 16S ribosomal RNA gene sequencing revealed that the fecal isolates were strains of a new bacterial species, most closely related to Clostridium citroniae, Desulfotomaculum guttoideum, and Clostridium xylanolyticum. These microbes are members of the Lachnospiraceae family, frequently reported in literature as active members of healthy gut microbiomes. Growth of the isolates was measured under anaerobic conditions in a minimal medium containing an aromatic compound as growth substrate.

The substrates tested were salicin, arbutin, rutin, and rebaudioside A; the latter two substrates are derivatives of aromatic glycosides. Growth was monitored by measuring the turbidity of cultures as OD660 values using spectrophotometry. Products resulting from breakdown and fermentation of the substrate were identified using high-pressure liquid chromatography (HPLC). Growth measurements and HPLC analyses showed that the isolates were able to use salicin and arbutin as growth substrates, yielding fermentation products. Rebaudioside A was not metabolized; the data on growth on rutin were insufficient to draw conclusions. Results of this study indicated that the isolates had the metabolic capability to cleave aromatic glycosides and ferment the sugar products.