Specially¹ designed probiotics（益生菌） can modulate² the physiology³（生理学） of host fat cells say scientists writing in Microbiology. The findings could lead to specialised probiotics that have a role in the prevention or treatment of conditions such as obesity⁴. Scientists from the Alimentary⁵ Pharmabiotic Centre (APC), Cork⁶, University College Cork and Teagasc, in Ireland engineered a strain of Lactobacillus to produce a version of a molecule⁷ called conjugated⁸ linoleic acid (CLA共轭亚麻油酸). When this engineered bacterial⁹ strain was fed to mice, the researchers found that the composition of the mice's fat tissue was significantly altered, demonstrating that ingesting live bacteria can influence metabolism¹⁰ at remote sites in the body.

CLA is a fatty acid that is produced in different versions by different bacteria. One type, called t10, c12 CLA, has been shown to be associated with decreased body fat in humans and other animals. t10, c12 CLA also has the ability to inhibit¹¹ the growth of colon¹² cancer cells and induce their death. However, this type of CLA is only produced by certain types of bacteria including Propionibacterium acnes – a skin bacterium¹³ that can cause acne（痤疮，粉刺） .

In this study, an enzyme-encoding gene¹⁴ from P. acnes was transferred to the Lactobacillus strain allowing it to produce t10, c12 CLA. Lactobacillus strains are common inhabitants of the normal gut¹⁵ flora¹⁶（植物群） and are often found in probiotic products. The researchers found that the level of t10, c12 CLA in the mice's fat tissue quadrupled when they were fed this recombinant probiotic. Thus, this study demonstrates that gut microbes have an impact on host metabolism, and in particular fat composition.

Dr Catherine Stanton, from Teagasc who led the study explained the significance of the results. "CLA has already been shown to alleviate¹⁷（减轻，缓和） non-alcoholic fatty liver disease that often accompanies obesity. Therefore, increasing levels of CLA in the liver by ingestion（摄取，吸收） of a probiotic strain is of therapeutic¹⁸ relevance," she said. "Furthermore, fat is not an inert¹⁹ layer around our bodies, it is active and proinflammatory（促炎的） and is a risk factor for many diseases, including cancers. The work shows that there is potential to influence this through diet-microbe-host interactions in the gut."

The same group of researchers previously²⁰ found that microbially produced CLA was able to reduce the viability²¹ of colon cancer cells by 92%. "It is possible that a CLA-producing probiotic may also be able to keep colon cancer cells in check. All our findings to date demonstrate that the metabolism of gut bacteria can modulate host cell activity in ways that are beneficial to the host," explained Dr Stanton. "We need to further investigate the effects of CLA-producing bacteria on human metabolism, but our work so far certainly opens up new possibilities for the use of probiotics for improvement of human health."