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Saturday, July 23, 2011

Living in symbiosis

Anyone who's ever managed a multi-person project - or managed a kids' art project, for that matter - knows how hard it is to keep everyone working together in harmony. In the best case scenario, everyone's efforts benefit everyone else. But more likely, something will offset the balance and leave at least one person feeling alienated and bitter.

Maybe we should take a lesson from our microbes: in the majority of cases, the intestinal bacteria manage to exist in a nice symbiotic relationship with the human body that houses them. It can't be an easy task for all those cells (and we're talking trillions of bacterial cells) to operate in such close contact with their (comparatively) giant host. Yet they do - their project of "living in symbiosis" usually goes off without a hitch.

"Symbiosis". Photobucket image by GlynGPKSS 

How do the microbes achieve that symbiosis so successfully?

This was the question explored by a team of Harvard researchers under the direction of Dr. Wendy Garrett, an immunology professor and oncologist. Their 2011 paper is entitled Host and gut microbiota symbiotic factors: lessons from inflammatory bowel disease and successful symbionts.

The researchers at the Garrett lab happen to know a lot about Inflammatory Bowel Diseases (IBDs) possible examples of what can happen when a host and its bacteria fail to maintain symbiosis. So, more than anyone, these researchers know about the challenges faced by the host-bacteria relationship: the foods that enter the body (since fried beef takes a different toll on the microbes than lentil soup), the functioning of the immune system, and the number of pathogenic bacteria that are competing for space in the gut. All these things have the capacity to work against symbiosis.

The study reads like one of those workplace "let's identify our strengths" exercises. First, it explored what features of the host (i.e. the human body) contribute to symbiosis. Then, it covered the contributions of the bacteria themselves.

When it came to the body, the researchers picked out several genes that they felt were necessary for coexistence with gut bacteria. According to previous experiments, these genes affect the immune system and thus affect what bacteria colonize the gut. Meanwhile, the researchers identified three genera of bacteria that seemed especially good at living in symbiosis: Bacteroides, Helicobacter and Lactobacillus. The bacteria's list of workplace strengths included the ability to stick to mucosal surfaces inside the intestine, a tolerance for extreme pH shifts in the gut, and a propensity for lowering inflammatory processes in the body.

This makes for a nice, tidy presentation of what it takes to live in symbiosis: the right genes and the right environment. Possessing certain genes may make it easier for bacteria to get along with you. And the specific bacteria that you have encountered in your daily comings and goings may do their part to keep the relationship in harmony.

This is part of an exciting new research path - and it's about more than just IBD prevention. The Garrett lab is exploring the overall relationship between gut bacteria and the immune system - how disruptions in the community of gut bacteria may contribute to the body's inflammation responses, and how that inflammation might lead to disease or cancer.
Ballal SA, Gallini CA, Segata N, Huttenhower C, & Garrett WS (2011). Host and gut microbiota symbiotic factors: lessons from inflammatory bowel disease and successful symbionts. Cellular microbiology, 13 (4), 508-17 PMID: 21314883

1 comment:

  1. Hi
    I just found your blog today and am impressed with the simplicity that you have explaining complex topics. Will be looking forward to reading your future posts. Thanks so much!