{"id":1513,"date":"2022-05-20T18:24:22","date_gmt":"2022-05-20T18:24:22","guid":{"rendered":"https:\/\/www.vanderbilt.edu\/evolution\/?p=1513"},"modified":"2023-02-16T16:29:56","modified_gmt":"2023-02-16T16:29:56","slug":"1513-2","status":"publish","type":"post","link":"https:\/\/www.vanderbilt.edu\/evolution\/1513-2\/","title":{"rendered":"“The Hunger Games: E. coli edition” demonstrates how mutualism and cooperative behavior shape species"},"content":{"rendered":"

Andy Flick, Evolutionary Studies Initiative scientific coordinator<\/em><\/p>\n

Bacteria, not unlike humans, can take up more resources than necessary. When this happens, synthesized byproducts can leak into the environment. This allows the nearby bacteria to evolve cooperative behaviors, such as using the byproducts as nutrients. Cooperation in bacterial communities has also been previously observed with behaviors like altering the environment or forming new structures like biofilms.<\/p>\n

\u201cMaking your own resources costs energy. Bacteria can evolve to rely on each other\u2014and also conserve energy\u2014through mutations that result in the loss of certain metabolic processes that can be supplemented by using these now public goods,\u201d said Megan Behringer<\/a>, an assistant professor in biological sciences.<\/p>\n

\"Woman
Behringer inspects some petri dishes containing E. coli colonies with postdoctoral trainee, Sarah Worthan.<\/figcaption><\/figure>\n

Behringer, also a member of the Evolutionary Studies Initiative<\/a>, published the study, \u201cComplex Ecotype Dynamics Evolve in Response to Fluctuating Resources<\/a>\u201d in the journal mBio <\/em>on May 16. The study explores the effects of feast and famine cycles within groups of the intestine-dwelling bacteria E. coli<\/em>. The work was a collaborative effort between the Behringer lab and Wei-Chin Ho<\/a>, a postdoctoral researcher at Arizona State University.<\/p>\n

Behringer and Ho set out to test this cooperation in E. coli<\/em> under feast and famine conditions. They set up the bacteria with a broth medium to grow in. After 10 days, the bacteria were transferred to new broth medium. The bacteria used up most of the resources within the new broth after about one day.<\/p>\n

\u201cE. coli<\/em> grow very quickly and can exhaust their preferred nutrients within a day, so if we are transferring the cells every 10-days like in this experiment, they will spend the next 9 days scavenging for nutrients\u2014including cannibalizing other E. coli<\/em> that don\u2019t survive the harsh, nutrient limited conditions,\u201d Behringer said. \u201cIt\u2019s kind of cruel really, because for us researchers it feels like we are just mixing up tubes every 10-days, but the bacteria are participating in The Hunger Games<\/em>.\u201d<\/p>\n

Every 100 days for 900 days total, Behringer and Ho sequenced the bacterial genomes. Following nine genome sequencing timepoints, the researchers confirmed that though the bacteria started as a group of highly similar individuals, they quickly evolved into two specialized kinds, or ecotypes. One ecotype spent energy gathering iron from the environment but did not put much energy into producing fatty acids. The other ecotype did not gather iron efficiently but did well producing fatty acids.<\/p>\n

While we know that cooperative interactions occur in our guts and in the wild, we know less about how these interactions arise. To date, most of the study of cross-feeding in the lab has focused on microbes that have been engineered to cooperate or where the interaction has evolved in the lab, but it\u2019s one-sided (A feeds B but B doesn\u2019t feed A), Behringer said. In this study we found that through repeated cycles of feast and famine bacteria can evolve what appears to be bidirectional cross-feeding (A feeds B and B feeds A).<\/p>\n

This is exciting because until now evolution has trouble explaining this type of efficient cooperation. Feast and famine are very natural fluctuations for bacteria. Even in our guts\u2014an environment thought of as nutrient rich\u2014bacteria can still be constrained for certain resources, like nitrogen. The study\u2019s results suggest that these feast and famine dynamics can provide the conditions for bacteria to evolve these cooperative cross-feeding behaviors and provide insight into how the bacterial communities that reside in our guts, with our crops, in lakes and streams and beyond become so complex.<\/p>\n

\u201cOur results highlight mutualistic behaviors and populational structures can emerge even within a single species,\u201d Ho said. \u201cThe results from our experiment will serve as a good model for the evolutionary study of mutualism.\u201d In biology, mutualism acknowledges the interaction between at least two species, where each contributes to a net benefit for the interacting species.<\/p>\n

\u201cWe further hypothesized that the bacteria were evolving to become more efficient by sharing the burden of performing these functions which would be beneficial in starvation conditions,\u201d Behringer said. \u201cBacteria are often faced with cycles of feast and famine in nature. The evolution we observed in this experiment in the lab may be similar to how these cooperative behaviors evolve in wild microbial populations.\u201d<\/p>\n

The next step is to investigate these behaviors at a finer scale. The group knows what happens after every 100 days, and they have frozen bacteria from every 30 days through the experiment, a window into what is happening before the bacteria evolve into two distinct ecotypes. They also plan to look for cheaters; organisms that use the byproducts of other bacteria but do not produce any on their own.<\/p>\n

This work was supported by Army Research Office grants W911NF-14-1-0411 and W911NF-21-1-0161 and National Institutes of Health grants F32GM123703 and R35GM122566.<\/p>\n

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Andy Flick, Evolutionary Studies Initiative scientific coordinator Bacteria, not unlike humans, can take up more resources than necessary. When this happens, synthesized byproducts can leak into the environment. This allows the nearby bacteria to evolve cooperative behaviors, such as using the byproducts as nutrients. Cooperation in bacterial communities has also been previously observed with behaviors…<\/p>\n","protected":false},"author":2421,"featured_media":1505,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true},"categories":[1],"tags":[37,13,14,16,36,15,35,34,38],"acf":[],"yoast_head":"\n\n\n\n\n\n\n\n\n\n\n\n\t\n\t\n\t\n\n\n\t\n\t\n\t\n