It's generally understood how genetic information is spread: from an organism to its offspring. For this reason, the traditional representation of evolution and the relationship between organisms is portrayed as a "tree," with an increasing number of branches emanating from the origin. But it turns out that this well-understood structure doesn't apply to microbes.
Bacteria don't just transmit genetic information to their offspring, they also exchange genes with other bacteria -- even bacteria from different species. This "horizontal gene transfer" happens with great regularity, and is responsible for a nearly 10% of the "gene transfer events" in bacterial evolution. As a result, the relationship between different microbial species is closer to a network than a tree, with otherwise distant types connected through gene swapping. Now researchers at the European Bioinformatics Institute (EBI) have determined what that bacterial network looks like -- and it turns out that the bacterial horizontal gene transfer network (PDF) has a lot in common with the world wide web.
This network appears to behave in a 'scale-free' manner. This term was first coined by physicist Albert-Laszlo Barabasi and his colleagues at the University of Notre Dame, Indiana, in the US. In 1998, they mapped the connectedness of the World Wide Web and found, to their surprise, that the web did not have an even distribution of connectivity (so-called 'random connectivity') but instead, a very few network nodes (called 'hubs') were far more connected than other nodes.One property of scale-free networks is their 'small-world' nature: travelling from one node to any other is very fast. Other well-known examples of small-world networks include social networks and air-travel connections.
These characteristics allow the hubs to serve as bacterial 'gene banks', providing a medium to acquire and redistribute genes in microbial communities.
So what does this mean? The biggest implication concerns evolved resistance to antibiotics. Because of the horizontal gene transfer, a resistance that evolved naturally in one species can be transferred by chance, fully formed, to another bacterial species.
According to Christos Ouzounis, this pattern has important implications for the understanding of horizontal gene transfer because, in small-world networks, the shortest path between any two network nodes is relatively small. In other words, 'a gene can rapidly be disseminated from organism to organism through very few horizontal gene transfer events', explains the scientist. [...]'It's entirely possible that apparently harmless organisms are quietly spreading antibiotic resistance under our feet,' concludes Christos Ouzounis.
Unstated in the article, but implied by this analysis, is that thinking of bacterial relationships as a scale-free network could lead to new approaches to the control of antibiotic resistance, and possibly even to new types of anti-bacterial treatments; it also means that novel antibiotics may have greater-than-anticipated effects on seemingly unrelated bacteria (most of which are quite helpful and important to ecological processes).
In addition -- and this is informed conjecture on my part -- this discovery could lead to new insights into how information networks can, in turn, evolve resistances to external attacks (such as spam, viruses and "denial of service" episodes).
Comments (6)
Just maybe we could look at probiotics to compliment our indiscriminate use of antibiotics. Body Ecology Diet helps many reculture their guts, sauerkraut, kefir. Soil Foodweb includes the huge importance of bacteria and fungi in restoration and getting agribusiness off chemical addiction and organic growers off too many 'natural' imports and imputs. We need to become more than aware of our symbiosis, out on that limb as we are, sawing, sawing, never seeing. We need to rethink disease in light of respect for what life does to change itself by fever and infection. We can have more gut level thought, less abstraction and understand how the nets and webs work without having to go into overdrive with coffee, leaving our adrenals ruined and exhausted.
Posted by Kim McDodge | July 11, 2005 6:41 PM
Posted on July 11, 2005 18:41
Biological networks should be analysed according to the laws of Quantum mechanics and Quantum neurology and Quantum Genomics (See Penrose).
Microtubules and Nanotubes are the atoms (nodes) of the DNA and the Neuron.
Posted by asher Idan | July 11, 2005 10:53 PM
Posted on July 11, 2005 22:53
further, as the fringe biologists are trying to communicate, bacteria spill their guts in a truly global fashion and in evolution they formed symbiotic partnerships that provided the building blocks of more complex organisms and so the roles of RNA & DNA evolved. Now we are confidently tinkering with DNA & refusing to acknowldge the complex influences and potential spillages in areas we understand so poorly.
Posted by Janelle | July 13, 2005 3:32 AM
Posted on July 13, 2005 03:32
I recommend the book "Symbiosis" by Lynn Margulis. Brilliant, and hardly fringe.
Posted by David Foley | July 13, 2005 5:25 AM
Posted on July 13, 2005 05:25
yeh, changed my point a bit & spied that word fringe too late as I hit post. David, re: this & dawkins post: thanks & all recommendations welomed! I find that Elisabeth Sahtouris has a knack for communicating these issues with clarity, wonderful metaphors & hope. eg on big picture TV
Posted by Janelle | July 13, 2005 9:06 AM
Posted on July 13, 2005 09:06
I recommend the book "Global Brain" by Howard Bloom. It ranges much farther afield than a discussion of bacteria, but it certainly gives them a fascinating treatment, describing the global networks of DNA-swapping bacteria as a mass mind comparable to, and even much more capable than, human society.
Posted by Lawrence Wang | July 13, 2005 10:15 AM
Posted on July 13, 2005 10:15