Back in 2001, I proposed that the original cells, used to seed this planet, contained the ability to form “viretes.” The basic idea is that the virete would function something like a gamete, but instead of transmitting genetic information across time to future generations, it would transmit genetic information across space to facilitate the survival of the founding group (see my discussion on cross-talk ) by connecting them. Here is how I put it back in 2001:
Actually, I have been toying with the idea that viruses were designed (keeping in mind that I view viruses as non-living, life-dependent phenomena and not organisms). I would speculate that viruses were originally designed to allow the designed cells to cross-talk extensively. More specifically, I envision cells designed with the program to disperse part of their genetic constitution laterally through a life-cycle-like stage that involved replicating and packaging genetic material for dispersal. In short, I speculate that what we now know as ‘viruses’ were originally a designed sex-like mechanism for unicellular organisms, important for establishing a foothold on a sterile planet (I call them viretes). Possible expressions of this mechanism might include:
a. A cell suicide program coupled to the packaging of genetic material for dispersal.
b. An endospore-like program, where instead of forming a spore around the replicated DNA, the DNA is packaged in virus heads which in turn are packaged into a “release” cell.
c. Controlled exocytotic release.
I would further speculate that such sex-like mechanisms may have been important in the early stages of the designed founder effect allowing the heterogeneous cells to adjust, as a consortium, to an unfriendly environment. During this adjustment phase (analogous to the latent phase in a bacteria growth curve), the cells shuffled their material and hit upon global-adaptive state whereby the importance of such transfer was decreased. We still see “rusty remnants” of this state carried on by the vestiges of transposons, natural transformation, and yes, viruses.
Well, almost 10 years later, it’s looking like I was on to something:
In the ocean, genes can hop between bacteria with unexpected ease, thanks to strange virus-like particles that shuttle genes from one species to another1. These particles, called gene-transfer agents (GTAs), insert DNA into bacterial genomes so frequently that gene transfer in the ocean may occur 1,000 to 100 million times more often than previously thought. This suggests that GTAs have had a powerful role in evolution.
GTAs, which harbour bits of their host’s genome inside a protein coat, reside in bacterial genomes. When they exit, they take some of their host’s genes with them.
“GTAs are very peculiar,” says Eugene Koonin, an evolutionary biologist at the National Institutes of Health in Bethesda, Maryland. “Their only function seems to be transferring genes.”
Horizontal gene transfer can also occur through direct cell–cell contact or by means of mobile genetic elements called plasmids, or by bacterial viruses — which often destroy the host upon departure. GTAs are virus-like, but they don’t seem to take a toll on their host and, what’s more, seem to efficiently shuttle genes between unrelated bacteria.
It’s worth emphasizing that these GTAs do not apparently harm the host and do spread information between species. This is the logic of the ‘virete’ that I had in mind as it indicates bacteria are all connected into some type of super-organism. And not only do different species communicate genetic information back-n-forth, but don’t forget that different species can communicate more directing through quorum sensing.
And all of this ties into four related major themes I have been outlining over the years:
- Bacteria as terraforming agents.
- There may be no such thing as a “unicellular life form.”
- The “environment” as living (adding a deeper intrinsic nature to evolution).
- Homeostasis – we can begin to think of this bacterial super-organism as building a global biosphere much as a colony of termites build a termite mound.