Technically Speaking: Alpha-Proteobacteria

The evolution of Eukaryotes is thought to have resulted from several major symbiotic events. This technical document describes the alpha-proteobacteria as an important initial source of genetic diversity among eukarya, as described in the background of this article. Ancestral relatives of these germs are thought to have provided the original mitochondrion.

The alpha-proteobacteria are a highly intriguing group, being identified in Rickettsia and subcuticular bacteria, a poorly understood endosymbiont in marine invertebrates. Furthermore, alpha-proteobacteria are thought to be the cause of juvenile oyster disease (JOD).

So, the alpha-proteobacteria are thought to 1) have been the precursor to eukaryotic mitochondria, 2) are curious, poorly understood endosymbionts of at least one highly successful phylum of marine invertebrates, and 3) are causative agents of disease in both marine organisms and man. But, there's more. One diverse group of alpha-Proteobacteria are those belonging to the genus Wolbachia. This intracellular symbiont is known to occur among a wide array of arthropods, often affecting the reproductive fitness of their hosts. More on Wolbachia can be found here. There is much current research involving genome mapping of Wolbachia from a variety of hosts archived in massive databases.

Are these microbes providing us a modern picture of earliest evolutionary events from which life diversified? Are there any examples of alpha-proteobacteria that are not pathogenic/parasitic, but rather represent a symbiont in a commensal or mutually beneficial arrangement?

What Is Phoresy?

Phoresy is a type of symbiosis in which one organism "uses" another for transportation. This example, is a rather disgusting one, in which a parasitic fly (the Torsalo Fly) utilizes other parasites (in this case a mosquito) to adhere its eggs to. Upon contacting its warm blooded meal, the mosquito, concerned only about its own well being, provides the attached parasites eggs to begin development.

This would appear as a highly co-evolved parasitism in that the vector is actually another parasite. The bot fly itself is a parasite during the larval stage of its life cycle. During the adult stage, however, it relies on another organism to fulfill its work in distributing its offspring.

More detail on this rather ugly human parasite is here, to which we credit the image above.

Google:Symbiosis

On occasion, I run a Google search for "symbiosis" just to see what the latest biology on the web describes for the term. At the number one spot today came The Symbiosis Institute of Business Management, the link to which is not currently working. I just find it noteworthy that a Business Management school (its a .edu extension) would find the top slot for symbiosis! Can biology catch a break?

The apparent importance of symbiosis in business decisions notwithstanding, the #2 search return came back with this, an informative, if not very sexy, website for a biology curriculum: Kimball's Biology Pages. A brief perusal of the page shows Dr. Kimball's thorough understanding of symbiosis and its importance in modern applied science. He describes the three major types of symbiosis starting with mutualism and ending with parasitism. The page concludes with a brief speculation on how symbioses evolve. "It seems plausible that what begins as a parasitic relationship might over the course of time evolve into a mutualistic one as the two organisms evolve to minimize the damage to the host."

This process, he indicates, is supported by Kwang Jeons work with amoebae. This appears to be the current working model of the evolution of symbiosis and deserves much future discussion on this blog. The other important take away from this position is that it implies a "complex homeostasis" in symbioses, an area I devote a bit of attention to below.

The Jeon ameoba example suggests an energetic imbalance that is corrected by co-evolution. As a parasitic relationship, is the driving force, as Dr. Kimball asserts "the two organisms evolve to minimize the damage to the host"? This area is worth a closer look.

Image courtesy of the Center for Biological Sequence Analysis. No copyrights are known.

The Applied Science of Symbiosis

Happy Day After Darwin Day!

An interesting article from MSNBC published today regarding the conversion of biomass to fuel using gut bacteria from insects and cellulolytic fungi. This area holds alot of promise in reducing the costs of synthetic fermentation in my opinion.

Check it out.

The significant phrase "directed evolution" caught my attention....

Through a genetic modification known as directed evolution, Iogen has souped up fungus microbes so they spew copious amounts of digestive enzymes to break down straw into sugars. From there, a simple fermentation — which brewers have been doing for centuries — turns sugar into alcohol.

...as did the closing paragraphs.

At the California Institute of Technology, Jared Leadbetter is mining the guts of termites for possible tools to turn wood chips into ethanol. Leadbetter said there are some 200 microbes that live in termite bellies that help the household pest convert wood to energy.

Those microbes or their genetic material can be used to produce ethanol-making enzymes. So scientists at the Energy Department’s Joint Genome Institute in Walnut Creek, Calif., are now sequencing the microbe genes in hopes of finding a key to ethanol production.

“We have this idea that microbes are pests,” said Leadbetter, who has been studying termite guts for 15 years. “But most microbes are beneficial.”


Photo of worker termites courtesy of M. Potter, Univ. of Kentucky.

The Role of Symbiosis in Physiology and Evolution

This link provides an overview of the types of symbioses and some of the players involved in their research. From the conference abstract...

A variety of new and exciting models of symbiotic associations have been developed to investigate symbiotic relationships among organisms, their role in physiology, and especially the evolution of the organisms involved. The association host/symbiotes creates a new biological unit, the symbiocosm, itself subject to natural selection.

Different types of association exist as demonstrated by six different models. The symbiotes can be outside (ectosymbiosis) or inside the host, in the intestine or in some invaginations of the integument (endosymbioses), or inside the cells (endocytobioses). In integrated symbioses the symbiote (a bacterium) is perfectly controlled by the host (location and number), and looklikes a new cell organelle, only transmitted to the progeny by the mother. In other cases the symbiote is not perfectly controlled and invades most cells (Wolbachia), but not the entire the host population.

In the Squid-Vibrio model (extracellular symbiosis), the bacterium is transmitted horizontally, or cyclically, and can be grown in vitro. The colonization of the luminous organ modifies processes of recognition and specificity. Another endosymbiosis is that seen among termites. The gut lumen harbours protozoa and/or bacteria. They help the digestion. Transmission is horizontal. A coevolution host/symbiotes is highly probable.

Among endocytobioses another model is a protozoan, the amoeba, living symbiotically with a bacterium. The formation of the symbiosis has been observed in the laboratory. The bacterium, which was originally a parasite, has coevolved with the host cell thereby becoming obligate and thus integrated. The role of symbiote in co-evolution is also spectacular with the Wolbachia model, a bacterium associated with many insects and other invertebrates.

The aphid model presents an integrated and obligate symbiosis. The changes of the symbiotic bacterium during symbiosis are spectacular, most notably the reduction of the genome, which has been recently sequenced.

A last model is a weevil (Coleoptera), where symbiosis is perfectly integrated, but surprinsingly not always obligate. Comparison of symbiotic and aposymbiotic strains that lack symbiotes allows an understanding of the exact role of symbiosis. The symbiocosm is there controlled by interactions of four different genomes: nuclear, mitochondrial and symbiotic (principal endocytobiotes and Wolbachia).

Symbioses appear as important factors in evolution. Consequently, symbiology must be recognized as an important field of Zoology, Botany and Genetics.