Expert: John Locke - 8/27/2007

Question
Hello! I have a question that I have tried to find the answers to myself for quite a while now, but I have failed. I would like to know if it is possible for a prokaryote to have a multicellular form. I know that they can be colonial and undifferentiated or colonial and partially differentiated (such as cyanobacteria), but can they ever be truly multicellular? If so, have we ever found any such organism living or dead? (Or posssibly fossilized?) Or could it even exist, if only in theory? Thanks so much and no rushon the answer- I am sure you have more important questions waiting to be answered. Mine is just curiosity. Thanks again!

Answer
Thanks for using AllExperts, Stan.

You've preempted the standard response to this question by mentioning the colonial forms of prokaryotes; these are the one of the most familiar multicellular-like prokaryotic organisms. As you probably already know, some of the colonial forms have cells with distinct, though partial, differentiation; that is not the only multicellular form of prokaryotic life, however--enter the multi-celled magnetotactic prokaryote (MMP). This is a multi-celled prokaryote with a somewhat higher level of organization than simple colonial behavior.

Magnetotactic prokaryotes were discovered in the 1970's; they're bacteria capable of orienting themselves according to the earth's magnetic field via the manipulation of ferrous molecules (iron-containing compounds, of course, are affected by the earth's magnetic field). More recently, a unique multi-cellular form of these bacteria has been discovered, the MMP. An MMP exists throughout its lifespan as a motile, hollow ball of cells that is capable of reproducing as a whole--the individual prokaryotes all divide simultaneously, and then two groups of cells separate to form two new MMPs. This necessarily means that all the bacteria within an MMP are genetically identical, and MMP's as a whole appear to be descended from the proteobacteria (the group, incidentally, that contains pathogenic bacteria like Salmonella and the cholera organism). Prokaryotes that make up the MMP appear to exist only as part of the whole structure and have never been found free-living; indeed, the individual prokaryotes die when removed from the MMP. Like their unicellular magnetotactic counterparts, MMPs are capable of orienting themselves to the earth's magnetic field.

The MMP was only discovered relatively recently, so the references that I give below are necessarily from the scientific literature. It may be difficult to access these from anywhere other than a university that has access to the relevant journals online, so please be aware of that. There are few resources now available on MMPs for the general public, unfortunately.

http://www.biophysj.org/cgi/content/abstract/88/2/1496

Unexpected diversity in populations of the many-celled magnetotactic prokaryote. Simmons SL, Edwards KJ. Environmental Microbiology 9(1):206-15. January 2007.

Multicellular life cycle of magnetotactic prokaryotes. Keim CN, Martins JL, Abreu F, Rosado AS, de Barros HL, Borojevic R, Lins U, Farina M. FEMS Microbiology Letters 15(2):203-8. January 2004.

The MMP continues to be an active area of research, both for its own sake and for its potential applications in electronics and chemical manufacture. While more multicellular prokaryotes may be discovered in the future, the MMP now the only known example of a highly-organized multicellular prokaryote.