~~~ Bacteria Have Babies! No Kidding! ~~~

If you read The Big One! in this series of articles, you will remember, "A single-cell organism has been found that is large enough to trip over!" Discovered by Dr. Fishelson, the bacterium, Epulopiscium fishelsoni, is one member of Epulopiscium spp. which, in a symbiotic relationship, lives in the gut of a Red Sea surgeonfish - to wit:


Ha! You had to look at my surgeonfish drawing again.... now, quit groaning.... I can hear you.... <grin>.

"Normal-sized" bacteria range in size from about 0.2 µ-meters (micrometers) to about 1.5 µ-meters. Since the lower-limit of the human eye to discern an object is approximately 200 µ-meters (200 µ-meters means 200 millionths of a meter), we can't see most bacteria without the aid of a microscope (If you wish, take a look at How to Measure Cells to find a little bit of information on how microscopes work, and how we can see tiny things). Members of Epulopiscium bacterial species are approximately 250 µ-meters long! And, believe it or not, the bacteria within this genus actually have babies - live babies!

There have been several publications which refer to these observations, but, I will talk mostly about one summary article which you may find easier to locate in your local library. This well-written article, recently published in the May, 1996 issue of the American Society for Microbiology News, or as us folks call this publication, ASM News - Volume 62, Number 5, pages 243-244. describes the following findings:

Publications by (1) Clements, et. al., (2) Fishelson, et. al., and (3) Montgomery and Pollak, established that this organism generates living cells inside it - and therefore produces, like mammals, vivaparous offspring! The term, "vivaparous", is used to describe the production of live young from within an organism, as opposed to eggs. For Epulopiscium spp., there are usually two (some Epulopiscium species apparently produce more than two) little living bacteria produced within the mother cell, and these "babies" are released through a little slit that opens at the end of the mother cell (due to a type of programmed lysis - cell dissolution). The little bacteria begin to form at one of the ends of the long mother cell, and after cell wall synthesis is complete for each cell, the little bacteria are released - to grow into the large-sized, normal "adult". Eventually, these cells will themselves bear offspring!

One of the things I'm very curious about, but can't yet find any information to answer my question, is, how do all of the chromosomes get made? In order for these little cells to be alive and viable, each must have a complete chromosome - a double-stranded, helical, super-coiled, closed-circular chromosome made of DNA. And, I assume the mother cell retains its chromosome as well, for awhile at least - I'm not sure. Maybe there is condensation of the mother cell's chromosome and one baby cell is made around the chromosome inside the mother cell. Then, possibly this new cell divides at least once in the normal way for bacteria, e.g., by a process called binary fission, which produces two little cells inside the mother cell. The completion of this process within the mother cell could possibly trigger gene activation which begins the programmed lysis sequence, which would eventually result in the release of the "children." I have no idea how this bacterium accomplishes such a feat.

Further, each of these little cells, along with the mother cell, must have ribosomes (protein-synthesis machinery) and cytoplasm containing all of the necessary enzymes, etc., which must be distributed to these little cells. Additionally, each of these little cells must have a complete cytoplasmic membrane and a complete cell wall structure surrounding them or else these cells would not be able to survive (for some info on the cell wall of bacteria, please see What the Heck is Penicillin?).

In reading the ASM News article, I located one of the referenced publications by Norman Pace and colleagues (Angert, Brooks, and Pace, "Phylogenetic Analysis of Metabacterium polyspora: Clues to the Evolutionary Origin of Daughter Cell Production in Epulopiscium Species, the Largest Bacteria."; Journal of Bacteriology, 178: 1451-1456, 1996). This article examines the genetic relationship between members of Epulopiscium and the bacterium Metabacterium polyspora. The bacterium M. polyspora is one member of many different bacterial species which reside symbiotically in the cecum (a part of the digestive system) of the guinea pig. I know - who in the heck would look in there? <grin>.... Anyway, this organism makes babies, too! But, these babies are endospores - meaning - a very specialized form of a bacterium is generated which is in a state of "suspended animation." (a quiescent form of the organism). An endospore is essentially devoid of metabolic activity until when environmental conditions become favorable, the endospore can convert and become what is know as a vegetative cell - one which divides normally, and is metabolically active, i.e., "alive" again, and no longer quiescent. For example, endospores more than 3,000 years old can be found associated with Egyptian mummies. In the case of M. polyspora, several of these endospores form inside the mother cell, and, these endospores are released when the mother cell lyses (falls apart).

The formation of multiple endospores is an unusual event; however, endospore formation per se is not all that unusual among bacteria: the soil-living genus Clostridium does this routinely. This bacterial genus is the one responsible for the production of the deadly tetanus and botulism toxins (botulism toxin is the most potent - the amount required to be lethal - of all of the natural toxins ever identified). Therefore, this genus in particular is one of the main reasons that pressure cookers are necessary (please see: Hey! Better Use a Pressure Cooker!) - this treatment kills the spores - and at the same time destroys the activity of the toxin - therefore, we protect ourselves from vegetative cell formation and the resultant toxin production by Clostridium botulinum in our canned food.. Yaaayyy!. Endospores are really tough - to kill them requires at least 121 degrees Celsius for about 20 minutes. As for tetanus toxin, the toxin made by Clostridium tetanii, we of course routinely (you'd better!) receive tetanus vaccinations. These vaccinations stimulate each time, about a 10 year-long protective response by our immune system.

The reason that Pace and his colleagues have been examining Metabacterium polyspora and Epulopiscium, is because these investigators are in the business of determining the genetic connections among different bacterial species. The process used is to examine the sequence of what is known as ribosomal RNA (16S r-RNA, in particular). This type of RNA is an integral part of the structure of ribosomes, and the 16S rRNA sequence is unique to a given species of bacteria, and can therefore be used to identify a bacterial species and closely related species (the "S" stands for "Svedberg" co-efficient - one measurement of the size of something - 19S is about one million molecular weight, and 7S is about 150,000 molecular weight). As it turns out, when these scientists compared the sequences of the 16S rRNA's isolated from each of these bacterial organisms, the sequences were similar enough to show these two bacteria are pretty closely related to one another. Pace and his colleagues state in the abstract of the J. Bact. article: "On the basis of this result and other correlations, we propose that the process of sporulation was modified in a predecessor of Epulopiscium spp. to produce live offspring instead of quiescent endospores."

Therefore, it looks like way back in evolution, bacteria came up with a way to make offspring in a quiescent form (endospores), and then later evolved to produce live offspring. Because of the recent discoveries that bacteria have proteins that were only a few years ago thought to be only in higher organisms like us (eucaryotes - cells with chromosomes enclosed within a defined organelle called a nucleus), and now the fact that bacteria actually produce live offspring, maybe we had better re-think how we perceive these simple organisms! These little critters don't appear to be simple by a long shot! I think that all of this newly-discovered information is absolutely wonderful... In fact, one thing I found out the other day.. hmmm, can't remember where I heard this information... anyway, what I found out is that it is estimated that 99 percent of the bacterial species on our planet remain unidentified!. I cannot imagine what we will understand about all living things 50 years from now - but - I would really like to be around to find out.... Wow!

Unfortunately, the chances of my being around - well, alive and kicking that is - 50 years from now don't look too promising... I'd be over 100 years old.... but then, I had a couple of great-great aunts, a grandmom and a granddad make it past that age.. so - Who knows? Maybe my genes haven't been too damaged by all of my leaping around <grin>.

1. Clements, K.D., D.C. Sutton, and J.H. Choat. 1989. Occurrence and characteristics of unusual protistan symbionts from surgeonfishes (Acanthuridae) of the Great Barrier Reef. Australia. Mar. Biol. 102:812-826

2. Fishelson, L., W.L. Montgomery, and J.A.A. Myrberg. 1985. A unique symmbiosis in the gut of tropical herbivorous surgeonfish (Acanthurdiae: Teleostei) from the Red Sea. Science 229:49-51

3. Montgomery, W.L., and P.E. Pollak. 1988. Epulopiscium fishelsoni, n. g., n., s., a protist of uncertain taxonomic affinities from the gut of an herbivorous reef fish. J. Protozool. 35:565-569.

Copyright John C. Brown, May, 1996

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