GREEN JELLY BALLS OF OPHRYDIUM VERSATILE: HIDDEN RELATIONSHIPS IN POND SLIME

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GREEN JELLY BALL, MID MAY

Drifting along the bottom of Laurel Lake in western Massachusetts' Erving State Forest are balls of green pond slime. At first glance, a diver or snorkeler who is not familiar with these green jelly blobs may think, "Wow, look at all this pollution!" But it is not pollution that has invaded this pristine lake known for its springtime showing of copulating newts.

NEWT SEXUAL REPRODUCTION IN MAY

Fortunately for the newts and other beings that live in and use the lake, these green jelly balls are living colonies of a variety of microorganisms that have formed symbiotic relationships with a host organism known as Ophrydium versatile. Only with the aid of a microscope can the fascinating world inside the Ophrydium jelly balls be seen.

Ophyrdium versatile is a eukaryotic single-celled ciliate from the kingdom Protoctista that forms gelatinous colonies. Colonies of Ophyrdium are found 3-10 feet deep in the photic zone of slightly acidic bogs and ponds. The photic zone is the portion of water where sunlight is able to penetrate. Colonies may be lying on top of the sediment in shallow waters, drifting in the water column or attached to aquatic plants such as milfoil (Myriophyllum) of pondweed (Potamogeton).

OPHRYDIUM ATTACHED TO AQUATIC VEGETATION

You even may have seen Ophyridium colonies and misidentified them as spotted salamander eggs or mats of cyanobacteria.

MASS OF SPOTTED SALAMANDER EGGS WITH EMBRYOS

These green jelly balls range in size from under 2 cm to over 30 cm. The smaller balls are flat and kidney shaped and the larger ones are an irregular doughnut shape which may contain a "hollow" region of gas and water in the center. Most gelatin matrices are formed by mid-spring and grow until mid-fall, with an explosive growth period in July and August that sometimes doubles the size of the colonies. Some very small colonies have been found in the water of warm bogs during the winter. It is still a mystery to scientists why the gel matrix forms or why it disappears, but some scientists believe the day length, the amount of sunshine and/or the temperature of the water play as much a crucial role as individual microorganisms in the life span of the green jelly balls. The only thing known about the formation of the colonies is that Ophrydium individuals or zooids are capable of separating from their holdfast roots in the gel and swimming freely to populate other areas. These free swimmers are called telotrochs. They usually attach themselves to suitable substrates such as aquatic plants and then return to the immobile zooid form.

OPHRYDIUM ZOOID IN THE MOBILE TELOTROCH STAGE

Ophrydium versatile individuals are shaped like little eyebrows from which they are named (ophrys=eyebrow, Greek). These cells are 300 um -400 um long when extended and 100 um-200 um when contracted. Environmental stimuli such as changes in light or temperature may cause all the zooids in the gel to contract sporadically and to expand in unison. They are held in place in the two or three most peripheral layers of the gel in evenly spaced alternate patterns by their flagellum-like holdfasts. These holdfasts may be two or three times as long as the cell itself.

OPHRYDIUM CILIATE ARRANGEMENT IN A JELLY MASS

In these outer layers the predaceous zooids are able to feed upon bacteria, fungi, protozoa, algae or almost any microscopic entity in the water. Two spirally-shaped rows of cilia, located around each zooid's oral pore or mouth, create a current of water that "sweeps" in unsuspecting prey from the surface of the gel and outer lying gel layers into its body cavity for digestion.

ZOOID FULLY EXTENDED. NOTICE THE SPIRALED ROWS OF CILIA AROUND THE ORAL PORE (ARROW)

Common to most of the 8,000 known freshwater and marine ciliates and unique to all protozoa, each Ophrydium zooid has two types of nuclei: macronuclei and micronuclei. Some ciliates may have one or more of either kind. The macronucleus, developed from micronuclei precursors, is polyploid, that is it contains from 40 to 500 copies of DNA. Shaped like a ribbon throughout the cell, the macronucleus is made of pieces of DNA called chromatin which contain hundreds of copies of only a couple of genes. The sole purpose of the macronucleus is the production of messenger RNA for cell growth and functions. Without it the cell will not live. Micronuclei, however, are not necessary for sustaining the life of the cell because they play no role in growth or cell division. Micronuclei are diploid (two copies of DNA) and are used only for sexual reproduction and inheritance. While ciliates reproduce in many ways, O. versatile reproduce like all peritrichs, by transverse binary fission. Little is known about the sexual stage of peritrichs, the order of ciliates to which O. versatile belong.

One of the most interesting facts about Ophrydium jelly balls is where they get their greenish color. The color is partly due to an endosymbiotic relationship each zooid has with green algae. Many green algae actually live inside Ophrydium versatile cells! Between 400-500 Grasiella coccoids, only 3 um-5 um long, call each zooid their home. These Grasiella coccoids contain chlorophyll a and b and are photosynthetic. It is thought that the green algae live in the Ophrydium because the algae need carbon dioxide and large amounts of sunlight to survive. They are autotrophic and, similar to plants, they make their own food. Since Ophrydium zooids live in the outer layers of the gel, the endosymbiotic green algae receive light which they need for photosynthesis while, at the same time, obtain carbon dioxide from zooid respiration.

ENDOSYMBIOTIC GREEN ALGAE LIVE INSIDE EACH ZOOID WHILE ZOOIDS AND SYMBIOTIC DIATOMS (AND OTHERS) LIVE TOGETHER IN THE JELLY BALLS. ARROWS POINT TO HOLDFASTS ANCHORING THE CILIATES IN THE GEL.

Symbiotic relationships between individuals imply that all organisms benefit from the relationship. If so, what is it that the zooids receive in return? Researchers have speculated upon many possible benefits obtained by the ciliate cells from the algae including: protection from harmful ultraviolet light by the filtering characteristics of the photosynthate pigments of chlorophyll, oxygen produced by the algae may be used in zooid respiration and perhaps the use of other metabolites produced by the algae that the zooids require to survive. One metabolite being investigated is the sugar, maltose, which the algae excrete in low pH environments like the bogs and ponds where Ophrydium jelly balls live.

Another symbiotic relationship that may be even more important to the jelly balls is the one that exists between O. versatile and protoctist diatoms.

DIATOM; AN ALGAL GROUP WITH CELL WALLS OF SILICA (GLASS). FOSSIL DEPOSITS OF DEAD DIATOMS ARE MINED FOR DIATOMITE, AN ABRASIVE IN TOOTHPASTE.

Diatoms are found in all aquatic habitats including snow and rain, but their association with the complex Ophrydium jelly balls is a novel habitat for them. Although diatoms only constitute about 12% of individuals in the waters where Ophrydium are found, they are 90% of all the other life forms inside these gel masses. It is possible that two species of diatoms, Cymbella and especially Nitzchia, hold the secret to the production of the Ophrydium gel. One reason is the great number of diatoms in the gel and their proportionality to Ophrydium versatile ciliates. The other is that Nitzchia produce gelatinous tube-like strands themselves. Somewhere between the two, ciliates and diatoms,

MORE DIATOMS

could be the answer to the production of Ophrydium jelly balls.

A number of other occupants and unknown relationships exist in the jelly, including: protists such as other ciliates, mastigotes, euglenids, chlorophytes, heliozoa, desmids

DESMID, A MEMBER OF THE CHLOROPHYTA (GREEN ALGAE). EACH CELL HAS A CONSTRICTION RESULTING IN TWO (2) SYMMETRICAL HALVES.

and six species of diatoms.

CHAIN OF DIATOM CELLS

Representative of the prokaryotic jelly ball symbionts are filamentous and coccoid cyanobacteria, large rod shaped bacteria and at least three types of spirochetes. Very few fungi have been found. In the water reservoirs of the larger Ophrydium masses, the Animalia kingdom is represented by rotifers, sponge spicules, nematodes, platyhelminths, cladocerans, harpacticoids and copepods. Many species that live in these gel masses or travel through them have not been identified. The relationship between most of these gel inhabitants is not fully understood; together they make a virtual zoo of microscopic life found in the shallows of freshwater ponds and bogs.

Like a living analog of the Proterozoic era some 700 million years ago, these bog and pond jellies represent protist colonies from the "garden of Ediacara" where differing soft-bodied individuals banded together to form one functional being for the purposes of protection from predation, desiccation and ultraviolet radiation. Next time you see some pond slime or green jelly balls in the water, think about the mosaic ecosystem they represent. These symbiotic relationships between the different forms of life in the gel masses could possibly explain the cosmic processes that started life on Earth, how it has changed since, and what it might be like millions of years in the future!

References:

Brock, T.D. et al. (1994) Biology of Microorganisms. Prentice-Hall, Inc.

Englewood Cliffs, NJ, pp 854-856.

Duval, B. and L. Margulis. (1995) The Microbial Community of Ophrydium versatile

Colonies: Endosymbionts, Residents, and Tenants. Symbiosis 18:181-202.

Goff, L.J. and J. Stein (1981) Digestion in the Peritrich Ciliate

Ophrydium versatile. Protoplasm 107:240.

Margulis, L (1988) Five Kingdoms. W.H. Freeman and Company, NY, pp 120-121.

Margulis, L and D. Sagan (1996) Gaia to Microcosm. Kendall/Hall Publishing Co.,

Dubuque, Iowa, pp 73-97 (With accompanying video at the New England Science Center, Worcester, MA).

Strickberger, M. (1990) Evolution. Jones and Bartlett, Boston, pp. 272-273.