Zoothamnium niveum
| Zoothamnium niveum | ||||||||||||
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| Scientific name | ||||||||||||
| Zoothamnium niveum | ||||||||||||
| Ehrenberg , 1838 |
Zoothamnium niveum is a type of unicellular eyelash animal . The species forms feather-shaped colonies in shallow sea regions. It lives in symbiosis with sulfur-oxidizing bacteria of the species Candidatus Thiobios zoothamnicoli, which cover the entire surface of the colony and give it a strikingly white color.
features
The dazzling white plumage-shaped colonies consist of individual, bell-shaped cells (zooids). The stems of the individual individuals branch out alternately from a central stem. This creates a colony of up to 15 mm in height from hundreds of individual zooids with a length of only 120 micrometers. With the help of a central muoneme that runs through the stems of the entire colony, the colony can contract into a spherical tuft like lightning.
Their white color comes from chemoautolithotrophic sulfur bacteria that cover the entire Zoothamnium colony as a coating . In other Zoothamnium species, only the stalks are known to be covered with bacteria. The bacteria contain elemental sulfur, which gives them their white color. Without the bacterial population, Zoothamnium niveum is colorless.
As with other ciliate animals, the contractile vacuole ensures the exchange of salt and thus survival within the salt concentrations of sea and brackish water. In Zoothamnium niveum it is just below the lip formation of the peristome .
Polymorphism
Typical ciliates are normally organisms that live as single cells in water and manage all vital functions such as nutrition, metabolism and reproduction. However, colonies of Zoothamnium niveum consist of many hundreds to thousands of individual cells, which together form a complex organism. This is referred to in its entirety as the "giant ziliate".
A zooid polymorphism can be seen under the microscope on older branches of the colonies . Three different forms of the individual cells differ in construction and function. There are larger macrozooids that can transform into swarms and detach from the colony. They settle in suitable locations and form new colonies. The microzooids are smaller phagocytes that nourish the colonies by ingesting the symbiotic bacteria and other swirling particles. At the terminal end of the colony, there are special zooids which, by dividing the cell lengthways, ensure that the colony reproduces asexually.
There is also a dimorphism in bacteria. On the stems they are rod-shaped, and near the ciliate mouth disc of the microzooids they have a spherical (coccoidale) shape. In between there are transitional forms.
distribution and habitat
The sessile colonies of Zoothamnium niveum were first described from shallow water areas of the Red Sea . They were later found off the Florida Keys in the Gulf of Mexico and on the Barrier Reef off Belize in the Caribbean .
Zoothamnium niveum colonies settle in groups in a sulphide-containing environment. Hydrogen sulphide , sulphides and related sulfur-containing intermediates such as thiosulphate are formed as decomposition products of organic material. Parts of plants such as the torn off leaves of Poseidonia oceanica in seagrass meadows in the Mediterranean collect in hollows or under rocky outcrops and rot. In the mangrove swamps in the Caribbean, organic material can be processed into peat by releasing hydrogen sulfide. There are also natural escape points of hydrogen sulfide under certain geological conditions such as at the submarine hydrothermal vents z. B. off the Canary Islands .
Ecological conditions
Extreme ecological conditions prevail at the points where hydrogen sulphide is released and where colonies of Zoothamnium niveum settle. Since there is little current under the mangrove roots and seagrass depots under rocks, the area surrounding these decomposition depots is very low in oxygen and rich in sulfide. In this respect they are similar to the conditions at hydrothermal springs in the deep sea, the black smokers . However, in the shallow water there are even temperatures of 28 ° C in the Caribbean and 21 ° C to 25 ° C in summer in the Mediterranean, while temperature differences between over 300 ° C and 2 ° C occur at the volcanic vents of the deep sea. The Zoothamnium colonies do not settle directly on the surface of the decaying matter, but rather sit nearby on overhanging rocks or floating seagrass leaves and perch, as well as on mangrove roots.
symbiosis
The symbiotic performance of the colonies of Zoothamnium niveum for the bacteria that cover them, Candidatus Thiobios zoothamnicoli from the group of Gammaproteobacteria, consists in actively promoting the change between the oxygen-rich and sulphide-rich environment. This change can be ensured by the regular contraction and extension of the colonies and the swirling activity of the eyelashes in the area of the ciliate's mouth.
The rapid contraction and the slow expansion of the colonies creates a flow around which, on the one hand, sulphide-rich water is available for the nutrition of the bacteria and, on the other hand, normally oxygen-rich seawater is available for the respiratory processes of Zoothamnium niveum . This mixture can also be regulated by the eyelashes around the mouth disc of Zoothamnium . If the supply of sulfur compounds is too low, the bacteria first use the sulfur stored in their cells. However, they become pale and translucent after just four hours because the sulfur supply has been used up. Conversely, too high a sulfide content can damage both the bacteria and the Zoothamnium niveum colony due to its poisonous effect .
By optimizing the content of oxygen and sulfur in the water with the help of the ciliate, the bacteria at the oral end of the microzooids have a spherical shape and thus a larger volume and a higher rate of division than the rod-shaped bacteria of the same species Candidatus Thiobios zoothamnicoli on the stems. The bacteria in the area of the mouth can serve as a source of food and are tumbled into the cytostome and digested.
Individual evidence
- ^ Christian Rinke, Raymond Lee, Sigrid Katz and Monika Bright: The effects of sulphide on growth and behavior of the thiotrophic Zoothamnium niveum symbiosis. Proceedings of the Royal Society, Biological Sciences, 274 (1623), pp. 2259-2269, September 2007, PMC 1950315 (free full text) (Eng.)
literature
- Christian Rinke, Jörg A. Ott and Monika Bright: "Nutritional processes in the chemoautotrophic Zoothamnium niveum symbioses", Symposium of the Biology of Tropical Shallow Water Habitats, Lunz, Austria, October 2001, pp. 19-21
- Christian Rinke, Stephan Schmitz-Esser, Kilian Stoecker, Andrea D. Nussbaumer, David A. Molnar, Katrina Vanura, Michael Wagner , Matthias Horn, Jörg A. Ott and Monika Bright: “Candidatus Thiobios zoothamnicoli,” to Ectosymbiotic Bacterium Covering the Giant Marine Ciliate Zoothamnium niveum. Applied and Environmental Microbiology, 27 (3), March 2006, pp. 2014-2021 abstract