2004 年 32 巻 2 号 p. 96-108
During a period of not so far after the origins of life on earth, symbiotic microbial cooperation in some way must has started. Kato and Shimizu proposed a name of “pristine ecosystem” to such the symbiotic cooperation (microbial interaction), because it could be positioned at origins of ecosystem. However, the scene of structure and function of the cooperation has not become evident. Sulfur-turf is filamentous microbial mat growing in hot spring effluents, and the filament of the mat consists of a few sulfur-oxidizing bacteria (large sausage-shaped and small curved), sulfur particles, and cellulose as a matrix substance. Here, we took up sulfur-turf as a model of pristine symbiotic cooperation, and discussed a possibility of the correlation of filament structure, specially emphasized the roll of cellulose-core, with three steps of a series of sulfur-oxidizing reaction; hydrogen sulfide to sulfate via elemental sulfur and thiosulfate. Sulfide oxidation probably proceeds at the outside of the filament or of the mat by sausage-shaped bacteria and resulting elemental sulfur. As both of elemental sulfur and cellulose are hydrophobic, sulfur particles may be concentrated around cellulose-core of the filament where microaerophilic conditions are prevailed, and is oxidized to thiosulfate by sausage-shaped bacteria or by curved bacteria. Thiosulfate decreases pH value around the cellulose-core and is oxidized to sulfate. The significance of cellulose as matrix substance in the steps of sulfur-oxidation should be emphasized. Pristine symbiotic cooperation may have started in microbial mats as syntrophic, namely as a style of substrate chain and in a manner of exosymbiotic relation.
