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BIOTIC RELATIONSHIPS BETWEEN SOIL ALGAE AND OTHER MICROORGANISMS

1961; Wiley; Volume: 48; Issue: 2 Linguagem: Inglês

10.1002/j.1537-2197.1961.tb11624.x

1537-2197

Bruce C. Parker, Harold C. Bold,

Diatoms and Algae Research

P arker , B ruce C., and H arold C. B old . (U. Texas, Austin.) Biotic relationships between soil algae and other microorganisms. Amer. Jour. Bot. 48(2): 185–197. Illus. 1961.—A study was conducted of biotic relationships between various algae and other microorganisms isolated from a sample of Texas soil. From 143 two‐membered combinations of organisms tested in soil‐water cultures, 3 were selected for detailed studies of the nature of the causal mechanisms of the associative effects. These were: (1) an association between a species of Bracteacoccus (Br. A‐20) and a heterotrophic bacterium (B‐6); (2) an association between a species of Chlamydomonas (Ch. 10) and a species of Streptomyces (Act‐1); and (3) an association between a blue‐green alga, Phormidium sp. (Ph. 14), and an as‐yet‐unidentified fungus (F‐2). In the first association, the heterotrophic bacterium increased growth of Bracteacoccus up to 20 times in soil‐water culture; the chief cause of stimulation was shown by a series of experiments to be the decomposition by the bacterium of complex nitrogenous substrates in the soil resulting in the release of simplified products which were available to the alga as a nitrogen source. In soil‐water culture, Streptomyces (Act‐1) enhanced the growth and motility of Chlamydomonas (Ch. 10) and induced akinetogenesis in the alga, while the actinomycete itself was stimulated in growth and production of conidia. The mutual stimulation was shown to be caused, in part, by carbon dioxide‐oxygen interchange between the organisms. Motility of Ch. 10 was enhanced by a decrease in nitrogen as a result of the growth of Act‐1 and by the ability of Act‐1 to decompose and assimilate the extracellular polysaccharide of the alga. The assimilation of the extracellular polysaccharide by the actinomycete promoted its growth and conidia production. Initiation of akinetogenesis in Chlamydomonas occurred exclusively in close association with the filaments of Streptomyces in soil‐water cultures, and only when the concentration of available nitrogen dropped below a critical level. The akinetogenic factor has not yielded to isolation and identification, but there is some suggestion that it may be an antibiotic substance. Phormidium (Ph. 14) was frequently antagonized and annihilated by fungus 2 in the soil‐water medium. Attempts to extract growth inhibitors from filtrates of the fungal medium were unsuccessful. Indirect evidence suggested that perhaps the consumption of extracellular polysaccharide with concomitant release of organic acid by the fungus might be the factor inhibiting growth of Phormidium. Attempts to confirm experimentally the ecological significance for these biotic relationships are reported.