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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 1151

J.G. Kuenen, J. Boonstra, H.G.J. Schroder, and H. Veldkamp; Competition for inorganic substrates among chemoorganotrophic and chemolithotrophic bacteria. Microbial Ecology 3:119-130, 1977

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In aerobic enrichment experiments with a chemostat, using phosphate-limited lactate medium a Spirillum sp. predominated at the lower range of dilution rates. At the higher dilution rates an (chemoorganotrophic) unidentified rod-shaped bacterium came to the fore. The same result was obtained in competition experiments with pure cultures of the two bacteria. Growth parameters were: Rod, u(max)=0.48 hr-1, Ks(PO4(3-))=6.6x10E-8 M ; Spirillum, u(max)=0.24 hr-1, Ks(PO4(3-))=2.7x10E-8 M. The Spirillum grew faster than the rod at low dilution rates, not only under phosphate-limitation but also in K+, Mg2+, NH4+, aspartate-, succinate-, and lactate-limited cultures. Both organisms showed little substrate specificity and could utilize a similar carbon and energy sources. The results support the view of that part of the diversity among the bacteria in the natural environment is based on selection toward substrates concentration. Another set of competition experiments was carried out with pure cultures or two marine obligately chemolithotrophic colorless sulfer bacteria, Thiobacillus thioparus and Thiomicrospira pelophila. Tms. pelophila outgrew T. thioparus at low dilution rates under iron limitation, while the reserve was true at high dilution rates. It is concluded that the relatively fast growth of Tms. pelophila at low iron concentration may explain its higher sulfide tolerance. Organisms showing a selection advantage at very low concentration of limiting substrates appear to have a relatively surface to volume ratio.