PATHOGENIC SPECIES 689 



rule out the possibility that foam at permissive temperatures 

 supports some growth of D. gallopaua. The foam has a high 

 concentration of organic carbon in comparison with the water, which 

 contains less than 5 ppm (Fhermans, unpublished data), and might 

 support growth (Table 2). Bacteria are abundant in foam (e.g., 

 1.89 X 10^ cells/ml of condensed foam on 50°C water, measured 

 directly in a counting chamber); motile and dividing cells of bacteria 

 are abundant. Germinating conidia of D. gallopaua, microcolonies, 

 and sporulation were not seen in condensed foam, however. These 

 indicators of growth were readily apparent in condensed foam taken 

 from hot-spring effluents in Wyoming (Tansey and Brock, 1973, and 

 unpublished data). Furthermore, new foam contains CFU's of D. 

 gallopaua which could not have formed in the few minutes that foam 

 existed (Table 4). FoEim is dynamic; individual patches form and 

 disappear in the course of a few minutes or hours. Colony forming 

 units of D. gallopaua also occur in places where foam cannot 

 accumulate because the mat is well above rapidly flowing water in 

 smooth-walled canals (Table 4). 



The photoautotrophic species component of the water-edge 

 microbial mat varies with temperature. At 45°C, it is Mastigocladus 

 laminosus and Oscillatoria species. 



Our data support the conclusion that fungi have not adapted to 

 thermal stress in ways that result in populations of aquatic species 

 comparable to those of prokaryotic microorganisms. No known 

 species of aquatic fungi can grow at 50° C. 



ACKIMOWLEDGMEIMTS 



The research reported here was developed during the course of 

 work under contract No. AT(07-2)-l with the U. S. Department of 

 Energy. 



We thank I. L. Sauls, J. L. Todd, and A. B. Parrott for technical 

 assistance. 



REFERENCES 



Ajello, L., and L. C. Runyon, 1953, Infection of Mice with Single Spores of 

 Histoplasma capsulatum, J. BacterioL, 66: 34-40. 



American Public Health Association, 1976, Standard Methods for the Examina- 

 tion of Water and Waste Water, 14th ed., pp. 982-986, Washington, D. C. 



Belly, R. T., M. R. Tansey, and T. D. Brock, 1973, Algal Excretion of 

 *'*C-Labeled Compounds and Microbial Interactions in Cyanidiitm caldarium 

 Mats, J. PhycoL, 9: 123-127. 



