Various bacteria, actinomycetes, fungi, and bacteriophages were exposed to microwaves of 2,450 + 20 MHz in the presence and in the absence of water. It was found that microorganisms were inactivated only when in the presence of water and that dry or lyophilized organisms were not affected even by extended exposures. The data presented here prove that microorganisms are killed by "thermal effect" only and that, most likely, there is no "nonthermal effect"; cell constituents other than water do not absorb sufficient energy to kill microbial cells.

FIG. 4. Mixture of unstained Escherichia coli (arrow 1), unstained Sarcina lutea (arrow 2), and stained Bacillus globigii spores (arrows S and 4). Immunofluorescence of B. globigii spores was taken in this background. antigen were kindly supplied by the Biological Laboratories of the U.S. Army Chemical Corps.

Azotobacter vinelandii cells grew well in a medium made from soil and distilled water which contained little or no carbohydrate. They utilized p-hydroxybenzoic acid and other phenolic acids, soil nitrogen, and water-soluble mineral substances. Seventeen soils which supported excellent growth of A. vinelandii contained 11 to 18 different phenolic acids each, including p-hydroxybenzoic, m-hydroxybenzoic, vanillic, p-coumeric, syringic, cisand trans-ferrulic, and other unidentified aromatic acids. Three white, chalky "caliche" soils which were taken from areas where no plants grew failed to support the growth of A. vinelandii, and these contained no, two, and three phenolic acids, respectively. A. vinelandii did not fix nitrogen when growing in dialysates of soils which contained numerous phenolic acids. Growth was ample and rapid in most of the soils tested, but cell morphology was different from that usually seen in chemically defined, nitrogen-free media which contain glucose.

SUMMARYThe growth of several selected micro-organisms in rapidly dividing cultures of Chlorella pyrenoidosa T X 71105 was studied. Bacterial proliferation was a function of algal growth and bacterial growth occurred, at least in part, as a result of the excretion of organic substances into the culture medium by rapidly dividing algae. These substances capable of supporting bacterial oxidation and growth were varied in kind and were utilized selectively by the different bacteria. Only a small fraction of the soil and air bacteria grew in the algal cultures. The majority of soil and air bacteria survived in mixed culture for several days but did not increase in numbers. On the other hand, 6 out of 8 bacteria pathogenic for man died promptly in cultures of Chlorella pyrenoidosa ; but Salmonella typhi and S . puratyphi grew well for extended periods of time. Fungi capable of producing macrocolonies on potato glucose agar at pH 3.5 did not increase in numbers during 8 days. Yeasts and actinomycetes were not detected by the methods used; bacteriophages were observed with some regularity .