ANNUAL REPORT, 1934 21 



DEPARTMENT OF BACTERIOLOGY 

 Leon A. Bradley in Charge 



The Azotobacter Soil Plaque Test for Determining Soil Nutrient Deficiencies. 



(James E. Fuller.) This was a continuation of an investigation previously re- 

 ported (Mass. Agr. Expt. Sta. Bui. 305, p. 15, 1933). The technique of Sackett 

 (Colo. Agr. Expt. Sta. Bui. 375, 1931) was employed in setting up the soil plaque 

 tests. Because the presence of Azotobacter in the soils tested could not be de- 

 pended on, all plaques were inoculated with Azotobacter. In addition all plaques 

 were treated with calcium carbonate, and mannite was used as a source of energy. 

 Chemical tests for available phosphorus were made according to the technique 

 of Truog (Jour. Amer. Soc. Agron. 22:874, 1930). The soils examined were from 

 ten of the college farm and experiment station plots and from three private garden 

 plots. The soil plaque tests indicated that all of the soils were deficient in available 

 phosphorus, in spite of the fact that all of the plots represented produced satis- 

 factory crops. The Truog tests revealed a rather wide variation, but no actual 

 deficiency in the available phosphorus of the soils. The study indicated that the 

 Azotobacter soil plaque test is not a dependable indicator of the available phos- 

 phorus content of the rather acid sandy loam soil which is common in this region. 

 Our results agreed with those published by Walker and associates (Jour. Amer. 

 Soc. Agron. 22:642, 1930). Details and data will be furnished on request. 



Calcium Metabolism of Nitrogen-Fixing Bacteria. (James E. Fuller.) This 

 study was undertaken on the premise that calcium might exert some stimulating 

 influence, aside from the neutralization of acids, on the metabolism of Azoto- 

 bacter. Twelve strains of Azotobacter, freshly isolated from soil at the beginning 

 of the experiment, were cultivated on a medium free from calcium (the medium 

 was composed of K 2 HP0 4 , mannite, and distilled water). Nitrogen-fixation 

 on the medium was determined and compared with nitrogen-fixation on the 

 same medium to which varying quantities of calcium carbonate were added. 

 As much nitrogen was fixed on the calcium-free medium as in the presence of 

 any of the quantities of calcium carbonate, and as the concentration of calcium 

 carbonate was increased the amount of nitrogen fixed was apparently decreased. 

 Cultures grown on Ashby's medium gave the smallest amount of nitrogen fixed 

 in the study. The twelve Azotobacter strains, after being cultivated for two 

 years on the calcium-free medium, appeared to have unimpaired nitrogen-fixing 

 power. Results were the opposite of those anticipated, and lime appeared to be 

 unimportant in the nitrogen-fixing metabolism of the organism. The medium 

 employed contained no demonstrable calcium except that purposely added. 



The Influence of Bile and Bile Salts on Bacterium Aerogenes. (James E. 

 Fuller.) The purpose of this study is to investigate the possibility that Bacterium- 

 aero genes, generally regarded as a non-fecal organism, may acquire characteristics 

 of Bacterium coli of fecal origin. Twenty-five strains of Bacterium aerogenes iso- 

 lated from water were chosen. These strains were proved, by repeated tests, to 

 be negative for the methyl red test and positive for the Voges-Proskauer, sodium 

 citrate, and uric acid tests. These strains have been cultivated for three months 

 in a fluid medium composed of one percent each of Difco peptone, Difco lactose, 

 and K 2 HP0 4 ,in distilled water. The strains were set up in three series of cultures: 

 to one was added one percent of sodium taurocholate; to another one percent of 

 sodium glycocholate; and to the third one percent of ox bile. Incubating tempera- 

 ture was 37°C. Cultures were transferred once each week, and once each month 



