326 MICEOBIOLOGY OF SOIL 



Relative Efficiency of Different Species. — In Marchal's experiments 

 already referred to, the species employed showed marked differences in 

 their ability to produce ammonia out of egg albumin. The following 

 proportions of the protein nitrogen were converted into ammonia in 

 twenty days: 



B. mycoides. .-. 46 per cent B. subtilis 23 per cent 



B. (Proteus) vulgaris 36 per cent B. janthinus 23 per cent 



B. mesentericus vulgatus.. 29 per cent B.fluorescens putidus 22 per cent 



Sarcina lutea 27 per cent B.fluorescens liquefaciens . 16 per cent 



Furthermore, apart from the variations from species to species, differ- 

 ences have been observed by Marchal and many other investigators 

 between one strain and another of any single species isolated from the 

 same or different soils. It must be remembered, therefore, that in the 

 study of ammonification in soils and culture solutions, due considera- 

 tion should be given to differences in physiological efficiency as they are 

 manifested by strains and species of microorganisms. 



Apart from the ammonifying bacteria already mentioned there is a 

 group of organisms studied by Miiller, Pasteur, van Tieghem, Leube, 

 Miquel, Beyerinck and others. These are the so-called urea bacteria, 

 capable of intensive transformation of urea and allied compounds into 

 ammonium carbonate, by means of the enzyme urease. 



CO + 2H2O = (NH4)2C03 



NH2 



Morphologically these organisms include spherical and rod forms, 

 spore-bearing and non-spore bearing species. Most of the urea bacteria 

 are particularly prominent in the transformation of animal manures. 



Ammofdfying Efficiency. — Lipman and Burgess have found marked 

 differences in the ammonifying efficiency of fifteen organisms in pure 

 cultures using peptone, bat guano, sheep' and goat manure, dried 

 blood, tankage, cottonseed meal and fish guano. The nature of the 

 soil as well as the nature of the nitrogenous material markedly modify 

 an organism's ammonifying power. B. tumescens on the whole appears to 

 have been the most efficient organism tested. Comparing these findings 



