CONTRIBUTION TO THE CHEMISTRY OF DECOMPOSI¬ 
TION OF PROTEINS AND AMINO ACIDS BY VARIOUS 
GROUPS OF MICROORGANISMS 1 
By Selman A. Waksman and S. Lomanitz 
New Jersey Agricultural Experiment Station 
INTRODUCTION 
Extensive work has been done on 
the decomposition of proteins and their 
derivatives by microorganisms, especi¬ 
ally by bacteria and fungi. In the 
great majority of cases one of the final 
products, ammonia, has been used as 
a criterion for the course and rapidity 
of this decomposition; witness only the 
large number of contributions to the 
so-called “ammonification” studies, 
both by crude and by pure cultures of 
microorganisms, in investigations deal¬ 
ing with soil microbiology. Whenever 
bacterial metabolism has been studied, 
especially nitrogenous metabolism, am¬ 
monia has usually been the product to 
be measured, some authorities laying 
more emphasis upon this as an index of 
bacterial decomposition of proteins ( 12 ) 2 
and some less ( 5 ). Very little atten¬ 
tion has ordinarily been paid to the 
transformation of the carbon part of 
the protein molecule or to the trans¬ 
formation of the available carbon pres¬ 
ent in the medium, in addition to that 
of the protein molecule; at least not to 
such an extent as to indicate the im¬ 
portance which this transformation 
plays, not only in connection with the 
formation or accumulation of am¬ 
monia, but with the decomposition of 
the protein molecule. 
The purpose of this contribution is 
to indicate how the structure of the 
particular amino acids and of various 
proteins consisting of different amino 
acid groupings influences the mecha¬ 
nism of their decomposition by repre¬ 
sentatives of the three different groups 
of microorganisms, which play an im¬ 
portant part in the decomposition of 
proteins in nature—the bacteria, 
actinomycetes, and fungi or molds. 
LITERATURE 
The three methods most commonly 
used for measuring the rapidity and 
amount of decomposition of proteins 
can be summarized as follows: 
. Disappearance of original protein, as 
in the liquefaction of gelatin, coagulation 
and liquefaction of milk casein, zone for¬ 
mation on casein agar plate, etc .-—Very 
little attention has been paid, however, 
to the actual determination, in an ac¬ 
curate quantitative manner, of the 
amounts of protein decomposed. Even 
the numerous gelatin liquefaction studies 
are more qualitative than quantitative 
in nature. An approach has been made 
to quantitative methods only by the in¬ 
troduction of measurements of viscosity 
in the study of gelatin liquefaction (30); 
but even here, no differentiation has as 
yet been made between the mere change 
in the physical condition of the gela¬ 
tin and its actual chemical hydrolysis, 
since liquefaction of gelatin may be 
brought about by enzymes (gelatin- 
ases), and this action may be entirely 
independent of proteolytic activity. 
Berman and Rettger (1) pointed out 
that the ability of an organism to 
liquefy gelatin is no sure indication of 
its proteolytic properties. 
Formation of intermediary products 
in the decomposition of proteins, chiefly 
amino compounds .—Berman and Rett¬ 
ger (1) used the biuret test for fol¬ 
lowing the course of protein hydrol¬ 
ysis. Sears (25), Waksman (S3), and 
others used the Van Slyke method for 
determining the amino acid nitrogen 
as a method for following the course 
of decomposition of proteins. Itano 
(9), Kendall (13), Berman and Rettger 
(1) and others used the Sorensen (26) 
formol titration method; while DeBord 
(5) used the Folin (8) method for de¬ 
termining amino nitrogen. The de¬ 
termination of amino nitrogen as an 
index of decomposition of proteins 
should be used, however, only when the 
particular processes carried on by the 
different organisms are properly under¬ 
stood. When the protein is present 
as the only source of carbon and nitro¬ 
gen in the medium and has to be used 
by the pure or mixed culture, as a 
source of both nitrogen and energy, 
the fact that the mere hydrolysis of 
1 Received for publication May 1,1924; issued April 1925. Paper No. 167 of the Journal Series, New 
Jersey Agricultural Experiment Station, Department of Soil Chemistry and Bacteriology. 
s Reference is made by number (italic) to “Literature cited,” p. 280. 
Journal of Agricultural Research, 
Washington, D. C. 
( 263 ) 
Vol. XXX, No. 3 
Feb. 1, 1925 
Key No. N. J. 13 
