This paper deals mainly with the non-symbiotic
nitrogen-fixing bacteria other than B. Azotobacter
and B. saccharobutyricus. The two latter have
received a considerable amount of attention but
comparatively little work has been done on the less
active nitrogen -fixing bacteria of soils, especially
in recent years. An endeavour has been made to
isolate and stú.dy the aerobic bacteria which, in
addition to B. Azotobacter, probably play an importan
part in the fixation of elementary nitrogen in soils.
In view of the fact that practically no work has been
done on the nitrogen-fixing organisms of Egyptian .
soils, a complete study of representative samples of
the latter was also aimed at.
A number of investigations which dealt with many
of the organisms studied in the course of this work
have been previously carried out. The following is
a short review of the more important literature
concerned with non-symbiotic nitrogen -fixing bacteria
other than B. Azotobacter and the anaerobic forms.
B. aerogenes and similar organisms (Aerobacter,
B. aerobacter, B. acidi lactici, and B. pneumoniae)
have several times been found to be capable of
assimilating free nitrogen (15, 37, 42, L3, 39, 56),
and in experiments in which they were cultivated
along with other organisms results were also
obtained which pointed to their probable nitrogen-
fixing capacity (3, 14, 52). Other bacteria which
may belong to this group have been found to fix
nitrogen -(4, 31). In certain experiments strains
of B. aerogenes isolated from soil produced no
fixation of nitrogen (3, 56).
Strains of B. cloacae which were isolated from
soil have been found to be unable to fix nitrogen (56
B. ra_diobacter has proved to be a nitrogen-
fixing organism (15, 16, 22, 23, 24, 37, 380 142, 43,
49, 56), although certain negative or doubtful
findings have been recorded (3, 56, 61).
Of the three strains of the B. lactis innocuum
type isolated from soil, only two were found to be
capable of fixing nitrogen (43, 49).
Two strains of B. lactis viscosum from soils
brought about a small fixation of nitrogen (37, 38,
43, 49) .
A strain of B. prodigiosum from soil exhibited
the capacity of assimilating nitrogen (37). Another
positive result with the same organism, which,
however, was obtained under doubtful conditions,
has been recorded (25).
B. fluorescens and related types have been
found to fix nitrogen in certain experiments (1l, 22,
33), but not in others (37, L3, L.9).
Other short rods which have been found to be
capable of fixing nitrogen include B. turcosum (38,
)42), B. chrysogloea (22, 1!2), B. tartaricum (42),
B. Krakataui (28) , Pseud. leuconitrophilus (47),
B. alcaligenes (11), B. aurentiacus (11),B. candicans
(11), B. azophile (18), B. Truffauti (63) and B.
lipsiense (t2), although the fixation recorded in the
last case is doubtful.
Mic. sulfurens (112) and a similar unidentified
micrococcus (29) have shown the power to fix nitrogen
A considerable number of sporing rods have been
found to fix nitrogen. B. megatherium was able to
fix nitrogen in certain experiments (21, 59, 60,
62), but negative results have also been obtained
with this bacillus (56). B. Fllenbachensis has
shown the capacity to fix nitrogen (21) but several
negative results have also been obtained with this
organism (20, 27, 55).
Several other sporersin which the capacity to
assimilate nitrogen has been demonstrated include
B. mesentericus (3), B. asterosporus (8), B.
tumescens (11), B. ruminatus (11), B. oxalaticus (t2)
B. malabarensis (42), B. danicus (14)1, L5), and a
similar organism to the latter (24) and Planobacillus
nitrofigens (5).
A large number of bacteria which have not been
identified have been recorded as nitrogen -fixers
(13, 29, 34, 36, 48, 53).
Certain organisms have been recorded as having
fixed nitrogen in impure culture (2, 50).
A number of organisms have recently been
described (10) which produce an apparent fixation in
soil but practically all failed to do so in solution.
The following organisms have been found to' be
incapable of assimilating elementary nitrogen:
B. coli (43, 49, 56), B. agreste (37), Mic. pyogenes
(14.3, 49),B, subtilis (21, 42), although a fixation
by thé latter (255) has been obtained as a result
of an unsatisfactory experiment.
