Beijerinck believed that the metamorphosed Bacillus Radicicola bacteria present
in the bacteroids hence had lost their ability to develop aside from serving their
function as shaped protein bodies. Those metamorphic bacteria seemed linked to the
normal, culturable form of Bacillus Radicicola which he commonly found in soil.
Beijerinck mentioned four characteristics about the root nodules that he studied:
First—the nodules seemed to go through two phases, development and exhaustion;
Second—during development, the bacteria that have entered the cells are more or
less completely enclosed by the protoplasm, gradually lose their vegetative
power, and finally change into bacteroids which are unable to grow. Those
bacteria which were present in the nodules but not included in the cell cytoplasm,
on the other hand, remained capable of growth (he used the terms cytoplasm and
protoplasm interchangeably although we now, 110 years later, sometimes make a
distinction between those two words);
Third, exhaustion can take place in two ways: it can be based either on a normal
drainage process by the plant, which seemed to be exhaustion of the nodule, or on
bacterial overgrowth. During normal emptying of the nodule, the bacteroids
seemed to leave behind either some peculiar strongly light-refractive bacteroidlike remains, or some microsome-shaped bodies which like the bacteroids themselves are unable to grow. In bacterial exhaustion, on the other hand, there was an
overgrowing by countless easily cultivated individuals of Bacillus Radicicola still
present within the nodules in addition to the plant cells containing vesicular
bacteroids that were unable to grow or develop;
Fourth—development of the nodules can stop at all stages, they eventually either
come to a state of rest or fail due to exhaustion. Beijerinck noticed that other
bacteria existed in healthy and also decaying root nodules. Another one of the
organisms which he identified was Bacillus fluorescens putidus which now is
named Pseudomonas putida.
Beyerinck said that, although the nodules cannot be understood in the same sense
as are normal plant organs such as roots, stems, and leaves, existence of the nodules
shows such an analogy that it appeared certain the nodules represented a nutritional
function for the benefit of the plant. He included the surmise that, regardless of their
numerous associated disorders and some noted exceptions, emptying of the protein
supply from the bacteroids must be regarded as representing a normal life cycle of
the nodules for at least herbacaous plants.
Beyerinck proposed that the question should be, is it permissible to conclude
from the foregoing findings that the nodules are completely useless for the bacteria?
He believed that such a view is not correct and that, at least in certain cases, life in the
nodules primarily benefits the bacteria. Beyerinck observed that the nodule plasma
clearly produces proteins but Beyerinck could not get his isolated and aerobically
growing bacteria to produce nitrogenous compounds. It was only later understood
that the enzyme complex responsible for nitrogen reduction, termed nitrogenase, is
inactivated by oxygen. Therefore, the process of nitrogen fixation requires conditions that are either anoxic or nearly anoxic and his presumption of their being lower
oxygen tension within the nodules clearly was correct. In symbiotic associations, the
14 Discovering the Symbiotic Nature of Microbial Life: Summarizing Milestone. . .
229
in the bacteroids hence had lost their ability to develop aside from serving their
function as shaped protein bodies. Those metamorphic bacteria seemed linked to the
normal, culturable form of Bacillus Radicicola which he commonly found in soil.
Beijerinck mentioned four characteristics about the root nodules that he studied:
First—the nodules seemed to go through two phases, development and exhaustion;
Second—during development, the bacteria that have entered the cells are more or
less completely enclosed by the protoplasm, gradually lose their vegetative
power, and finally change into bacteroids which are unable to grow. Those
bacteria which were present in the nodules but not included in the cell cytoplasm,
on the other hand, remained capable of growth (he used the terms cytoplasm and
protoplasm interchangeably although we now, 110 years later, sometimes make a
distinction between those two words);
Third, exhaustion can take place in two ways: it can be based either on a normal
drainage process by the plant, which seemed to be exhaustion of the nodule, or on
bacterial overgrowth. During normal emptying of the nodule, the bacteroids
seemed to leave behind either some peculiar strongly light-refractive bacteroidlike remains, or some microsome-shaped bodies which like the bacteroids themselves are unable to grow. In bacterial exhaustion, on the other hand, there was an
overgrowing by countless easily cultivated individuals of Bacillus Radicicola still
present within the nodules in addition to the plant cells containing vesicular
bacteroids that were unable to grow or develop;
Fourth—development of the nodules can stop at all stages, they eventually either
come to a state of rest or fail due to exhaustion. Beijerinck noticed that other
bacteria existed in healthy and also decaying root nodules. Another one of the
organisms which he identified was Bacillus fluorescens putidus which now is
named Pseudomonas putida.
Beyerinck said that, although the nodules cannot be understood in the same sense
as are normal plant organs such as roots, stems, and leaves, existence of the nodules
shows such an analogy that it appeared certain the nodules represented a nutritional
function for the benefit of the plant. He included the surmise that, regardless of their
numerous associated disorders and some noted exceptions, emptying of the protein
supply from the bacteroids must be regarded as representing a normal life cycle of
the nodules for at least herbacaous plants.
Beyerinck proposed that the question should be, is it permissible to conclude
from the foregoing findings that the nodules are completely useless for the bacteria?
He believed that such a view is not correct and that, at least in certain cases, life in the
nodules primarily benefits the bacteria. Beyerinck observed that the nodule plasma
clearly produces proteins but Beyerinck could not get his isolated and aerobically
growing bacteria to produce nitrogenous compounds. It was only later understood
that the enzyme complex responsible for nitrogen reduction, termed nitrogenase, is
inactivated by oxygen. Therefore, the process of nitrogen fixation requires conditions that are either anoxic or nearly anoxic and his presumption of their being lower
oxygen tension within the nodules clearly was correct. In symbiotic associations, the
14 Discovering the Symbiotic Nature of Microbial Life: Summarizing Milestone. . .
229