nitrogen fixing microbes are sequestered in differentiated cells which limit exposure
of the nitrogenase to oxygen.
We now know Beijerinck’s discovered bacteria to be members of the genus
Rhizobium, class Alphaproteobacteria. The rhizobia are soil bacteria that form an
endosymbiotic nitrogen-fixing association with the roots of legumes, and additionally with some other plants. Beijerinck mentioned in his publication Melampyrum
pratense and Rhinanthus major, which are members of the family Orobanchaceae
and do not seem to form root nodules. He did not mention the plant genus
Parasponia, which belongs to the family Cannabaceae and does develop Rhizobium
root nodules.
Beijerinck proposed, as per my translation, “Why, we continue to ask, did the
Papilionaceae use the root bacteria to create protein stores? Don’t they show in their
seeds that they can achieve this purpose even without bacteria?” and, “For the time
being we take the protein supply of the bacteroids as a given, but we will come back
to its origin at the end and only then can we fully indicate the probable meaning of
the nodules.”
14.13 “Symbiosis” by Marshall Ward, 1899
Harry Marshall Ward (1899b) wanted to distinguish differences between parasitism
and symbiosis. He suggested that symbiosis could be considered in a broad sense,
and should not be used to describe interactions between species that only represented
either temporary associations or transient encounters. In his words “When we come
to inquire as to the processes which lead to enhancement of the functional activity of
one organism by another living symbiotically with it ...” And, he talked about
symbiosis as including associations in which neither species could survive alone.
Ward included in his presentation the importance of nitrogen fixation and nitrogen cycling. Among his examples were the fungal symbiosis of mycorrhiza and the
roots of plants, plus the bacterial nitrogen fixation associated with leguminous
nodules that was achieved by “Hellriegel and Willfarth’s cultures” which we know
to be effected by Rhizobium. Ward included the nitrogen cycling which occurs when
Bacillus ramosus, which we now call Erysipelatoclostridium ramosum, is added
together with Nitrosomonas and Nitrobacter.
Wards review included several photosynthetic symbioses. Among his examples
were the formation of lichens, which are composite organisms that exist as a
mutualistic relationship between either an algae or a cyanobacteria living among
the filaments of fungi. Ward also mentioned microbial symbioses in the plant world
including among those the photosynthetic symbionts which were then termed algae
but we now know as cyanobacteria, which live intracellularly within the stems of
Gunnera, in the roots of Cycads, and either within or on the thallus of Anthoceros
(hornworts), Blasia (liverwort), Azolla (mosquito ferns), and Lemna (duck weed).
The cyanobacteria in those partnerships provide fixed nitrogen to the plant, while the
plant provides fixed carbon for the cyanobacteria.
230
C. J. Hurst
of the nitrogenase to oxygen.
We now know Beijerinck’s discovered bacteria to be members of the genus
Rhizobium, class Alphaproteobacteria. The rhizobia are soil bacteria that form an
endosymbiotic nitrogen-fixing association with the roots of legumes, and additionally with some other plants. Beijerinck mentioned in his publication Melampyrum
pratense and Rhinanthus major, which are members of the family Orobanchaceae
and do not seem to form root nodules. He did not mention the plant genus
Parasponia, which belongs to the family Cannabaceae and does develop Rhizobium
root nodules.
Beijerinck proposed, as per my translation, “Why, we continue to ask, did the
Papilionaceae use the root bacteria to create protein stores? Don’t they show in their
seeds that they can achieve this purpose even without bacteria?” and, “For the time
being we take the protein supply of the bacteroids as a given, but we will come back
to its origin at the end and only then can we fully indicate the probable meaning of
the nodules.”
14.13 “Symbiosis” by Marshall Ward, 1899
Harry Marshall Ward (1899b) wanted to distinguish differences between parasitism
and symbiosis. He suggested that symbiosis could be considered in a broad sense,
and should not be used to describe interactions between species that only represented
either temporary associations or transient encounters. In his words “When we come
to inquire as to the processes which lead to enhancement of the functional activity of
one organism by another living symbiotically with it ...” And, he talked about
symbiosis as including associations in which neither species could survive alone.
Ward included in his presentation the importance of nitrogen fixation and nitrogen cycling. Among his examples were the fungal symbiosis of mycorrhiza and the
roots of plants, plus the bacterial nitrogen fixation associated with leguminous
nodules that was achieved by “Hellriegel and Willfarth’s cultures” which we know
to be effected by Rhizobium. Ward included the nitrogen cycling which occurs when
Bacillus ramosus, which we now call Erysipelatoclostridium ramosum, is added
together with Nitrosomonas and Nitrobacter.
Wards review included several photosynthetic symbioses. Among his examples
were the formation of lichens, which are composite organisms that exist as a
mutualistic relationship between either an algae or a cyanobacteria living among
the filaments of fungi. Ward also mentioned microbial symbioses in the plant world
including among those the photosynthetic symbionts which were then termed algae
but we now know as cyanobacteria, which live intracellularly within the stems of
Gunnera, in the roots of Cycads, and either within or on the thallus of Anthoceros
(hornworts), Blasia (liverwort), Azolla (mosquito ferns), and Lemna (duck weed).
The cyanobacteria in those partnerships provide fixed nitrogen to the plant, while the
plant provides fixed carbon for the cyanobacteria.
230
C. J. Hurst