decarboxylation, it cannot produce putrescine without the help of the other bacterial
population.
Another well-known example of syntrophy was published in 1939 by Horace
Albert Barker. Barker isolated an organism which he named Methanobacillus
omelianskii. It appeared that microorganisms alone could use ethanol and carbon
dioxide to produce acetate plus methane. Thermodynamically, the reaction is feasible. However, later it turned out that these reactions are in fact carried out by two
kinds of organisms. Acetobacterium woodii forms hydrogen and acetate from
ethanol. The other microbe is Methanobacterium bryantii, which uses hydrogen
and carbon dioxide (but no ethanol) to make methane. These two microbes were
originally isolated and stored together. That also suggests a close (somatic, physical)
relationship between the two partners. Another example is the syntrophic oxidation
of butyrate. The overall reaction of butyrate to methane and carbon dioxide is this:
2 CH 3 CH 2 CH 2 COOH þ 2 H þ 2 H 2 O ¼ 5 CH 4 þ 3 CO 2 :
Under standard conditions, the above reaction produces free energy, 177 kJ/2
mols butyrate. This reaction is catalyzed in microbial culture by three different, but
mutually cooperating kinds of bacteria. First, one kind of bacterium transforms
butyrate into acetate and hydrogen. Then another bacterial species produces methane
from hydrogen and carbon dioxide. In the end, the acetate is transformed into
methane and carbon dioxide by a third bacterial species. Another syntrophic oxidation of acetate, producing methane plus carbon dioxide, already had been reported in
1936 (Barker 1936).
15.1.2 Commensalism
The word commensal is derived from Latin “com” ¼ simultaneously and “mensa” ¼
table, also meaning meal. The word, introduced by Edouard Van Beneden, could be
also interpreted as “sharing the table.” Commensalism denotes interaction, or coexistence, of two or more organisms. One of them is the commensal, i.e., the one which
benefits from this relationship. The host, which oftentimes is a macroorganism, is not
in any way harmed or negatively influenced. In nature, there exist different forms of
commensalism, ranging from loose relationships to more lasting and stronger ones.
In the case of stronger relationships, the commensal is located in an immediate
vicinity of the host, perhaps even on its body surface or in body cavities. Typical
human commensals are some species of coliform bacteria in the gastrointestinal
tract. Similar situations exist in animals. The microflora of the mouth or the skin can
serve as another example. Based on the type of commensalism, participant microorganisms can be divided into ectocommensals and endocommensals.
Ectocommensals live on plant surfaces, but mostly on animals and other organisms. There exist also microscopic commensals that live on the surface of microorganisms. The host organisms provide nutrition to the ectocommensals in the form of
15 Microscopic World and the Phenomenon of Symbiosis in the Natural Environment
245
population.
Another well-known example of syntrophy was published in 1939 by Horace
Albert Barker. Barker isolated an organism which he named Methanobacillus
omelianskii. It appeared that microorganisms alone could use ethanol and carbon
dioxide to produce acetate plus methane. Thermodynamically, the reaction is feasible. However, later it turned out that these reactions are in fact carried out by two
kinds of organisms. Acetobacterium woodii forms hydrogen and acetate from
ethanol. The other microbe is Methanobacterium bryantii, which uses hydrogen
and carbon dioxide (but no ethanol) to make methane. These two microbes were
originally isolated and stored together. That also suggests a close (somatic, physical)
relationship between the two partners. Another example is the syntrophic oxidation
of butyrate. The overall reaction of butyrate to methane and carbon dioxide is this:
2 CH 3 CH 2 CH 2 COOH þ 2 H þ 2 H 2 O ¼ 5 CH 4 þ 3 CO 2 :
Under standard conditions, the above reaction produces free energy, 177 kJ/2
mols butyrate. This reaction is catalyzed in microbial culture by three different, but
mutually cooperating kinds of bacteria. First, one kind of bacterium transforms
butyrate into acetate and hydrogen. Then another bacterial species produces methane
from hydrogen and carbon dioxide. In the end, the acetate is transformed into
methane and carbon dioxide by a third bacterial species. Another syntrophic oxidation of acetate, producing methane plus carbon dioxide, already had been reported in
1936 (Barker 1936).
15.1.2 Commensalism
The word commensal is derived from Latin “com” ¼ simultaneously and “mensa” ¼
table, also meaning meal. The word, introduced by Edouard Van Beneden, could be
also interpreted as “sharing the table.” Commensalism denotes interaction, or coexistence, of two or more organisms. One of them is the commensal, i.e., the one which
benefits from this relationship. The host, which oftentimes is a macroorganism, is not
in any way harmed or negatively influenced. In nature, there exist different forms of
commensalism, ranging from loose relationships to more lasting and stronger ones.
In the case of stronger relationships, the commensal is located in an immediate
vicinity of the host, perhaps even on its body surface or in body cavities. Typical
human commensals are some species of coliform bacteria in the gastrointestinal
tract. Similar situations exist in animals. The microflora of the mouth or the skin can
serve as another example. Based on the type of commensalism, participant microorganisms can be divided into ectocommensals and endocommensals.
Ectocommensals live on plant surfaces, but mostly on animals and other organisms. There exist also microscopic commensals that live on the surface of microorganisms. The host organisms provide nutrition to the ectocommensals in the form of
15 Microscopic World and the Phenomenon of Symbiosis in the Natural Environment
245