the gene coding for the receptor (Churchill and Chen 2011). This suggests that these
bacteria do not send the command but rather respond to the one sent from other
species.
The occurrence of a different mode of interspecies communication can be
deduced from the activity of Streptomyces metabolites. As mentioned previously,
this group of soil bacteria produces a great variety of secondary metabolites
exhibiting antibiotic activity. However, Streptomyces species also produce substances that assist the growth of other organisms. One such substance is cobalamin
(vitamin B12), which is a cobalt-containing tetrapyrolle that serves as an essential
cofactor for several enzymes, such as methyltransferases (Sokolovskaya et al. 2020).
Despite its essential role in a wide range of organisms, including mammals, the
ability to synthesize this cofactor is distributed only among some prokaryotes. This
indicates that prokaryotic cobalamin producers support the life of a vast variety of
living organisms. Evidence from classic screening studies suggests that Streptomyces and related bacteria are effective suppliers of cobalamin.
Another example of Streptomyces-derived products of public benefit are
desferrioxamines, which belong to a group of iron-chelating cage compounds termed
siderophores (Yamanaka et al. 2005). The ferric iron-bound form of desferrioxamine
is incorporated into the cell via a specific translocator protein and supplies ferric iron
to ferric-dependent cellular functions. While the ability to synthesize
desferrioxamines is specifically distributed to Streptomyces and some other bacterial
groups, genes encoding membrane translocator proteins are widely distributed even
among those lacking the ability to synthesize the compound. The latter group of
organisms probably utilizes the siderophores produced by the formerly mentioned
supplier group of bacteria.
25.2.2.5 Communication via Non-Specific Metabolites
Microbial interaction is mediated not only by specific bioproducts but also by
non-specific ones. For example, classic works on diverged microorganisms demonstrated that CO 2 triggers their change into growth mode (Ueda and Beppu 2016). In
Streptomyces and Clostridium, high CO 2 levels induce spore germination. In Mucor,
pseudohyphal growth is activated in a high CO 2 atmosphere. Some bacteria require
elevated CO 2 for their growth. Genetic evidence displayed in some model microorganisms has revealed that such high CO 2 -dependent growth occurs in knockout
mutants for carbonic anhydrase (Ueda and Beppu 2016). The enzyme carbonic
anhydrase catalyzes the interconversion between CO 2 and bicarbonate (HCO 3
À )
and is hence supposed to have a role in supplying bicarbonate to bicarbonatedependent enzymes, such as acetyl-CoA carboxylase and carbamoyl-phosphate
synthase that respectively are essential for the synthesis of fatty acids and nucleotides. Bacteria-lacking carbonic anhydrase cannot grow under normal atmospheric
conditions but can grow in a high CO 2 atmosphere by consuming bicarbonate
generated from CO 2 by natural equilibrium.
534
K. Ueda
bacteria do not send the command but rather respond to the one sent from other
species.
The occurrence of a different mode of interspecies communication can be
deduced from the activity of Streptomyces metabolites. As mentioned previously,
this group of soil bacteria produces a great variety of secondary metabolites
exhibiting antibiotic activity. However, Streptomyces species also produce substances that assist the growth of other organisms. One such substance is cobalamin
(vitamin B12), which is a cobalt-containing tetrapyrolle that serves as an essential
cofactor for several enzymes, such as methyltransferases (Sokolovskaya et al. 2020).
Despite its essential role in a wide range of organisms, including mammals, the
ability to synthesize this cofactor is distributed only among some prokaryotes. This
indicates that prokaryotic cobalamin producers support the life of a vast variety of
living organisms. Evidence from classic screening studies suggests that Streptomyces and related bacteria are effective suppliers of cobalamin.
Another example of Streptomyces-derived products of public benefit are
desferrioxamines, which belong to a group of iron-chelating cage compounds termed
siderophores (Yamanaka et al. 2005). The ferric iron-bound form of desferrioxamine
is incorporated into the cell via a specific translocator protein and supplies ferric iron
to ferric-dependent cellular functions. While the ability to synthesize
desferrioxamines is specifically distributed to Streptomyces and some other bacterial
groups, genes encoding membrane translocator proteins are widely distributed even
among those lacking the ability to synthesize the compound. The latter group of
organisms probably utilizes the siderophores produced by the formerly mentioned
supplier group of bacteria.
25.2.2.5 Communication via Non-Specific Metabolites
Microbial interaction is mediated not only by specific bioproducts but also by
non-specific ones. For example, classic works on diverged microorganisms demonstrated that CO 2 triggers their change into growth mode (Ueda and Beppu 2016). In
Streptomyces and Clostridium, high CO 2 levels induce spore germination. In Mucor,
pseudohyphal growth is activated in a high CO 2 atmosphere. Some bacteria require
elevated CO 2 for their growth. Genetic evidence displayed in some model microorganisms has revealed that such high CO 2 -dependent growth occurs in knockout
mutants for carbonic anhydrase (Ueda and Beppu 2016). The enzyme carbonic
anhydrase catalyzes the interconversion between CO 2 and bicarbonate (HCO 3
À )
and is hence supposed to have a role in supplying bicarbonate to bicarbonatedependent enzymes, such as acetyl-CoA carboxylase and carbamoyl-phosphate
synthase that respectively are essential for the synthesis of fatty acids and nucleotides. Bacteria-lacking carbonic anhydrase cannot grow under normal atmospheric
conditions but can grow in a high CO 2 atmosphere by consuming bicarbonate
generated from CO 2 by natural equilibrium.
534
K. Ueda