concentrations and subsequent induction of specific gene expression. This cell
density-dependent control of the bacterial community is termed quorum sensing.
Another group of autoregulatory molecules precisely characterized for their
actions are the gamma-butyrolactones (GBLs) produced by Streptomyces species
(Horinouchi et al. 2010). Despite being prokaryotes, Streptomyces and related
bacteria exhibit a complex life cycle resembling that of filamentous fungi. In the
vegetative growth phase, the organism extends the projecting “substrate mycelium”—those mycelia that maintain contact with the substrate being used to sustain
the fungus. Then, the substrate mycelium forms an aerial mycelium, which culminates in a spore chain. The cellular development from substrate to aerial mycelium is
genetically linked to the production of secondary metabolites, including those that
have antibiotic activity. In this life cycle, GBLs serve as a switch for the initiation of
secondary metabolism and cell differentiation during the change from producing
substrate to aerial mycelium. Probably, GBL-mediated signaling causes the cells
within a colony to synchronize and simultaneously initiate drastic cellular development. Without such harmonization, antibiotics produced by some cells may kill
others. In the case of streptomycin whose production is controlled by a GBL called
A-factor, the self-resistance gene located in the center of the biosynthetic gene
cluster is induced prior to the expression of the adjacent biosynthetic genes.
[I would guess the rest of a fungal colony intrinsically is resistant to its selfproduced antifungal agents unless resistance to its own antimicrobial compounds
must be induced].
In addition to lactones, structurally diverged small molecules, including those
with peptidic and furanosyl backbones, are known to direct social behavior
of specific groups of bacteria (Horinouchi et al. 2010). The original identification
of these cell-cell signaling molecules occurred in a study focusing on the expression
of a specific phenotype, such as antibiotic production and biofilm formation in a
given bacterial species, which is clearly observed in laboratory conditions. This, in
turn, suggests that similar communication to control microbial functions or phenotypes invisible to researchers using conventional manipulation techniques likely also
exists in other microbial groups but remains unknown.
25.2.2.4 Interspecies Communication
The above mentioned lactone signals retain structural divergence in terms of their
alkyl side chains. The strict ligand selectivity of its cognate receptor distinguishes
the true signal from other structurally similar derivatives, thus establishing speciesspecific communication. On the other hand, some strains or species share an autoinducer of identical chemical structure. In such a case, crosstalk between organisms
affiliating with different species may take place.
The possible occurrence of interspecies communication is also inferred from the
distribution of genes involved in the cell-cell signaling as observed with regard to
those encoding AHL synthase and receptor. Usually, the AHL synthase and receptor
are encoded by sequences adjacent to each other. However, some bacteria retain only
25 Invisible Interactions between Microorganisms
533
density-dependent control of the bacterial community is termed quorum sensing.
Another group of autoregulatory molecules precisely characterized for their
actions are the gamma-butyrolactones (GBLs) produced by Streptomyces species
(Horinouchi et al. 2010). Despite being prokaryotes, Streptomyces and related
bacteria exhibit a complex life cycle resembling that of filamentous fungi. In the
vegetative growth phase, the organism extends the projecting “substrate mycelium”—those mycelia that maintain contact with the substrate being used to sustain
the fungus. Then, the substrate mycelium forms an aerial mycelium, which culminates in a spore chain. The cellular development from substrate to aerial mycelium is
genetically linked to the production of secondary metabolites, including those that
have antibiotic activity. In this life cycle, GBLs serve as a switch for the initiation of
secondary metabolism and cell differentiation during the change from producing
substrate to aerial mycelium. Probably, GBL-mediated signaling causes the cells
within a colony to synchronize and simultaneously initiate drastic cellular development. Without such harmonization, antibiotics produced by some cells may kill
others. In the case of streptomycin whose production is controlled by a GBL called
A-factor, the self-resistance gene located in the center of the biosynthetic gene
cluster is induced prior to the expression of the adjacent biosynthetic genes.
[I would guess the rest of a fungal colony intrinsically is resistant to its selfproduced antifungal agents unless resistance to its own antimicrobial compounds
must be induced].
In addition to lactones, structurally diverged small molecules, including those
with peptidic and furanosyl backbones, are known to direct social behavior
of specific groups of bacteria (Horinouchi et al. 2010). The original identification
of these cell-cell signaling molecules occurred in a study focusing on the expression
of a specific phenotype, such as antibiotic production and biofilm formation in a
given bacterial species, which is clearly observed in laboratory conditions. This, in
turn, suggests that similar communication to control microbial functions or phenotypes invisible to researchers using conventional manipulation techniques likely also
exists in other microbial groups but remains unknown.
25.2.2.4 Interspecies Communication
The above mentioned lactone signals retain structural divergence in terms of their
alkyl side chains. The strict ligand selectivity of its cognate receptor distinguishes
the true signal from other structurally similar derivatives, thus establishing speciesspecific communication. On the other hand, some strains or species share an autoinducer of identical chemical structure. In such a case, crosstalk between organisms
affiliating with different species may take place.
The possible occurrence of interspecies communication is also inferred from the
distribution of genes involved in the cell-cell signaling as observed with regard to
those encoding AHL synthase and receptor. Usually, the AHL synthase and receptor
are encoded by sequences adjacent to each other. However, some bacteria retain only
25 Invisible Interactions between Microorganisms
533