nutritional deprivations (Baharoglu and Mazel 2014). The expression of a defensive
mechanism is linked to the sensing of the corresponding stress factor by a specific
signal transduction cascade. Bacterial genetic studies have progressed our understanding regarding how bacteria sense a stress signal and induce a specific function
that makes adaptation of the cells to the stress condition possible.
The major mode of an adaptive response occurs at the level of transcription.
Various kinds of transcriptional regulators and cognate sensors have been identified
and studied for the purpose of understanding their underlying signal transduction
pathways. Typically, two-component regulatory systems include a signaling module
that transmits the environmental signal to their specific gene expression regulation
partner (Groisman 2016). An example would be stress-response sigma factors which
specify the transcription of genes regulated by stress-response promoters and direct
the expression of stress-responsive genes. The adaptive response also occurs at
translational levels. This is mediated partially by the function of a specific RNA
structure called a riboswitch, whose change in conformation affects the efficiency in
translation of the genetic information encoded downstream from the switch.
25.2.1.3 Homeostatic Control
Adaptive responses contribute to cellular homeostasis. The sensing of damage and
starvation induces the expression of repair and nutritional uptake systems to restore a
healthy cellular structure and physiological state, respectively. Inner cellular homeostatic control involves second messengers, such as cyclic adenosine monophosphate
(cAMP), which is formed due to the cyclization of AMP by adenylate cyclase (Green
et al. 2014). The cAMP level serves as an indicator of the cellular metabolic state.
Feedback mechanisms induced by a change in the cAMP level function until the
cAMP level returns back to normal, hence restoring the original metabolic state and
maintaining it.
25.2.2 Secondary Structure: Cellular Interaction
The ability of inducing stress responses and subsequent self-restoration is critical to
the persistence of each organism. Hence, these mechanisms support the rigid
structure of an ecosystem at its most basic level. However, these are essentially the
conservative maintenance mechanisms within each organism that have no positive
effect on the structuring of the life community. Thus, other mechanisms should also
exist in the background of the structuring of rigid ecosystems. In this context, we can
reasonably speculate that intercellular associations play an important role. However,
knowledge on these associations has not been appropriately collected and analyzed,
especially regarding interactions between invisible microbial cells.
530
K. Ueda
mechanism is linked to the sensing of the corresponding stress factor by a specific
signal transduction cascade. Bacterial genetic studies have progressed our understanding regarding how bacteria sense a stress signal and induce a specific function
that makes adaptation of the cells to the stress condition possible.
The major mode of an adaptive response occurs at the level of transcription.
Various kinds of transcriptional regulators and cognate sensors have been identified
and studied for the purpose of understanding their underlying signal transduction
pathways. Typically, two-component regulatory systems include a signaling module
that transmits the environmental signal to their specific gene expression regulation
partner (Groisman 2016). An example would be stress-response sigma factors which
specify the transcription of genes regulated by stress-response promoters and direct
the expression of stress-responsive genes. The adaptive response also occurs at
translational levels. This is mediated partially by the function of a specific RNA
structure called a riboswitch, whose change in conformation affects the efficiency in
translation of the genetic information encoded downstream from the switch.
25.2.1.3 Homeostatic Control
Adaptive responses contribute to cellular homeostasis. The sensing of damage and
starvation induces the expression of repair and nutritional uptake systems to restore a
healthy cellular structure and physiological state, respectively. Inner cellular homeostatic control involves second messengers, such as cyclic adenosine monophosphate
(cAMP), which is formed due to the cyclization of AMP by adenylate cyclase (Green
et al. 2014). The cAMP level serves as an indicator of the cellular metabolic state.
Feedback mechanisms induced by a change in the cAMP level function until the
cAMP level returns back to normal, hence restoring the original metabolic state and
maintaining it.
25.2.2 Secondary Structure: Cellular Interaction
The ability of inducing stress responses and subsequent self-restoration is critical to
the persistence of each organism. Hence, these mechanisms support the rigid
structure of an ecosystem at its most basic level. However, these are essentially the
conservative maintenance mechanisms within each organism that have no positive
effect on the structuring of the life community. Thus, other mechanisms should also
exist in the background of the structuring of rigid ecosystems. In this context, we can
reasonably speculate that intercellular associations play an important role. However,
knowledge on these associations has not been appropriately collected and analyzed,
especially regarding interactions between invisible microbial cells.
530
K. Ueda