Abstract
Second messengers are intracellular substances regulated by specific external stimuli globally known as first messengers. Cells rely on second messengers to generate rapid responses to environmental changes and the importance of their roles is becoming increasingly realized in cellular signaling research. Cyanobacteria are photooxygenic bacteria that inhabit most of Earth’s environments. The ability of cyanobacteria to survive in ecologically diverse habitats is due to their capacity to adapt and respond to environmental changes. This article reviews known second messenger-controlled physiological processes in cyanobacteria. Second messengers used in these systems include the element calcium (Ca2+), nucleotide-based guanosine tetraphosphate or pentaphosphate (ppGpp or pppGpp, represented as (p)ppGpp), cyclic adenosine 3’,5’-monophosphate (cAMP), cyclic dimeric GMP (c-di-GMP), cyclic guanosine 3’,5’-monophosphate (cGMP), and cyclic dimeric AMP (c-di-AMP), and the gaseous nitric oxide (NO). The discussion focuses on processes central to cyanobacteria, such as nitrogen fixation, light perception, photosynthesis-related processes, and gliding motility. In addition, we address future research trajectories needed to better understand the signaling networks and cross talk in the signaling pathways of these molecules in cyanobacteria. Second messengers have significant potential to be adapted as technological tools and we highlight possible novel and practical applications based on our understanding of these molecules and the signaling networks that they control.
Highlights
Microorganisms need to cope with variations in the external environment and rely on signaling molecules to translate these changes into intracellular responses to mediate adaptation to the new condition
Many cyanobacterial proteins contain light-responsive domains linked to domains that can impact c-di-GMP synthesis or degradation, suggesting that light is an important signal for altering c-di-GMP homeostasis and associated development, physiology and metabolism in cyanobacteria [16]
Proteins containing cAMP and cGMP synthesizing domains associated with photoreceptors have been engineered for potential optogenetic applications [111,112,113,114,115]; yet, as cAMP and cGMP are present in mammals these two second messengers may not be optimal for cell-based therapeutics
Summary
Microorganisms need to cope with variations in the external environment and rely on signaling molecules to translate these changes into intracellular responses to mediate adaptation to the new condition. Cyclic dimeric AMP (c-di-AMP) remains to be characterized in cyanobacteria All of these second messengers are commonly studied in pathogenic bacteria. Cyanobacteria exhibit extraordinary diversity in terms of genome plasticity, morphological characteristics, ecological niches, and physiological properties [11,12,13] These organisms generally rely on complex signal transduction systems, which reflect their diverse ecophysiological origins and abilities to colonize a wide range of habitats. Motility, and biofilm production are just some examples of physiological processes under the control of second messengers Regulatable control of these processes could lead to improvements in the efficiency of growing photosynthetic bacteria in partially or fully enclosed photobioreactors or other production platforms.
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