Abstract
By sensing changes in one or few environmental factors biological systems can anticipate future changes in multiple factors over a wide range of time scales (daily to seasonal). This anticipatory behavior is important to the fitness of diverse species, and in context of the diurnal cycle it is overall typical of eukaryotes and some photoautotrophic bacteria but is yet to be observed in archaea. Here, we report the first observation of light-dark (LD)-entrained diurnal oscillatory transcription in up to 12% of all genes of a halophilic archaeon Halobacterium salinarum NRC-1. Significantly, the diurnally entrained transcription was observed under constant darkness after removal of the LD stimulus (free-running rhythms). The memory of diurnal entrainment was also associated with the synchronization of oxic and anoxic physiologies to the LD cycle. Our results suggest that under nutrient limited conditions halophilic archaea take advantage of the causal influence of sunlight (via temperature) on O2 diffusivity in a closed hypersaline environment to streamline their physiology and operate oxically during nighttime and anoxically during daytime.
Highlights
The ability to anticipate impending environmental change(s) and mount a preparative response is crucial to the fitness of all organisms [1,2]. Such preparatory behavior has been observed over a wide range of time scales and is mediated via sensing, internalizing and subsequently recalling fluctuation patterns in the specific environmental factor(s) (EFs). Such behavior can result from the ability of biological systems to internalize and use reproducible interrelationships among EFs such that by sensing a change in one or few EFs they are informed of impending changes in other EFs [3]
Taken together with substantial evidence for light-mediated global gene regulation in this organism [15,16,17], these observations make a compelling case for investigating the feasibility of entraining global expression changes in Halobacterium salinarum NRC-1 by prolonged culturing under diurnal 12h:12h light:dark (LD) cycles
We have previously demonstrated that a significant number of genes in H. salinarum NRC-1 are differentially regulated as a direct consequence of changes in O2 availability [18]
Summary
The ability to anticipate impending environmental change(s) and mount a preparative response is crucial to the fitness of all organisms [1,2]. Taken together with substantial evidence for light-mediated global gene regulation in this organism [15,16,17], these observations make a compelling case for investigating the feasibility of entraining global expression changes in Halobacterium salinarum NRC-1 by prolonged culturing under diurnal 12h:12h light:dark (LD) cycles.
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