Molecular responses to environmental stress

yanobacteria are remarkable for their ability to flourish in environments with widely fluctuating chemical and physical parameters, such as nutrient availability, light quality and intensity, temperature and osmotic conditions. This chapter focuses on the responses of cyanobacteria to changes in light intensity, light quality and macronutrient availability. Suboptimal light and nutrient conditions result in a number of specific and general responses that strongly influence the physiology of the cell. Some of the changes can be striking, while others are subtle; they can occur in minutes or take place over several days. In recent years knowledge of the molecular responses of cyanobacteria to stress conditions has increased considerably. Capacity to acclimate to suboptimal light levels for photosynthetic carbon fixation is unique among the bacteria. In contrast, an understanding of acclimation to nutrient deprivation has gained much from the information available from analyses of enteric bacteria, although cyanobacteria have a number of interesting deviations in their responses. Perhaps most provocative in studies of acclimation processes in cyanobacteria is the overlap among the responses elicited by different environmental stimuli, which suggests the existence of a hierarchy of responses and the involvement of global regulatory circuits.