Mechanisms of Photoacclimation on Photosynthesis Level in Cyanobacteria

Abstract

Cyanobacteria are oxygenic photoautotrophic prokaryotes, which develop in many aquatic environments, both freshwater and marine. They successfully grow in response to increasing eutrophication of water, but also because of shifts in the equilibrium of ecosystems (Stal et al., 2003). Cyanobacteria possess many unique adaptations allowing optimal growth and persistence, and the ability to out-compete algae during favorable conditions. For instance, many species are buoyant due to the possession of gas vesicles, some of them are capable of fixing N2, and unlike algae, which require carbon dioxide gas for photosynthesis, most cyanobacteria can utilize other sources of carbon, like bicarbonate, which are more plentiful in alkaline or high pH environments. The cyanobacteria live in a dynamic environment and are exposed to diurnal fluctuations of light. Planktonic species experience differences in irradiance when mixed in the water column (Staal et al., 2002), whereas mat-forming cyanobacteria are exposed to changes in light intensity caused by sediment covering or sediment dispersion. Such rapidly changing environmental factors forced photoautotrophic organisms to develop many acclimation mechanisms to minimize stress due to low and high light intensities. High irradiance may damage photosynthetic apparatus by photooxidation of chlorophyll a molecules. Some carotenoid pigments may provide effective protection against such disadvantageous influence of light (Hirschberg & Chamovitz, 1994; Steiger et al., 1999; Lakatos et al., 2001; MacIntyre et al., 2002). Photosynthetic organisms respond to decreased light intensity by increasing the size or/and the number of photosynthetic units (PSU) whose changes, in turn, can be reflected in characteristic patterns of P-E curves (Platt et al., 1980; Prezelin, 1981; Ramus, 1981; Richardson et al., 1983; Henley, 1993; Dring, 1998; Mouget et al., 1999; MacIntyre et al., 2002; Jodlowska & Latala, 2010). Variation in α and Pm (expressed per biomass or per chlorophyll a unit) plays a key part in interpreting physiological responses to changes in environmental conditions. The aim of this review was to present exceptional properties of two different cyanobacteria, planktonic and benthic, their abilities to changing environmental condition, especially to irradiance. This information would be helpful in understanding the phenomenon of mass formation of cyanobacterial blooms worldwide, and would be very useful to interpret the domination of cyanobacteria in water ecosystem in summer months.