Phenotypic plasticity and the changing environment

Abstract

Cyanobacteria probably exhibit the widest range of diversity in growth habitats of all photosynthetic organisms.They are found in cold and hot, alkaline and acid, marine, freshwater, saline, terrestrial and symbiotic environments.In addition to this, they originated on earth at least 2.5 billion years ago and have evolved through periods of dramatic O 2 increases, CO 2 declines and temperature changes.One of the key problems they have faced through evolution and in their current environments is the capture of CO 2 and its efficient use by Rubisco in photosynthesis.A central response to this challenge has been the development of a CO 2 concentrating mechanism (CCM) that can be adapted to various environmental limitations.The functional elements of this CCM are: (i) the containment of Rubisco in carboxysome protein microbodies within the cell (the sites of CO 2 elevation), and (ii) the presence of several inorganic carbon (Ci) transporters that deliver HCO 3 ÿ intracellularly.Cyanobacteria show both species adaptation and acclimation of this mechanism.Between species, there are differences in the suites of Ci transporters in each genome, the nature of the carboxysome structures and the functional roles of carbonic anhydrases.Within a species, different CCM activities can be induced depending on the Ci availability in the environment.This acclimation is largely based on the induction of multiple Ci transporters with different affinities and specificities for either CO 2 or HCO 3 ÿ as substrates.These features will be discussed in relation to our current knowledge of the genomes of diverse cyanobacteria and their ecological environments.