Inorganic Carbon Acquisition by Marine Autotrophs

Abstract

This chapter discusses inorganic carbon (C) acquisition by marine autotrophs. This chapter discusses the characteristics of inorganic C acquisition process responsible for major biogeochemical process. The chapter discusses the transport of inorganic C species from seawater to the site of carboxylation; the interconversions of inorganic C species that occur en route ; and the mechanism of the carboxylations, which occur in parallel to yielding carboxylic acids usable in biosynthesis leading to the production of all organic C in the organism, including any “photorespiratory” decarboxylation processes. There is great genetic and ecological diversity among marine autotrophs; even when chemolithotrophs and non-O 2 -evolving phototrophs are not considered, there is much more genetic diversity among marine photolithotrophic O 2 -evolvers than among terrestrial O 2 -evolvers. O 2 -evolvers bring about more than 90% of gross inorganic C assimilation in the oceans, and essentially all of this inorganic C is routed through Ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO), although in some instances some or all of this inorganic C has been subject to a prior carboxylation–decarboxylation cycle using enzymes other than RUBISCO. There have been variable results from attempts to demonstrate a higher inorganic C concentration inside the cells of marine O 2 -evolvers than in normal seawater for organisms, while gas-exchange characteristics suggest the occurrence of a CO 2 -concentrating mechanism. The evolution of inorganic C-assimilation systems in marine autotrophs will only be better understood when more is known of the present day mechanisms of inorganic C transport at the molecular genetic level.