Contributions of anoxygenic and oxygenic phototrophy and chemolithotrophy to carbon and oxygen fluxes in aquatic environments

Abstract

Estimates of aquatic primary productivity at local, regional or global scales commonly concentrate on oxygenic photolithotrophy. The analysis presented here briefly considers the occurrence and metabolism of other autotrophs sensu lato, i.e. not just the organisms with an autotrophic inorganic carbon assimilation machinery. These other autotrophs include chemolithotrophs and anoxygenic photolithotrophs, of which some use the photosynthetic carbon reduction cycle as do oxygenic photolithotrophs, while others use one of 4 other pathways. The category of other autotrophs also includes organisms that possess photochemical energy transduction machinery but lack autotrophic carbon assimilation; light stimulates the growth rates of these autotrophs and/or increases the fraction of the organic carbon substrate used that is converted into cell material when using light energy. Organisms lacking autotrophic inorganic carbon assimilation influence food webs by increasing the rate, or efficiency, of conversion of dissolved organic carbon ultimately derived from autotrophic inorganic carbon assimilation into particulate organic carbon. Chemolithotrophs and anoxygenic autotrophs today depend on the activities of oxygenic chemolithotrophs for one or more of their growth substrates, and thus contribute to global net primary productivity but not to global gross primary productivity. Global net aquatic primary productivity by oxygenic photolithotrophs is at least 50 Pg C yr . Before the occurrence of oxygenic photolithotrophs in the Archaean, chemolithotrophs and anoxygenic photolithotrophs had a net primary productivity of about 3.4 Pg C yr -1 , which is higher than the present values largely because anoxygenic photolithotrophs were able to inhabit the euphotic zone worldwide.KEY WORDS: Archaean · 3-hydroxypropionate pathway · Inorganic carbon concentrating mechanisms · Photosynthetic carbon reduction cycle · Reductive tricarboxylic acid cycle · Resource use · Ribulose bisphosphate carboxylase-oxygenase Resale or republication not permitted without written consent of the publisherContribution to AME Special 2 'Progress and perspectives in aquatic primary productivity'

Algal evolution in relation to atmospheric CO 2 : carboxylases, carbon-concentrating mechanisms and carbon oxidation cycles

“…For lack of accurate information, the resource cost of synthesizing the enzymic machinery needed to fix one mole of CO 2 per second from the present atmospheric CO 2 concentration is not shown in table 2. This value is a function of the stoichiometry of the enzymic protein components in the pathway, with that of the carboxylase(s) set by their CO 2 affinity, and the M r (relative molecular mass) values of the enzymes [40,41]. Here, the relatively lowspecific reaction rate and high M r of Rubisco would tend to make the Rubisco-PCRC pathway expensive at present CO 2 concentrations, even without the O 2 effect, though some other pathways are probably at least as expensive as a result of the low CO 2 affinity of their carboxylases and the consequent large quantity of carboxylase needed to fix one mole of CO 2 per second from the present atmospheric CO 2 concentration.…”

“…Six pathways of autotrophic CO 2 fixation are known in extant organisms, including ribulose bisphosphate carboxylase-oxygenase carboxylase activity in the photosynthetic carbon reduction cycle (Rubisco-PCRC), using CO 2 as the inorganic carbon species assimilated, which is at the core of inorganic carbon assimilation in extant oxygenic photosynthetic organisms [40][41][42][43][44][45]. These pathways are summarized in table 2 with respect to their stoichiometric requirement for reductant and ATP, their affinities for inorganic carbon expressed in terms of the half-saturation value for CO 2 and the influence of oxygen on their functioning.…”

A function-based screen for seeking RubisCO active clones from metagenomes: novel enzymes influencing RubisCO activity

“…Four types of structural RubisCOs are currently distinguished, of which two types, form I (CbbLS) and form II (CbbM), are known to operate in the classical autotrophic CB cycle (Tabita et al, 2007). RubisCO is present in all plants, cyanobacteria and many autotrophic bacteria (Berg, 2011) and is believed to be the most abundant protein on Earth (Ellis, 1979;Raven, 2009). Hence, the CB cycle and the RubisCO enzymes are of fundamental importance for global primary production and it is vital to better understand RubisCO evolution and its diversity.…”

Life in the lithosphere, kinetics and the prospects for life elsewhere

“…The primary net productivity of the present-day Biofilm has been calculated by a number of authors and is estimated to be approximately 1 × 10 16 mol C yr −1 [15,107] with a gross productivity around twice this [107]. The potential productivity of the Biofilm without photosynthesis, and when iron is derived by a direct interaction between life and the lithosphere (i.e.…”

“…Redox couples produced by volcanic and active geochemical and hydrological processes would have provided a diversity of energy sources on the pre-oxygenic photosynthetic Earth [31,[105][106][107].…”