Exploring Components of the CO 2 -Concentrating Mechanism in Alkaliphilic Cyanobacteria Through Genome-Based Analysis

Abstract

In cyanobacteria, the CO2-concentrating mechanism (CCM) is a vital biological process that provides effective photosynthetic CO2 fixation by elevating the CO2 level near the active site of Rubisco. This process enables the adaptation of cyanobacteria to various habitats, particularly in CO2-limited environments. Although CCM of freshwater and marine cyanobacteria are well studied, there is limited information on the CCM of cyanobacteria living under alkaline environments. Here, we aimed to explore the molecular components of CCM in 12 alkaliphilic cyanobacteria through genome-based analysis. These cyanobacteria included 6 moderate alkaliphiles; Pleurocapsa sp. PCC 7327, Synechococcus spp., Cyanobacterium spp., Spirulina subsalsa PCC 9445, and 6 strong alkaliphiles (i.e. Arthrospira spp.). The results showed that both groups belong to β-cyanobacteria based on β-carboxysome shell proteins with form 1B of Rubisco. They also contained standard genes, ccmKLMNO cluster, which is essential for β-carboxysome formation. Most strains did not have the high-affinity Na+/HCO3− symporter SbtA and the medium-affinity ATP-dependent HCO3− transporter BCT1. Specifically, all strong alkaliphiles appeared to lack BCT1. Beside the transport systems, carboxysomal β-CA, CcaA, was absent in all alkaliphiles, except for three moderate alkaliphiles: Pleurocapsa sp. PCC 7327, Cyanobacteriumstranieri PCC 7202, and Spirulina subsalsa PCC 9445. Furthermore, comparative analysis of the CCM components among freshwater, marine, and alkaliphilic β-cyanobacteria revealed that the basic molecular components of the CCM in the alkaliphilic cyanobacteria seemed to share more degrees of similarity with freshwater than marine cyanobacteria. These findings provide a relationship between the CCM components of cyanobacteria and their habitats.

Insights on the Functions and Ecophysiological Relevance of the Diverse Carbonic Anhydrases in Microalgae

“…around Rubisco embedded within a polyhedral compartment called a carboxysome, 1000 times above the external CO 2 concentration [39]. CCM components have been described both in marine and freshwater cyanobacteria and recently in cyanobacteria living in alkaline lakes [53]. Most bicarbonate transporters belong to the solute carrier family (SLC) and have been well described in mammals and humans [54]; however, other types of transporters have also been found in photosynthetic organisms.…”

“…It is encoded in the cmpABCD operon, which is highly induced by low CO 2 [56]. However, all strong alkaliphilic cyanobacteria lack this transporter [53]. Other transporters described in cyanobacteria include the two Na + -dependent HCO 3 − plasma membrane transporters SbtA (a sodium-dependent HCO 3 − symporter; with a K 0.5 for bicarbonate < 5 µM and low flux of HCO 3 − uptake), which was shown recently to be allosterically regulated [57], and BicA (a sulfate permease or SulP-type sodium-dependent HCO 3 -transporter) that has a low affinity for HCO 3 − (K 0.5 =70-150 µM) and a high flux of HCO 3 − uptake [55,58].…”

An Improved Genome-Scale Metabolic Model of Arthrospira platensis C1 (iAK888) and Its Application in Glycogen Overproduction

“…Subsequently, a list of GPR associations was assembled and manually curated to reflect actual physiology of A. platensis C1 based on various information sources including biochemical databases [25,29,30], literatures [31,32,33,34], and curated genome-scale models, Synechocystis sp. PCC6803 [35] and Escherichia coli [36].…”

Effect of CO2 Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans

“…The dominant source of available inorganic carbon (Ci) in circumneutral and slightly alkaline environments such as terrestrial fresh water and oceans is bicarbonate (HCO - 3 ) with lower concentrations of dissolved CO 2 (Mangan et al, 2016). The majority of models for prokaryotic Ci uptake and assimilation have been elucidated for organisms, such as cyanobacteria, that inhabit these environments (Burnap et al, 2015; Klanchui et al, 2017). Cyanobacteria fix carbon via the Calvin-Benson-Bassham (CBB) cycle and use a variety of carbon concentration mechanisms (CCMs) to take up CO 2 or bicarbonate and provide CO 2 to the carbon fixation enzyme, ribulose bisphosphate carboxylase-oxygenase (RubisCO).…”