Mechanisms of Acido-Tolerance and Characteristics of Photosystems in an Acidophilic and Thermophilic Red Alga, Cyanidium Caldarium

Abstract

In this chapter, we describe the mechanisms of acido-tolerance in an acido-and thermo-philic red alga, Cyanidium caldarium. In spite of the extremely acidic environments it inhabits, the intracellular pH of Cyanidium cells is kept neutral by pumping out the protons previously leaked into the cells according to the steep pH gradient. The H + pump is driven by the plasma membrane ATPase, utilizing intracellular ATP produced by both oxidative phosphorylation and cyclic photophosphorylation via photosystem I. We also describe the characteristics and function of the two photosystems, Photosystem I (PSI) and II (PSII) in Cyanidium caldarium in comparison with those of cyanobacteria, other eukaryotic algae and higher plants, based on the crystal structures of the two complexes reported so far.

The lowering of external pH in confined environments by thermo‐acidophilic algae (class: Cyanidiophyceae)

“…The lowering of pH was presumably by the previously described mechanism of rapid ATP‐dependent H + efflux (Kura‐Hotta and Enami, 1981; 1984; Enami and Kura‐Hotta, ; Enami et al ., ).…”

Phycobiliproteins from extreme environments and their potential applications

“…through several adaptations, including a plasma membrane with reduced permeability to protons, active ATP-dependent proton export, and/or coupled export, where a symporter or antiporter uses the driving force of a different ion to remove protons (Beardall and Entwisle, 1984;Messerli et al, 2005;Enami et al, 2010;Madigan et al 2018). Thus, PBPs from acidophiles are generally not exposed to acidic environments, such that PBPs extracted from acidophilic species show similar stability characteristics to mesophilic species under low pH conditions (Patel et al, 2004;Antelo et al, 2008;Chaiklahan et al, 2012;Patel et al, 2018).…”

A Reaction Center-dependent Photoprotection Mechanism in a Highly Robust Photosystem II from an Extremophilic Red Alga, Cyanidioschyzon merolae

“…merolae belongs to the rhodophytan order Cyanidiales, whose members thrive in acidic hot springs (18) and are unique among phototrophs in the ability to live at extremely low pH (pH 0.2-4) and moderately high temperatures (40 -56°C). Despite such an extremely acidic environment, the intracellular pH of these algae is most likely neutral due to the active H ϩ efflux across the plasma membrane (19). C. merolae is considered to be one of the most primitive eukaryotic phototrophs because it diverged near the root of the red algal lineage that forms a basal group within the photosynthetic eukaryotes (20).…”