Analysis of Bacteriochlorophylls in Zinc-Containing Bacteriochlorophyll Producing Acidophilic Bacterium, Acidiphilium Rubrum, by High-Performance Liquid Chromatography
All known photosynthetic organisms possess magnesium-containing tetrapyrroles, namely chlorophylls and bacteriochlorophylls (Bchls), for light harvest and energy-generating charge separation. Very recently, one exception was found in the purple bacterium, Acidiphilium rubrum, which possesses zinc-containing Bchl a (Zn-Bchl a) as its major photosynthetic pigments . This finding modifies our common understanding that the naturally occurring chlorophylls and BchIs ubiquitously have a chelated magnesium atom at the center of macrocyclic ring. Zinc porphyrin derivatives are usually more stable than Mg-derivatives, and have been widely used in the studies of artificial photosynthesis . All known species of the genus Acidiphilium are chemoheterotrophic aerobes and extreme acidophilic bacteria showing optimum pH for growth at around 3.0, and belong to the α-subclass of Proteobacteria that includes many of typical Bchl-utilizing photosynthetic bacteria . Therefore, it is most likely that Acidiphilium species utilize Zn-Bchl instead of acid-labile Bchl in order to adapt their acidic environment, rather than they are evolutional ancestor of magnesium-containing Bchl-utilizing photosynthesis. Thus, an elucidation of Zn-Bchl a biosynthetic pathway in Acidiphilium species may provide insights as to how these bacteria adapt their photosynthesis by modulating a central metal of tetrapyrrole ring.
Key wordAcidiphilium Bchl Chi biosynthesis HPLC pH-dependence Zn-Bchl
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