Abstract
Heme oxygenase (HO) catalyzes the oxygen-dependent cleavage of porphyrin ring of heme, producing biliverdin IXα in phycobilin biosynthesis. In the genome of the cyanobacterium Synechocystis sp. PCC 6803 there are two genes, ho1 (sll1184) and ho2 (sll1875), encoding heme oxygenase isoforms. We have isolated two mutants, Δho1 and Δho2, in which ho1 and ho2 were inactivated, respectively. The Δho1 mutant failed to grow under aerobic conditions and grew significantly slower than wild type under anaerobic (micro-oxic) conditions. The Δho2 mutant grew as well as wild type under both conditions. This result suggested that ho1 is essential for growth under aerobic conditions and is dispensable under micro-oxic conditions and that HO1 operates together with HO2 induced by oxygen-limited conditions. To understand the physiological significance of HO2, we are examining whether overexpression of ho2 restores the growth defect of Δho1. We will also present pigment analysis of these mutants.
