Function of sll1906, a member of the bacteriochlorophyll delivery family, in the cyanobacterium synechocystis sp. PCC 6803

A deletion mutation was introduced into the sll1906 gene in the cyanobacterium Synechocystis sp. PCC 6803 to examine the function of Sll1906, a member of the putative “bacteriochlorophyll delivery” protein family. The Sll1906 sequence contains possible chlorophyll-binding sites. The pigment profile indicated that the chlorophyll and carotenoids contents were not altered in the mutant, and no chlorophyll precursors accumulated. According to the oxygen evolution and 77 K fluorescence emission spectra, the PSII activity and PSII/PSI ratio remained the same upon deletion of the gene. The sll1906 deletion was also introduced into the chlL⁻ background mutant strain, in which chlorophyll is synthesized in the light only. When grown in light-activated heterotrophic growth (LAHG) conditions, the rate of chlorophyll degradation in the chlL ⁻sll1906⁻mutant was similar to that in the chlL ⁻ background strain. When cells were returned to continuous illumination after a week of growth under LAHG conditions, both the rate of chlorophyll synthesis and chlorophyll-dependent photosystem biogenesis were monitored. The deletion of the sll1906 gene affected neither. Although the sll1906 deletion did not affect chlorophyll degradation/biosynthesis and photosystem assembly, Sll1906 could still be involved in these processes as other pathways may compensate for the absence of Sll1906.