Dictyostelium discoideum, a soil-dwelling eukaryotic microorganism, encodes a manganese superoxide dismutase named SodM (formerly called SodE). Fluorescence of SodM-GFP fusion protein was detected in mitochondria of D. discoideum, indicating that SodM is a mitochondrialocalizing superoxide dismutase. Expression of sodM was observed throughout the life cycle. Maximum level of gene expression was observed at the aggregation stage. An sodM-overexpressing D. discoideum, sodMoe, grew faster and reached higher cell density in a liquid medium than did the wild type. Multicellular structures formed by sodMoe on a non-nutrient agar were larger in size than those formed by the wild type. These results indicate that SodM plays important roles both in growth and development of D. discoideum.
Dictyostelium discoideum amoebae grow as unicellular microorganisms until nutrients are depleted, while they aggregate and form multicellular structures under a starved condition. We established D. discoideum expressing a green fluorescent protein (GFP) under control of an upstream sequence of the gene for RecA, a mitochondria-localizing DNA repair enzyme. Multi-cellular structures formed by the strain were irradiated by 50 J/m2 UV light (254 nm) and GFP expression was analyzed. Fluorescence of GFP was observed not in the prestalk cells but in the prespore cells in the multicellular structures. The prestalk cells are programmed to die, while the prespore cells differentiate into viable spores. D. discoideum is thought to repair DNA damage in the prespore cells and maintain genomic integrity using a limited energy source.