Isolation ofMicrococcus radioduransOccurring in Radurized Sawdust Culture Media of Mushroom

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Abstract
Radio-resistant red pigmented micrococci were propagated from radurized sawdust culture media of mushroom subjected to from 1.0 to 2.0 Mrad and stored for one month at 20°C. Three strains, H 48, H 54 and H 55, were isolated from different samples of sawdust media. Many of the characteristics of strains H 54 and H 55 were the same as those of Micrococcus radiodurans R1 isolated by Anderson et al. On the contrary, strain H 48 had some distinct characteristics such as small cell size, nitrate-reducing property, requirement of riboflavin with thiamine for growth and salt-torelance. The GC content of the DNA of these strains ranged from 65 to 67 moles %, and their cell wall peptidglycan contained ornithine type subunit to warrant their description as the species of Micrococcus radiodurans. The resistances to gamma-radiation of these isolates were the same as that of strain R1. However, the shape of survival curves differed among the strains. The curves of H 54 and H 55 were sigmoidal like that of strain R1, but that of H 48 was roughly exponential. The D10 values of these strains incubated at 30°C for 40 hr ranged from 190 to 300 krad in 0.067m phosphate buffer.