Minimal requirements in defined media for improved growth of some radio-resistant pink tetracocci.

Defined media permitting extensive growth of representative pink radio-resistant tetracocci (Micrococcus radiodurans, Micrococcus roseus, and Micrococcus radiophilus) and two controls (an ultraviolet-sensitive mutant of M. radiodurans and Micrococcus luteus) are described. Availability of Fe (especially Fe3+) proved essential for good growth, as evidenced by (i) favorable effects of hydroxamic acids, e.g., salicylhydroxamic acid, and (ii) the growth promotion by hemin when joined with elevated concentrations of Fe. Cobalamin (B12) and methionine were interchangeable as an absolute requirement for methionine not affected by B12. M. luteus required neither. Pink radio-resistant micrococci may form a coherent group. Some divergences among them might be attributable to the method for isolating them, which for ordinary bacteria would be mutagenic to the point of total lethality. The ecology of these tetracocci vis-à-vis other pink-red radio-resistant organisms is discussed in relation to a question: can these bacteria be isolated without dependence on radiation as the cardinal selective factor?