“…In later investigations, A. Fjeld and S. Børresen, however, noticed that the high mutability is not a general trait of U. mutabilis but must have resided in only one of the three original isolates collected at Olhão Børresen 1975, Børresen andFjeld 1977). While this presumably genetically instable original strain unfortunately became lost in culture, the "mutabilis trait" still survived in certain of the mutants originated by this mechanism and in their spontaneous revertants Børresen 1975, Børresen andFjeld 1977). A number of these original spontaneous developmental mutants, such as "slender" (sl), "long" (l) (Føyn 1959), "bubble" (bu) (Fjeld 1970), "lumpy" (lu) (Bryhni 1974), "slen-deroid 1" (sd1), and "slenderiod 2" (sd2) (Fjeld and Børresen 1975), are still in culture, as well as the genetically stable form of the wildtype (Fjeld 1972).…”