SUMMARY: Sixty-three wild strains of were investigated. All 55 strains comprising groups 1 and 1 were found to be cryptic with regard to sucrose fermentation; they possessed competent enzyme systems but did not normally ferment the sugar. No enzyme capable of cleaving this sugar was extracted from the 3 strains of group 2 and the 5 strains belonging to group 3. Partially purified enzyme preparations from two strains of is and two cryptic strains were investigated; all four were constitutive β-D-fructofuranosidases capable of splitting raffinose to melibiose and fructose. Sucrose uptake studies showed that strains of groups 1, 1 and 2 did not accumulate sucrose from 1% (w/v) solution; the strains of group 3 accumulated large amounts of sucrose. None of the strains was permeable to maltose. The permeability barrier for sucrose was overcome by increasing its concentration to 5% (w/v). Under these conditions groups l and 1 strains fermented sucrose in peptone water within 36 hr. Sodium deoxycholate also changed the permeability barrier of some of the cryptic strains, enabling them to ferment 1% (w/v) sucrose promptly. After 3–11 days in 1% (w/v) sucrose peptone water all 55 cryptic , as well as the strains of group 3 fermented sucrose.

This fermentation was not caused by wild-type organisms, but resulted from the selection of sucrose-positive mutants which arose from the former and were capable of prompt sucrose fermentation. The mutants of strains of group 3 arose at lower rates than those from the cryptic strains. It is concluded that selective permeability to sucrose and β-D-fructofuranosidase activity are genetically distinct properties of Proteus. A scheme for the classification of phenotypes of is presented.


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