SUMMARY: Non-smooth mutants of strain 2 with known lipo-polysaccharide (LPS) defects were tested for sensitivity to smooth-specific phages (P22 and P22h and a newly isolated phage, 9NA, active on P22 lysogens); Felix O phage; and several rough-specific phages including C21. Smooth strains were sensitive only to the smooth-specific and Felix O phages. Six mutants (unable to make O chains) were sensitive to Felix O and all the rough-specific phages except C21 (pattern R-sens). Of nine mutants (presumed to have LPS core defects) four were R-sens, six were resistant to Felix O and some rough-specific phages (pattern R-res-1), and one was also resistant to phage Br2 (pattern R-res-2). The phage sensitivity of phosphomannoisomerase () mutants was the same as that of mutants, except that they were partly sensitive to P22h. UDPgalactose-epimerase-negative mutants were sensitive to C21 and various rough-specific phages in-cluding Br2 (pattern Epi-). An mutant (unable to polymerize O repeat units) was sensitive only to Felix O and P221 (pattern Zsr). A part-rough mutant of class D (with abnormally few O chains) was incompletely resistant to smooth-specific phages, resistant to Felix O but sensitive to all rough-specific phages except C21 (pattern D-).

Spontaneous and mutagen-induced non-smooth mutants were isolated from strains with appropriate markers by selection with Felix O and/or P22 phage. (One parent strain used was non-lysogenic for Fels 2, for which wild-type is lysogenic. Lysogeny for Fels 2 did not affect sensitivity to the other phages.) Some mutants gave new sensitivity patterns. Mutants of these and of previously unmapped classes were crossed with smooth Hfr strains. The loci of two mutants and loci of two others were located in the segment. Three mutants of pattern R-sens yielded O-specific hapten but mapped near ; they are believed to be unable to transfer O chains from antigen carrier lipid to the LPS core as a result of mutation at Six mutants of pattern R-sens were smooth in cultural and serological properties; they mapped near and are probably leaky mutants. Many mutants had the class D part-rough phenotype, divisible by phage sensitivities into patterns D-1, D-2 and D-3. Mutants of all three classes mapped near they are likely to be mutants, perhaps leaky, with LPS core defects which hinder but do not prevent attachment of O chains. Two classes were sensitive to C21 (Wilkinson&Stocker, 1968): mutants, of pattern Epi-, unable to add the main-chain galactose unit of the core; and mutants, resistant to Br2 (pattern Epi-2), unable to add the proximal glucose unit. Both loci mapped in or near the segment. Several non-smooth mutants did not grow in the presence of bile-salts. Three mutants () made LPS deficient of the distal heptose unit; one mutant () was unable to add the proximal heptose unit. Both these loci mapped in or near the segment.


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