Section 3 — Molecular and Microbial Genetics 



frequency of the transduced cells in the minimal 

 medium is due to the recovery of the cell from 

 the transducing element when it is in the non- 

 integrated form. 



Further experiments have shown that the 

 reduced frequency of transduction can be achiev- 

 ed not only by transferring the cells from com- 

 plete to minimal medium, but also by chilling the 

 cells in complete medium from 37 C to 0°C. 

 When the cells were treated in such a way, 10~ N 20 

 per cent of the amino acid pool was lost while 

 some amino acids were removed quantitatively. 

 Biochemical analysis of this fact leads to eluci- 

 dation of the importance of amino acid pool in 

 the genetic expression of a new marker. 



3.43. The Biochemistry of Dissociation of Bacillus 

 brevis GB. V. N. Stoletov, S. V. Shestacov, 

 V. M. Glazer, V. D. Filippov (Moscow, 

 U.S.S.R.). 



The comparative biochemical examination of 

 the dissociating forms of Bacillus brevis GB has 

 been carried out. The chemical constitution of 

 cells, the content of some significant metabolites, 

 some enzymic activities, and the occurrence of 

 some metabolic processes have been investigated 

 in rough R-form, smooth S-form, and in two 

 variants of mat flat M-form of B. brevis. R-form 

 and variants of M-form are known to synthesize 

 the gramicidin C in contrast with S-form and 

 second M-form variant. 



All studied variations of B. brevis have the 

 same nucleotide composition and DNA content. 

 Gramicidin-producing variants have been shown 

 to content the higher amounts of RNA. Flat 

 forms differ from R- and S-forms in their free 

 amino-acid and polypeptide content and compo- 

 sition, and the content of free nucleotides and 

 some phosphorus-containing fractions. 



The role of cell membrane in metabolic changes 

 in the time of dissociating transition are dis- 

 cussed with respect to the study of respiratory 

 characteristics of intact cells and protoplasts of 

 various dissociating forms of B. brevis. Specific 

 differences in lipide and polysacharide compo- 

 sition have been found for three forms of disso- 

 ciation. 



The activity of some amino-acid metabolism 

 enzymes of dissociating forms has been investi- 

 gated in respect to their capability to enzymic 

 induction, repression, and feed-back inhibition. 



Obtained results are interpreted as being due 

 to existence of correlation between certain 

 biochemical and cultural features in various 

 forms of B. brevis. The data of biochemical ana- 

 lysis of dissociants are regarded from the point 



of view of detection of regularity in metabolic 

 changes in the time of bacterial dissociation. The 

 latter is assumed to be a form of displaying the 

 special adaptive variability of microorganisms. 



3.44. Genetic Analysis of Streptomycin Dependence 

 in Proteus mirabilis. Helmut Bohme (Gaters- 

 leben, Kreis Aschersleben, Germany). 



By selection in the presence of streptomycin 

 several different streptomycin dependent (str-d) 

 mutants can be obtained from the same wild type 

 strain of P. mirabilis. Most of these str-d mutants 

 require for growth in minimal medium besides 

 streptomycin the aminoacids methionine, cys- 

 teine and arginine. All str-d mutants can be 

 transduced to nondependence by phages grown 

 in wild type (str-s) cells. Transduction with pha- 

 ges propagated in str-r mutants results exclusively 

 in str-r transductants; str-s, str-r and str-d thus 

 being allelic. Since in transductional crosses 

 between nine different str-d mutants no wild type 

 recombinants were obtained, the str-d mutations 

 seem to be multi-site mutations. By selection on 

 streptomycin-free nutrient agar streptomycin 

 nondependent revertants can be obtained from 

 str-d mutants. In most of the str-d strains two 

 types of revertants result: auxotrophic and proto- 

 trophic revertants. The numerical relation be- 

 tween these two types as well as the growth 

 factor (isoleucine and valine, in other cases 

 arginine) required by the auxotrophic revertants, 

 are specific for each str-d mutant. The auxotro- 

 phic revertants arise as result of a mutation in a 

 suppressor locus; it can be shown by transduction 

 with phages grown in these revertants that they 

 still contain the str-d allele. The suppressor could 

 not be transferred by transduction into str-d 

 strains. The auxotrophic revertants can be trans- 

 duced to prototrophy using phages grown in 

 wildtype bacteria. The resulting prototrophic 

 transductants further contain the suppressed 

 str-d allele. Thus in spite of the always simulta- 

 neous origin of the suppressor and the growth 

 factor requirement, both can be separated by 

 transduction. 



3.45. A Genetic Basis for Changing Virulence in Two 

 Plant Pathogenic Fungi. E. W. Buxton (Har- 

 penden. Great Britain). 



Mutants of physiologic races of Fusarium 

 oxysporum and Verticillium albo-atrum resistant 

 to acriflavine or actidione were used to show 

 how heterokaryosis and asexual recombination 



33 



