[Electron microscopic study of the developmental cycle of an actinomycete endosymbiont in the nitrogen-fixing nodules on the roots of Alnus glutinosa]. / Elektronno-mikroskopicheskoe izuchenie tsikla razvitiia aktinomitseta éndosimbionta v azotfiksiruiushchikh kluben'kakh na korniakh Alnus glutinosa.

As has been shown by electron microscopy, the development of the endosymbiont in the nitrogen-fixing nodules of A. glutinosa proceeds either along the known (hyphae leads to vesicles) or less convenient pattern (hyphae leads to sporangia leads to spores). The paper presents more complete information about the structure of layers which separate the endosymbiont from the cytoplasm of host cells and about changes in the structure of the both partners accompanying sporogenesis.

[Survival of Rhizobium meliloti in soil studied by genetic labeling]. / Izuchenie vyzhivaemosti Rhizobium leliloti v pochve metodom geneticheskoi markirovki

The number of cells of a mutant of Rhizobium meliloti resistant to streptomycin decreased to 10(6) per 1 g of soil during 3-5 days and remained at this level for at least a month when 10(8) cells of the mutant per 1 g were introduced into non-sterile soil. Factors causing such a stability of the population are discussed.

[Factors of multiple resistance to antibiotics in nodule bacteria]. / Faktory mnozhestvennoi ustoichivosti k antibiotikam u kluben'kovykh bakterii

Multiple resistance to antibiotics (penicillin, levomycetin, neomycin, tetracycline) was found in 15% of collection strains of nodule bacteria and in strains isolated from natural environment.

[The presence of Agrobacterium tumefaciens in lucerne root nodules]. / O nakhozhdenii Agrobacterium tumefaciens v kluben'kakh na korniakh liutserny

Agrobacterium tumefaciens does not penetrate into nodules on the roots of lucerne with the active strain of nodule bacterium as was established with the aid of genetic markers and plant selection. A nodule, whose shape was not typical and which did not fix nitrogen, was formed on the root of lucerne inoculated with the culture of Agrobacterium tumefaciens treated with UV. A bacterial strain isolated from the nodule was identical to A. tumefaciens according to its resistance to streptomycin and several cultural properties. Upon repeated inoculation with the isolated strain, nodules were formed in 50% cases.

[Selection methods of nodule bacteria]. / O metodakh selektsii kluben'kovykh bakterii

The aim of selecting nodule bacteria is to obtain stable and genetically pure strains with elevated effectiveness in the conditions of symbiosis with bean plants, sufficient viability and competing ability, which would survive in soil for a long time. The following methods have been suggested to solve this task: selection by plants using mutagenic factors; genetic markers; production of genetically homogeneous material; determination of the degree of persistance effectiveness in mutants.