Investigation of unusual growth and phenotypic characteristics of plasmid-containing and plasmid-free strains of oligotrophic bacterium Ancylobacter vacuolatus.

The oligotrophic bacterium Ancylobacter vacuolatus contains two large plasmids pREV1 and pREV2 (about 150 and 250 kb, respectively). Plasmid pREV1 carries the genes responsible for resistance to chloramphenicol, trimethoprim and y-irradiation. Plasmid pREV2 carries the genes responsible for resistance to beta-lactam antibiotics and formation of gas vacuoles. The ability to grow under oligotrophic conditions did not depend directly on either plasmid and was probably chromosome-encoded. Nevertheless, strains lacking the pREV2 plasmid had an improved capacity for growth in enriched media, as is evident from the following findings: 1) the growth rate of the strains lacking pREV2 was about 60% higher with an induction time of about two times less than those for strains carrying the plasmid; 2) the overall cell yield in rich media and colony size on non-oligotrophic agarized media increased with removal of pREV2; 3) the characteristic change in cell morphology occurring in the wild type ofA. vacuolatus when switched from oligotrophic to eutrophic growth conditions was not observed in the strains lacking pREV2; 4) bacterial strains lacking pREV2 exhibited significantly higher rRNA content than the parent strain. As a possible explanation for these phenomena, we suggest that the pREV2 plasmid carries gene(s) for protein(s) acting as repressor(s) of expression of some enzymes involved in eutrophic metabolism. Such protein(s) probably participate in switching between the oligotrophic and eutrophic types of metabolism in response to changing nutrient supply in the environment.

[Some aspects of antibiotic resistance of oligotrophic bacteria]. / Nekotorye aspekty antibiotikorezistentnosti oligotrofnykh bakterii.

Antibiotic resistance spectra of a large group of oligotrophic and eutrophic bacteria from the open soil and aquatic ecosystems were studied. It was shown that sometimes antibiotic resistance of the oligotrophs was of plasmid nature. A possible transfer of plasmid antibiotic resistance from oligotrophs to pathogenic eutrophic soil and aquatic bacteria in the natural ecosystems is discussed. It was demonstrated that there was no insurmountable transcription/translation barriers between oligotrophic and eutrophic bacteria though the two bacterial groups are taxonomically and evolutionally very distant. A hypothesis was proposed that oligotrophic bacteria are likely to be one of the possible pools of plasmid antibiotic resistance for pathogenic microbes. Plasmid-free strains of some oligotrophic bacteria were selected. With the method of antibioticograms, taxonomic patterns for oligotrophic bacteria of the central group were developed.

[Free iron in bacteria]. / Svobodnoe zhelezo v bakteriiakh.

Free iron content has been estimated in autotrophic and heterotrophic bacteria. It constituted 40-50 micrograms/g dry weight as compared to 15 micrograms/g dry weight in animal cells. A method for estimation of free iron has been proposed. It is based on formation of paramagnetic dinitrosyl iron complexes by free iron and protein thiol groups or low molecular weight thiol ligands. The reasons for high iron content in bacteria have been discussed.

Evolutionary relationship of some stalked and budding bacteria (genera Caulobacter, "Hyphobacter", Hyphomonas and Hyphomicrobium) as studied by the new integral taxonomical method.

A new approach was developed for the determination of taxonomic and evolutional relationships among four genera of oligotrophic bacteria. The main idea of this approach is the algorithmized integrative analysis of the morphological and physiological specificity of these bacteria, their 5S rRNA sequences, fatty acid and lipid composition of their membranes, as well as their sensitivity to a large variety of antibiotics. It was shown that the genera Caulobacter and Hyphomonas are closely related to each other, but they are both distant from Hyphomicrobium species. The new genus, "Hyphobacter", is placed between Caulobacter and Hyphomonas. Taxonomic heterogeneity was found to exist within the genera Caulobacter and Hyphomicrobium. Evolutional pathways from Caulobacter to Hyphomicrobium are proposed on the basis of the present data. No correlations were found between the cell morphology of the organisms and their geno- and chemotaxonomy.

[Clustering of oligotrophic microorganisms on the basis of their antibiotic resistance and dynamic membrane characteristics]. / Klasterizatsiia oligotrofnykh mikroorganizmov na osnovanii ustoichivosti k antibiotikam i dinamicheskikh kharakteristik membran.

Some oligotrophic microorganisms were characterised in terms of their resistance against a broad spectrum of antibiotics and certain dynamic parameters of membranes obtained by analysing the EPR and NMR spectra. The oligotrophic bacteria differed in these characteristics from eutrophic microorganisms. The oligotrophic bacteria were subdivided into 3-4 subgroups different in many of the studied parameters. A new chemotaxonomic approach was proposed for the oligotrophic bacteria basing on the analysis of antibioticograms.

Drug-dependent mutants in yeast Saccharomyces cerevisiae.

Mutations in sup1 and sup2 genes may cause cycloheximide-dependent growth in yeast Saccharomyces cerevisiae. Two classes of such mutants are described in the paper: 1) high temperature sensitive mutants, which do not express their sensitivity to nonpermissive temperature in the presence of cycloheximide (conditionally dependent) and 2) mutants unable to grow in the absence of the drug (true dependent). Some of the mutants of both classes express dependence toward another antibiotic - trichodermine. The binding of H(3)-labelled cycloheximide studied by equilibrium dialysis has demonstrated that both 80S ribosomes and 60S subunits isolated from conditionally dependent mutant showed a higher affinity for the drug compared to that of a parent strain. The number of binding sites per ribosome or per 60S subunit in the cycloheximide dependent mutant remains unchanged.Circular dichroism spectra of a mutant ribosomes in the presence as well as in the absence of antibiotic revealed that sup1 and sup2 mutations alter conformation of the yeast cytoplasmic ribosomes. The binding of cycloheximide to mutant ribosomes induces a conformational shift, which presumably compensates for their functional defect.

Ribosomal protein S1 associates with Escherichia coli ribosomal 30-S subunit by means of protein-protein interactions.

Ribosomal proteins S1 when associated with the 30-S subunit does not interact with 16-S RNA but its binding is determined mostly by protein-protein interactions. These conclusions are based on the following data. 1. Ultraviolet irradiation (lambda = 254 nm) of the 30-S subunit does not result in the covalent cross-linking of S1 with 16-S RNA at irradiation doses up to 150 quanta/nucleotide, whereas the irradiation under the same conditions of S1 . polynucleotide complexes [S1 . poly(U), S1 . poly(A) and S1 . Q beta phage RNA] induces effective formation of polynucleotide-protein cross-links. 2. Mild treatment of 30-S subunits lacking S-1 with RNase A or with cobra venom endonuclease results in removal of 10--20% of the total nucleotide material but does not affect their sedimentation characteristics of their S1 binding capacity. 3. The association of S1 with S1-depleted 30-S subunits is insensitive to aurintricarboxylic acid, which is known as a strong inhibitor of complex formation between S1 and polynucleotides. 4. Mild trypsin treatment of S1-depleted 30-S subunits greatly reduces their S1 binding capacity.