[Corrosive activity of natural microbial associations at various conditions of cultivation].

Influence of microbial associations isolated from different ecological niches on corrosion of mild steel was changed depending on composition of medium and aeration regime. Both decrease and increase in corrosion losses were observed, which indicated that the subdivision of microorganisms into destructors and passivators of corrosion is merely conventional.

[Initial stages of steel biocorrosion]. / Issledovanie nachal'nykh étapov biokorrozii stali.

Initial stages of corrosion of mild steel induced by Klebsiela rhinoscleromatis BO2 were studied in various media. The effect of the microorganism was detected 8-10 h after inoculation. The number of viable cells were virtually unchanged within one month in all media, but the corrosive activity of the strain decreased. The corrosive activity of microorganisms can be determined by spectrophotometry even only after incubation for 24 h. At a low level of organic substrate, even strong colonization with microorganisms does not inevitably result in a significant damage to metals.

[Chemical-microbiological diagnosis of stress-corrosive damage to pipelines]]. / Khimiko-mikrobiologicheskaia diagnostika stress-korrozionnykh povrezhdenii magistral'nykh truboprovodov.

Samples of soil, ground, electrolyte, corrosion products, and protective coating were taken after excavating pipelines. The depth of stress corrosion cracks of the pipe steel was mostly related to the numbers of sulfate-reducing and denitrifying bacteria. In certain types of soil, damage correlated with the number of acid-producing microorganisms and aerobic chemoorganotrophs (saprophytes). A correlation was found between the extent of stress-corrosion damage to pipelines and the contents of reduced iron, sulfides, and organic carbon in surrounding ground.

[Direct quantitative method for evaluating the effect of biocides on Pseudomonas fluorescens in different culture media]. / Priamoi kolichestvennyi metod otsenki deistviia biotsidov na Pseudomonas fluorescens na raznykh pitatel'nykh sredakh.

A method for quantitative evaluation of the effects of biocides is presented. The method was tested in experiments with Pseudomonas fluorescens grown on various agar nutrient media. The effective concentrations of biocides that decreased the maximum specific rate of the colony biomass growth (mu'm) were called S (suppressing) concentrations, and concentrations that decreased the number of colony-forming units (CFU) were taken as L (sublethal) concentrations. The efficiency of the reported approach was demonstrated in experiments with three biocides tested in four nutrient media. It was found that the biocide sensitivity of Pseudomonas fluorescens varied by a factor of 30, depending on the amount and the type of the nutrient substrate.

[Increase in the ecological danger upon the use of biocides for fighting corrosion induced by microorganisms]. / Povyshenie ékologicheskoi bezopastnosti pri ispol'zovanii biotsidov dlia bor'by s korroziei, indutsiruemoi mikroorganizmami.

Five synergistic combinations of biocides were found, among which the combination of kathon + copper sulfate was the most efficient against Serratia marcescens. Depending on the ratio of these biocides, the synergistic effect of this pair allowed 4-20-fold decreases in the effective concentrations. Combinations of biocides with salts (carbonates and phosphates) that facilitate passivation of steel were found, which considerably decreased the corrosion losses of mild steel in comparison to isolated treatment with biocides or salts. The data showed that biocides must be added to corrosion-prone systems simultaneously with the beginning of their exploitation. Otherwise, considerably excessive amounts of biocides or their synergistic compositions are needed.

[Development of biological methods of combating steel corrosion, induced by aerobic microorganisms]. / Razrabotka biologicheskikh metov bor'by s korroziei uglerodistoi stali, indutsirovannoi aérobnymi mikroorganizmami.

Cocultivation of degrading microorganisms and their antagonists decreases the corrosion loss of carbon steel by 20 to 80%. It was found that a microorganism can either accelerate or inhibit corrosion, depending on the nutrient. The magnitude of the effect on corrosion depends on the ability of the microorganism to respond to changes in the nutrient-medium composition by releasing acidic or alkaline metabolites.

[Simplified model of increase in colony diameter during growth of unicellular microorganisms and its use in evaluating the effect of biocides on microbial cells]. / Uproshchennaia model' rosta diametra kolonii odnokletochnykh mikroorganizmov i ee ispol'zovanie dlia otsenki vozdeistviia biotsidov na mikrobnye kletki.

A simplified model of increase in colony diameter is proposed. The model uses the size of single cells and several measurements of colony diameter during linear growth for calculating with good approximation the growth curve for the culture from the moment of inoculation. The parameter mu(m)', which is approximately 10% lower than the maximum specific growth rate of the colony biomass, could be also calculated. The effect of copper sulfate on the colony growth of Pseudomonas sp. G-1 was studied using the model. A high concentration of Cu2+ ions was found to result in decreases in the value of mu(m)', colony diameter, and the rate of increase in the colony diameter.

[Effect of physico-chemical properties of polyacrylamide gel media on the growth of Escherichia coli colonies]. / Vliianie fiziko-khimicheskikh svoistv gelevoi osnovy poliakrilamidnykh sred na rost kolonii Escherichia coli.

We studied the growth of Escherichia coli LE-392 colonies on polyacrylamide gels (PAAG) depending on the physico-chemical properties of the latter, i.e. polymer concentration in the gel, swelling degree, bound water content (fm), spin-lattice relaxation and spin-spin relaxation times of water molecule protons, and modulus of elasticity (G0). S- or R-type colonies formed depending on gel properties; the diametral growth rate of S colonies was 3 times less compared with that on the control agar medium (Tryptose broth). The procedure is proposed for preparation of PAAG which rules out syneresis. Functional relations between the polymer concentrations in uniformly swelling gels and concentrations of copolymers in the reaction mixture, fm and G0 were revealed. The fm and G0 parameters can be used for controlling the quality of PAAG.