[Dynamics of microbial populations in the biofilm on protective coating].

Dynamics of microbial populations in the biofilm on the surface of protective coating Poliken 980-25 has been studied. It was shown that in the process of succession one can observe some changes of taxonomic composition of biofilm bacteria. Bacteria of Pseudomonas genus were revealed at early stages of succession, they reduce Fe+3 and oxidize carbohydrates. Bacteria of Arthrobacter genus begin developing 2 hours after the exposure, Bacillus genus bacteria appear 6 hours after the experiment beginning. It should be noted that iron-renewing bacteria as dominants in the biofilm are the agents ofbiolesion of not only protective material but also metal.

[Microbial biofilms on protective coatings of underground metal structures].

Biofilms are highly organized groupings which are formed by microorganisms of one or several species and consist of actively functioning cells, those at rest as well as of the forms which are not cultivated. The survey includes data concerning formation of biofilms and factors affecting the process of their development. The paper deals with the mechanisms of biofilms formation in bacteria and with the methods connected with obtaining and studying mutants of bacteria imperfect as to biofilms formation. The role of exopolymers in the structure and function of biofilms is discussed.

[Adhesion of sulphate-reducing bacteria to steel under cathode polarization].

Adhesion of different (as to their corrosion aggression) strains of sulphate-reducing bacteria to steel has been studied under cathode polarization at various potentials: -800, -900, -1000, -1200 mV. It has been established that cathode polarization differently affects the adhesion of strain of sulphate-reducing bacteria with various aggression to steel. Correlation between the bacterial strains aggression and the number of cells adhered to metal have been noted. The cells of aggressive strains of D. indonensis Indonesia and Desulfovibrio sp. Kiev-10 adhered to metal most actively at cathode depolarization (8.0 x 10(7) and 3.5 x 10(7) cell/cm2, respectively). Nonaggressive strains of bacteria D. desulfuricans Kiev-45 and Desulfobulbus sp. Portsmouth adhered to metal in a less quantity. The data obtained prove that the use of cathode protection without allowance for the microbe factor can lead to intensification of the corrosion process.

[Effect of corrosion inhibitor on adhesion of sulfate-reducing bacteria to steel and their production of exopolymer complex]. / Vlyv inhibitora koroziï na adheziiu do stali sul'fatvidnovliuval'nykh bakterii ta produkuvannia nymy ekzopolimernoho kompleksu.

It was shown in the laboratory investigations that the cells of sulphate-reducing bacteria of both aggressive Desulfovibrio sp. strain Kiev-10 and nonaggressive Desulfovibrio desulfuricans strain Kiev-45 strains can produce exopolysaccharides (EPS). Plankton (freely floating) cells of sulphate-reducing bacteria produce greater quantity of EPS than the cells of the biofilm formed on steel. The inducing effect of metal on EPS synthesis by sulphate-reducing bacteria has been established. The content of carbohydrates in EPS is higher in the biofilm of aggressive strain Desulfovibrio sp. Kiev-10 than in plankton bacteria as well as compared with the biofilm of less aggressive strain Desulfovibrio desulfuricans Kiev-45. Specific production of EPS of the aggressive strain in the biofilm formed on the steel is 3 orders higher than in the plankton cells. It has been established that the quantity of cells of sulphate-reducing bacteria adhered to steel decreases in the presence of the corrosion inhibitor N-decylpyridinium chloride (high-molecular compound of nitrogen-including PAR of the cationic type). It is shown that EPS synthesis is blocked in the biofilm formed by sulphate-reducing bacteria on steel under the effect of the corrosion inhibitor, while EPS production in plankton is stimulated.