Research objective is the assessment of toxicity level of ruminal fluid of cattle with use of indicator luminescent strains of bacteria developed on the basis of E. coli. According to the research results systemic toxic action of ruminal fluid with use of sensory bacterial strains with constitutive luminescence (E. coli K12 TG1 with clone luxCDABE genes Photobacterium leiognathi 54D10) were assessed. During the contact of native ruminal fluid with sensory luminescent bacteria E. coli dose-dependent inhibition of luminescence in the first seconds of contact was registered. However, by the second minute of contact quenching was up to 5.20±0.59% in baseline environment and decreased after two-time dilution procedure up to 102.56±4.83% with dilution 1:1024). After 30 min of incubation of mixture level of luminescence in the sample with native ruminal fluid reached the control level and over time it increased to 190.59±22.15% after 60 min of contact. Strain E. coli katG::lux, where the cloned promoter is responsible for the synthesis of catalase providing the neutralization of hydrogen peroxide demonstrated luminescence induction of 3.0 relative units at the 60th minute of contact. Study of genotoxic effects based on activation of repair proteins RecA/LexA using strain E. coli recA::lux, allowed to register luminescence inducing effects of the bacterial cells in contact with native rumen fluid.
A way to assess the metabolic state of bacteria of rumen microflora cells is the registration of glow kinetics including recombinant strains, which is a reflection of stress states developing in the cell. The experiment evaluated the effect of rumen fluid in combination with probiotic strains and vanillin on the luminescence of a recombinant strain Escherichia coli MG1655 and digestibility of feed. The “in vitro” method with the rumen simulation technique (Rusitec) was used to determine the digestibility of the dry substance of feed. Using the initial sample, the glow level at the 30th minute was recorded at 3,149±145 RLU, which is 32% of the control level. In the presence of rumen fluid (at the concentration of 6.25%), there was observed an improved response by E.coli against Saccharomyces boulardii’s background (by 44%). The use of vanillin in rumen fluid increases the glow level of bacterial cells in the range of concentrations up to 50%, and in combination with probiotic strains, in the range of 25-50 %. In vitro conditions against the background of rumen fluid showed that vanillin in combination with probiotic strains Bifidobacterium longum and Bifidobacterium adolescentis / Lactobacillus acidophilus contributes to an increase in the digestibility of the dry substance of feed.
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