Nitrosonium Cation NO⁺ Inhibits Nitric-Oxide Functions in the Regulation of Pseudomonas aeruginosa Biofilm Formation

Abstract

The structure of nitric oxide (NO) donors, paramagnetic dinitrosyl iron complexes with SH ligands (DNICs), contains two nitrosyl groups, NO and NO⁺, which are released from a DNIC upon degradation in the cell. The selective ability of diethyl dithiocarbamate (DETC) to bind NO was used in this work to study the functions of nitrosonium cation NO⁺ in the regulation of biofilm formation by nitric oxide donors. The combined treatment of Pseudomonas aeruginosa with DETC and NO donors, sodium nitrite NaNO₂ or binuclear DNIC with glutathione (B-DNIChglu), multiply reduced the biofilm formation relative to the control and single treatments with each compound. The biofilm formation depended on the ratio of components. At a tenfold excess of DETC against DNICglu, the formation rate decreased by three times, and under a fivefold excess, by 1.8 times. The stable [Fe²⁺–DETC] complex formed during the combined treatment functioned as an NO trap, leading to the block in the synthesis of the signaling regulator DNICglu from NO and iron and to the accumulation of nitrosonium cation NO⁺ in the cell. The maximum decrease in the biofilm formation rate was established in the option with successive treatment of cells with DETC with a lag period of 40 min after the introduction of the NaNO₂ donor and the formation in DNIC with thiosulfate ligands, universal NO signaling molecules of all biosystems, in the cells. The results obtained expand knowledge about the functions of nitrosonium cation and contribute to the disclosure of mechanisms of the toxic activity of DNIC donors. They correlate with our earlier results on NO⁺ inhibition of E. coli colony formation in experiments with DNICglu, as well as with the data of other researchers obtained on yeast and in MCF7 cancer cell culture.