Effect of low concentrations of caffeine and colchicine on microbial growth and biofilm formation

Abstract

A study into the effect of low concentrations of caffeine and colchicine alkaloids on the growth and biofilm formation of rhizospheric microorganisms – Gram-positive Rhodococcus qingshengii and Gramnegative Rhizobium radiobacter – is presented. Alkaloids present in plants effectively protect them from being eaten by animals of various taxa, as well as from fungal and bacterial infections. Forming part of a complex, evolutionary system of plant-microbial interactions, they occur naturally in the medium at low concentrations. One of the decisive factors in the spread of microorganisms is the formation of biofilms. In the study, alkaloids were added to the bacterial suspension at time intervals corresponding to distinct phases of biofilm formation. In order to determine the level of biofilm formation, bacterial cells were stained with crystal violet. The optical density of the suspension was used to assess the effect of alkaloids on bacterial growth and biofilm formation. The effect of caffeine and colchicine in concentrations of 10-5 g/L on the growth and biofilm formation of microorganisms is revealed for the first time. Although alkaloids did not affect the growth of the suspension of Gram-positive Rhodococcus qingshengii, they effectively suppressed the suspension of Gram-negative Rhizobium radiobacter. While Rhodococcus qingshengii showed greater sensitivity to alkaloids at the stage of biofilm formation, Rhizobium radiobacter was more sensitive at the stage of "mature" biofilms. The effect of alkaloids could be expressed both in terms of suppression and enhancement of biofilm growth. It can be assumed that the mechanism of action of plant alkaloids at the level of signaling systems and bacterial quorum sensing allows the protective function to be maintained even with a significant decrease in the number of alkaloids under conditions of permanent antagonism in which they are constantly being destroyed by phytopathogens.