We studied the influence of Bacillus cereus bacteria on cells of the freshwater alga Chara corallina. These bacteria
and recombinant Bacillus subtilis strains are capable of producing the secreted toxin HlyII, which
changes the electrophysiological parameters of the algal electrically excitable plasma membrane by forming
pores. Cooperative incubation of bacterial cells, which carry active hlyII gene, and Chara corallina cells caused
a decrease in the resting potential (Vm) and plasma membrane resistance (Rm) of algal cells. The efficiency of
each strain was commensurable with its ability to produce HlyII. Purified hemolysin II caused a similar effect
on Vm and Rm of intact and perfused cells. This protein changed the kinetics and magnitude of transient
voltage-dependent calcium and calcium-activated chloride currents owing to the formation of additional
Ca2+-permeable pores in algal cell membrane. Occurrence of the cellulose cell wall with pores 2.1 to
4.6 nm in diameter suggests that HlyII molecules reach the plasma membrane surface strictly as monomers.
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