BROAD-SPECTRUM AND MODE OF ACTION OF AN ANTIBIOTIC PRODUCED BY SCYTONEMA SP. TISTR-8208 IN A SEAWEED-TYPE BIOREACTOR

A photobioreactor was constructed using anchored polyurethane foam str ips (1 x 1 x 40 cm) fixed onto a stainless-steel ring to prevent flota tion, as a biomass support material (BSM). This type of reactor was na med a seaweed-type bioreactor. A filamentous cyanobacterium, Scytonema sp. TISTR 8208, which produces a novel cyclic dodecapeptide antibioti c, was immobilized in seaweed-type photobioreactor and cultivated with air containing 5% CO2 sparged at a gas flow rate of 250 mL/min under illumination at a light intensity of 200 mu mol photon m(-2) s(-1). Th e antibiotic produced in the seaweed-type photobioreactor was purified by HPLC and examined regarding its spectrum and mode of action. The a ntibiotic effectively inhibited the growth of Gram-positive bacteria, pathogenic yeasts, and filamentous fungi, but it had only a weak effec t on Gram-negative bacteria. Scanning electron micrograph analysis sho wed that the most characteristic change was swelling of the cells afte r exposure to the antibiotic. The antibiotic seems to alter the confor mation of the microbial cell membrane, thereby changing its permeabili ty, leading to osmotic shock.