Antimycobacterial and cytotoxicity activity of microcystins.

Background: The present work aimed to evaluate the antimycobacterial activity and cytotoxicity of Microcystis aeruginosa toxins, the MC-LR variant and purified extract of [D-Leu(1)] microcystin-LR.

Methods: The antimicrobial activity of M. aeruginosa extract and microcystin was evaluated by resazurin microtiter assay against Mycobacterium tuberculosis, M.

Microcystin-LR: How it affects the cardio-respiratory responses to hypoxia in Nile tilapia, Oreochromis niloticus.

The effects of microcystin on the cardio-respiratory function of Nile tilapia were analyzed 48 h after intraperitoneal injection of microcystin-LR (MC-LR - 100 μg kg(-1)body weight). Exposure to MC-LR induced significant reduction in metabolic rate (VO(2)) and increase in the critical O(2) tension (P(C)O(2)) in relation to the control group. Gill ventilation (V(G)) and ventilatory tidal volume (V(T)) were considerably lower in fish exposed to MC-LR, probably due to an alteration in the homeostatic mechanisms, impairing the regular respiratory response of this species to environmental hypoxia.