Effect of exudates excreted by Trichoderma harzianum on the nitrogen fixation (C2H2- reduction) rate of the cyanobacteria Anabaena variabilis

Abstract

Abstract Exudate of the fungus Trichoderma harzianum stimulate the nitrogen fixation (C2H2-reduction) of the cyanbacteria Anabaena variabilis. Autoclaving the exudates caused a decrease in the stimulation of the nitrogenase activity.Chemical analysis of the exudates showed it contain 95µg ml-1 protein, no free amino acids were detected, no nucleotides or nucleosides were found. Acid hydrolysis of the exudates showed the presence of bound amino acids and ammonia. Low concentrations (one n mole ml-1 ) of glutamic acid, aspartic acid, valine, glycine , and serine enhanced the nitrogenase activity and increased the heterocyst frequency of the cyanobacteria while threonine and proline seemed to reduce (inhibit) the nitrogenase activity at the same concentration.