Reversal by Histidine of the Inhibition of Prototheca Growth due to 3-Amino-1,2,4-triazole

Abstract

3-AMINO-l,2,4-triazole (amitrole) is used as a systemic herbicide. It also inhibits the growth of a number of micro-organisms including several algae. Organic acids have long been known to inhibit the growth of algae by combining with iron1. Aaronson2 concluded that amitrole was also working in this way as the inhibition of Ochromonas danica could be abolished by the supply of extra iron to cultures in the presence of the inhibitor. Later Wolf3, examining Chlorella pyrenoidosa, and Boney4 certain marine red algae, reported that the inhibition by amitrole could be reversed by adenine. In this the algae are similar to Escherichia coli5. Histidine is effective in releasing the inhibition of Torula cremoris5 and of Saccharomyces cerevisiae6. Since the standard medium used by Aaronson contained histidine7, an investigation of the reversal of amitrole toxicity towards Prototheca zopfii was carried out. This colourless alga is believed to be closely related to Chlorella and it will grow in a mineral medium supplemented with glucose and thiamine8. Aaronson and Scher7 showed that there was no significant difference in the concentration of amitrole required to achieve inhibition of Euglena and Ochromonas growth in the presence of an organic substrate in the dark as compared with the light although chlorophyll synthesis was inhibited.