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The effects of a herbicide butachlor[2-chloro-2´,6´-diethyl-N-(butoxymethyl) acetanilide] on the growth of the purple non-sulfur bacteria were investigated. The butachlor inhibited the growth of all species tested by 18-51%, except Rhodospirillum rubrum at concentrations of 10-´ M, which would be field capacity. The photosynthetic growth rate of the species in the presence of butachlor was influenced by the nitrogen source. Cultures supplied with (NH,)ZSO, showed a somewhat higher growth rate than those fixing dinitrogen, but they were more susceptible to butachlor (26-51%). On the contrary, butachlor enhanced the growth rate of Rhodospirillam rubrum in nitrogen gas conditions. When the culture was performed in medium with butachlor as the carbon source, the cells of fixing dinitrogen showed a higher exhaustion of butachlor than those supplemented with (NH)2SO4, which exhaustion was examined by a decrease of the major absorbance at 213 nm and 260 nm. The exhaustion of butachlor as the carbon source had relation with the growth of the cells. The alkalization of culture supplemented with nitrogen gas was found in the cells treated with butachlor or untreated. The butachlor affected the carotenoid region but bacteriochlorophyll remained unaffected.
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