Metabolism of the phosphonate herbicide glyphosate by a non-nitrate-utilizing strain of Penicillium chrysogenum

A Penicillium chrysogenum strain was isolated for its ability to grow in mi nimal medium containing the herbicide glyphosate as the only nitrogen sourc e. The presence of concentrations up to 25 mM progressively stimulated the fungal growth rate, which was negligible in media lacking reduced nitrogen. However, glyphosate utilization never exceeded I mmol g(-1) mycelial dry m ass, and below a threshold concentration both herbicide uptake and fungal g rowth were subject to a lag phase, suggesting that the herbicide may enter the cell by either simple passive diffusion or inducible carriers. Amino ac ids, possible products of glyphosate breakdown, as weft as ammonia, were fo und to replace the herbicide in restoring mycelial growth. Cells were devoi d of detectable nitrate reductase activity, thus the isolate seems to be im paired in its ability to convert nitrate to ammonium. In vitro activity of 5-enol-pyruvyl-shikimate-3-phosphate synthase, the target site of glyphosat e action, was highly sensitive to the herbicide. Fungal growth rate was con siderably lower when the herbicide was also the only phosphorus source, whe reas glyphosate utilization was substantially unaffected, suggesting an unu sual route for its degradation. Herbicide metabolism was strongly reduced w hen other sources of organic nitrogen were made available. (C) 2001 Society of Chemical Industry.