Colonization of sugarcane by Acetobacter diazotrophicus is inhibited by high N-fertilization

Acetobacter diazotrophicus is a nitrogen-fixing endophytic bacterium, origi nally isolated from sugarcane. Its colonizing ability was evaluated in high and low N-fertilized sugarcane plants by inoculating stem-cuts with a beta -glucuronidase marked A. diazotrophicus strain. Bacterial quantification by the most probable number technique showed a severe decrease of A. diazotro phicus cells in plants fertilized with high levels of nitrogen. The inocula ted strain was detected inside low N-fertilized sugarcane plants by histoch emical staining of beta-glucuronidase and scanning electron microscopy. A. diazotrophicus was found mainly inside cortical cells of stems and inside x ylem vessels. No beta-glucuronidase activity was observed in non-inoculated plants. High nitrogen fertilization of fields might be a threat to maintai ning naturally occurring endophytic associations. (C) 1999 Federation of Eu ropean Microbiological Societies. Published by Elsevier Science B.V. All ri ghts reserved.