This is the first report that Lysobacter fixes nitrogen under free-living conditions, as shown by its ability to grow on nitrogen-free medium and accumulate relatively high amounts of ammonia in the culture broth. Growth of the E4 Lysobacter strain, isolated in a screen for nitrogen-fixing and ammonia-producing bacteria, resulted in higher ammonia accumulation (0.53 mM ammonium ion concentration) in media containing glucose rather than other tested carbon sources. The optimum glucose concentration was 0.30% at an initial medium pH of 7.0 and incubation temperature of 30 degrees C. From time-course experiments, when the glucose in the culture was exhausted, ammonia began to be accumulated, and maximum ammonia accumulation (similar to 1.60 mM) was reached after 8 days of incubation. Ammonia accumulation by this strain required molybdenum, manganese, and iron. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.