[Azomonas agilis in the surface water of the environs of Buenos Aires].

In 1941, it was reported the presence of Azomonas agilis in rivers near Buenos Aires City. To our knowledge no other study has been carried out since then, so that the object of this paper was to investigate some characteristics of this organism and its possible influence on the nitrogen balance in waters. The isolation was performed by the plate method, using a mineral base for Azotobacter with different energy sources. Calcium malate appeared to be the best for Azomonas-like organisms. On pure cultures were performed tests to describe the main properties. All the organisms isolated had similar morphology, big cells 3 x 5 mu, individuals or sometimes in pairs, with intracellular granules and Gram negative. Cysts were not formed and motility was very intense in all cases. Physiologically they all were strictly aerobic, catalase positive and able to reduce acetylene so it was confirmed they belonged to the genus Azomonas. Some of them could use glucose and produced a water soluble green pigment, fluorescent under ultraviolet light which are the main characteristics of Azomonas agilis. Others lacked one of this properties but also were considered to be this species because they were very different from Azomonas insignis. One strain remained labelled only as Azomonas sp because it did not show characters of any of the two species. Estimations of bacterial density by most probable number method indicated that this was very low and by using a colorimetric determination for ethylene no nitrogenase activity could be detected in the river water, adding or not glucose even after 48 h of incubation.(ABSTRACT TRUNCATED AT 250 WORDS)