ABILITY OF NITROGEN-FIXING BACTERIA TO EXCRETE AMMONIUM ISOLATED FROM MAIZE RHIZOSPHERE

Abstract

Nitrogen-fixing bacteria are bacteria that have an important role in the process of nitrogen assimilation in the soil. Nitrogen-fixing bacteria consist of symbiotic and non-symbiotic nitrogen-fixing bacteria found abundantly in the rhizosphere. This research seeks to isolate, characterize, and evaluate the ability of rhizosphere bacteria in maize on tropical marginal soils to excrete ammonium. Isolate nitrogen-fixing bacteria using nitrogen-free bromothymol blue (NFB) medium. Soil samples were inoculated on solid NFB medium using the spread method and then incubated at 30˚C  for 6-7 days to observe nitrogen-fixing bacterial growth and were then characterized. The physiological characteristics of nitrogen-fixing bacterial isolates from the maize rhizosphere that were observed include temperature, pH, and salinity. A temperature resistance test was conducted to determine the resistance of nitrogen-fixing bacterial isolates to temperature. Ammonium excretion test using the spectrophotometric method. Six nitrogen-fixing bacteria isolates had been identified molecularly were Rhizobium pusense (LC585441.1), Beijerinckia fluminensis (MG547695.1), Microbacterium neimengense (LC430078.1), Microbacterium binotii (MN428150), Rhizobium pusense (MK542929.1) and Rhizobium sp. strain FNF3 (MH910714.1). The results of the ammonium excretion test showed that the highest concentration was produced by Microbacterium binotii at 42.0 μM, Microbacterium neimengense at 41.0 μM while for Beijerinckia fluminensis species, Rhizobium sp strain FNF3, and 2 Rhizobium pusense isolates respectively 38.8 μM, 38.6 μM, 38.0 μM, and 36.2 μM.