Culture Optimization for Mass Production of <i>Rhizobium</i>Using Bioreactor Made of Readily Available Materials and Agitated by Air Flow

Large quantities of Rhizobium leguminosarum by conventional technique are a time-consuming and labor-intensive method of production. The selection of different types of nutrient media for the production of large amounts of rhizobium at low cost, determination of environmental regulators of culture medium and the effect of different levels of air flow into nutrition media have been investigated. Rhizobium cultured in modified air lift bioreactor as improved conventional system using Yeast Extract Mannitol Broth by assessing aeration and agitation in their submerged growth. For selection of suitable nutrient media for Rhizobium before mass production, YMA (Yeast Mannitol Agar), YSA (Yeast Sucrose Agar), YMA + bromthymol blue (BTB), YMA + Congo red (CR) medium was tested. To optimize the growing conditions of different temperatures, pH levels and salt strengths were investigated. Three air flow speeds at the rate of 0.01, 0.05 and 0.1 VVM for oxygen supply were ensured. A thick off-white bacterial colony was observed on the YMA plate among different culture media. Room temperature (25˚C - 30˚C), neutral pH (7.0), low salinity (1%) was observed to be suitable among the environmental conditions for Rhizobium mass production. The maximum density of Rhizobium was observed using air supply of 0.1 VVM level in bioreactor system. The result seemed that the air supply and agitation was an important growth factor in submerged cultivation. This study provides useful information on large scale production of Rhizobium of interest employing low cost effective modified air lift bioreactor within less time.