Otimização dos parâmetros de produção de biomassa de Azospirillum amazonense (BR- 11145) para incorporação em inoculantes agrícolas

Abstract

The Azospirillum amazonense, is a gram-negative rhizobacteria associated with various grasses, provides plant growth due to their ability to synthesize various phytohormones (IAA), siderophores and polysaccharides, and currently it composes the EMBRAPA’s mixed inoculant for sugarcane. This study aimed to select and optimize culture media and processing parameters for the pilot scale cultivation of A. amazonense BR-11145 besides replacing carbon sources in order to obtain a reproducible medium and low-costs process. It was performed a screening of DYGS medium components. The experiment was conducted in a rotatory incubator at 30°C and 150 rpm through 4 fractional factorial design (27-3, two 26-3 and 25-2) in three different levels of carbon, nitrogen and minerals sources (regular, +50% and - 50% w/w). It was obtained a simplified medium costing R$1,70 per liter, 1/3 of the original value, and a increase of 66,7% in the biomass production capacity (medium composition: glucose 5.0 g/L; yeast extract, 3.0 g/L; K2HPO4 0.25 g/L, MgSO4 0.75 g/L and micronutrients 4.0 mL/L).To determine the best culture condition, a DCCR 23 was carried out in a bioreactor from which the conditions defined were: temperature 35°C, agitation 250 rpm and aeration of 8.0 Lpm. The process kinetics was studied using three carbon sources obtaining the parameters described below: glucose 10 g/L (X = 5,737 g/L, PX = 0,315 g/L.h, µx = 1,253, IC = 31,79 mM, PIC = 1,257 mM.h-1); glycerol 10 g/L (X = 7,136 g/L, PX = 0,471 g/L.h, µx = 1,482, IC = 38,194 mM, PIC = 1,805 mM.h-1); sucrose 10 g/L (X = 7,966 g/L, PX = 0,717 g/L.h, µx = 1,472, IC = 85,833 mM, PIC = 6,944 mM.h-1). In all cases, the production cost of R$ 0.32 per gram of biomass were found. According to results for biomass and indolic compounds production capacity, it is recommended the use of sucrose for cultivation of A. amazonense BR-11145.