Submerged Fermentation and Kinetics of Newly Isolated Priestia megaterium for the Production of Biopolymer Curdlan

Abstract

In this study, a curdlan-producing bacterium was isolated from Cow pea soil and identified as Priestia megaterium based on 16 S rRNA sequencing. To identify the most suitable carbon and nitrogen sources for curdlan production, submerged fermentation studies with different sources was carried out. To enhance the curdlan yield, optimization by one-factor-at-a-time approach was conducted. The optimal fermentation media consisted of 15% (w/v) sucrose, 0.1% (w/v) urea, 0.1% (w/v) KH2PO4, 0.04% (w/v) MgSO4·7H2O, trace elements, initial pH of 7.0 with 10% (v/v) inoculum size and agitation speed of 180 rpm. Kinetics of growth, curdlan yield, sucrose and ammonia depletion were studied for a period of 168 h. Maximum curdlan yield (0.31 g/L) was achieved at 96 h of fermentation. At this point, the fermentation media had an optical density of 9.68, biomass concentration of 4.26 mg/mL, and viable count of 2.4 × 104 CFU/mL. Additionally, the maximum percentage consumption of sucrose and ammonia over 168 h of fermentation were 75 and 62.5%, respectively. Finally, the identity of biopolymer curdlan was validated through characterization techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Thermogravimetric analysis (TGA). Some characteristic features of curdlan such as the β-1,3-linkage was depicted by the absorption band at 890 cm−1 in FTIR, flaky granules with irregularities as seen in SEM, and thermal degradation between 235 and 350 °C by TGA. To the best of our knowledge, this is the first report on curdlan production from Priestia megaterium.