Sustainable production of cellulase by soil bacterium Sinorhizobium meliloti using commercial and agroindustrial waste substrates

Abstract

Cellulases are industrially important enzymes which can convert the most abundant natural polysaccha-ride - cellulose into glucose, making it as a renewable resource of carbohydrate for the obtaining of bio-based products and bioenergy. The latest trends in microbial cellulase production include the use of various waste products for the microorganism‘s growth, especially of agroindustrial origin, within the solid-state fermentation (SSF), as a promising technology that can potentially reduce the overall costs. Among soil bacteria, rhizobia are rarely investigated as a cellulase producer. The rhizobial soil bacte-rium Sinorhizobium meliloti strain 224 was able to grow and express the metabolic activity on the commercial substrate carboxymethyl cellulose (CMC), but also cellulose based waste materials, such as soybean stems and oat dust. The cellulase produced in a liquid medium with commercial substrates, containing 0.1% (w/v) of CMC in yeast mannitol broth and 10% of the inoculum, after 48 h of incuba-tion, at 28 °C, expressed maximum Avicelase activity of 0.077 U/mL. On the other side, the cellulase produced in a medium with waste substrates, containing 1 g of soybean waste with 10% of the inocu-lum, after 48 h of incubation, at 28 °C, expressed maximum Avicelase activity of 1.295 U/g. The hy-drolysis of Avicel indicate a pre-dominant activity of exoglucanases, those produce the glucose, with traces of other soluble sugars, showing that the crude enzyme, produced on waste material using the soil bacteria S. meliloti 224, could be used in eco-friendly processes of cellulose bioconversion and reduction of biological waste.