Optimization of cold-active CMCase production by psychrotrophic Sphingomonas sp. FLX-7 from the cold region of China

Organic solid waste consists of 70 % biodegradables, such as cellulose, which is unable to be degraded quickly and efficiently in the cold region of China. Psychrotrophic cellulose-degrading bacteria play an important role in cellulose degradation at low temperatures. In this study, a psychrotrophic cellulose-degrading FLX-7 strain with high carboxymethyl cellulase (CMCase) activity was isolated from the soil of a solid waste landfill under the environmental temperature of −10 °C. The FLX-7 strain was identified as Sphingobacterium sp. based on morphology and physiological and biochemical properties as well as 16S rRNA gene sequence analysis. To improve the cold-active CMCase production of FLX-7, fermentation conditions were optimized using response surface methodology based on a Box–Behnken design. The maximum CMCase activity (16.95 U/mL) was obtained at optimal fermentation conditions (inoculum size 2.1 %, temperature 10.4 °C, incubation time 73.5 h, and pH 7.2). The optimum pH and temperature for enzymatic reaction of cold-active CMCase were 5.0 and 25 °C, respectively. The cold-active CMCase was stable at a wide pH range of 5.0–9.0 and temperature range of 10–30 °C. The FLX-7 strain could be distributed via a psychrotrophic cellulose-degrading strain library and applied more broadly to organic solid waste composting in cold regions.