Low-temperature-active and salt-tolerant β-mannanase from a newly isolated Enterobacter sp. strain N18

• We described a high-active and stable extracellular β-mannanase produced by a novel mannanase-producer Enterobacter sp. strain N18.
• The mannanase-producer was obtained by high-throughput screening method.
• The β-mannanase is able to decrease the viscosity of guar gum solution in a very short time which implies the potential for serving as a gel-breaker.
• The β-mannanase is characterized by a broad working temperature especially low temperature, salt-tolerance and wide working pH range.

A low-temperature-active and salt-tolerant β-mannanase produced by a novel mannanase-producer, Enterobacter sp. strain N18, was isolated, purified and then evaluated for its potential application as a gel-breaker in relation to viscosity reduction of guar-based hydraulic fracturing fluids used in oil field. The enzyme could lower the viscosity of guar gum solution by more than 95% within 10 min. The purified β-mannanase with molecular mass of 90 kDa displayed high activity in a broad range of pH and temperature: more than 70% of activity was retained in the pH range of 3.0–8.0 with the optimal pH 7.5, about 50% activity at 20°C with the optimal temperature 50°C. Furthermore, the enzyme retained >70% activity in the presence of 0.5–4.0 M NaCl. These properties implied that the enzyme from strain N18 had potential for serving as a gel-breaker for low temperature oil wells and other industrial fields, where chemical gel breakers were inactive due to low temperature.