Recombinant expression and characterization of an acid-, alkali- and salt-tolerant β-1,3-1,4-glucanase from Paenibacillus sp. S09

A new β-1,3-1,4-glucanase gene (PlicA) was cloned from Paenibacillus sp. S09. The ORF contained 717 bp coding for a 238 amino acid protein. PlicA, expressed in Escherichia coli and purified by Ni²⁺-affinity chromatography, had optimum activity at 55 °C and pH 6.2. The specific activity toward barley β-glucan reached 7,055 U/mg. K ₘ and V ₘₐₓ values with barley β-glucan were 3.7 mg/ml and 3.3 × 10³ μmol/min mg, respectively. The enzyme exhibited acid- and alkali-tolerance with more than 80 % activity remaining after incubation for 4 h at pH 3.5–12. PlicA was salt-tolerant (>90 % activity retained in 4 M NaCl at 25 °C for 24 h) and salt-activated: activity rising 1.5-fold in 0.5 M NaCl. The thermostability was improved by NaCl and CaCl₂. This is the first report of an acid-, alkali- and salt-tolerant bacterial β-1,3-1,4-glucanase with high catalytic efficiency.