Endoglucanases from Paenibacillus spp. form a new clan in glycoside hydrolase family 5.

Endoglucanase (Egl)-producing bacteria from soil samples were screened using insoluble cellulosic substrates as sole carbon sources at alkaline pH (pH 9–10). Four Egls with Avicelase activity at alkaline pH were found in the culture broth of each isolate. The Egl genes of the isolates (all Paenibacillus spp.) were shotgun cloned and sequenced—all had a 1752bp open reading frame (584 amino acids) with a putative signal sequence (33 amino acids), and encoded mature enzymes of 551 amino acids (58,360–58,672Da). The mature enzymes showed a high degree of similarity to each other (>93% identity), with the next closest similarity to Egl3a of a patented strain of Paenibacillus lautus NCIMB 40250 (81.5–87.3% identity). These enzymes showed low similarity to other known Egls with less than 50% identity. A representative recombinant enzyme degraded lichenan, carboxymethylcellulose (CMC), glucomannan, acid or alkaline swollen celluloses, and microcrystalline cellulose (Avicel). The optimal pH and temperature of the recombinant enzyme for degrading CMC and Avicel were pH 6.0–8.5 and 45–55°C, respectively. Egls belong to glycoside hydrolase family 5 and form a distinct clan based on the phylogenetic analysis of their amino acid sequences.