Cloning and Comparison of Third β-Glucoside Utilization (bglEFIA) Operon with Two Operons of Pectobacterium carotovorum subsp. carotovorum LY34

Abstract

A third bgl operon containing bglE, bglF, bglI, and bglA was isolated from Pectobacterium carotovorum subsp. carotovorum LY34 (Pcc LY34). The sequences of BglE, BglF, and Bgll were similar to those of the phosphotransferase system (PTS) components IIB, IIC, and IIA respectively. BglF contains important residues for the phosphotransferase system. The amino acid sequence of BglA showed high similarity to various 6-phospho-β-glucosidases and to a member of glycosyl hydrolase family 1. Sequence and structural analysis also revealed that these four genes were organized in a putative operon that differed from two operons previously isolated from Pcc LY34, bglTPB (accession no. AY542524) and ascGFB (accession no. AY622309). The transcription regulator for this operon was not found, and the EII complexes for PTS were encoded separately by three genes (bglE, bglF, and bglI). The BglA enzyme had a molecular weight estimated to be 57,350 Da by SDS–PAGE. The purified β-glucosidase hydrolyzed salicin, arbutin, ρNPG, ρNPβG6P, and MUG, exhibited maximal activity at pH 7.0 and 40 °C, and displayed enhanced activity in the presence of Mg²⁺ and Ca²⁺. Two glutamate residues (Glu₁₇₈ and Glu₃₇₈) were found to be essential for enzyme activity.

• Pectobacterium carotovorum subsp. carotovorum LY34
• bgl operon
• PTS system
• 6-phospho-β-glucosidase