Isolation and Characterization of a New Superior Lactobionic Acid-Producing Bacterium, Enterobacter cloacae KRICT-1, from Environmental Soil Samples

Abstract

Lactobionic acid (LBA) is a specialty aldonic acid that has been broadly employed in various industries, including food, cosmetics, and pharmaceuticals. In this study, we isolated a new excellent LBA-producing bacterium from soil, designated as strain KRICT-1. A phylogenetic analysis revealed that this strain was identified as Enterobacter cloacae. Previously, we successfully produced LBA using Pseudomonas taetrolens, an excellent LBA-producing bacterium. In a flask culture at 30 °C, E. cloacae KRICT-1 showed the same LBA production concentration (209.3 g/L) and yield (100%) from 200 g/L lactose, compared with those obtained from P. taetrolens cultivated at 25 °C, the growth temperature of which showed the highest LBA production ability. E. cloacae KRICT-1 exhibited an approximately 1.08-fold higher LBA productivity (8.37 g/L/h) than that (7.75 g/L/h) of P. taetrolens, indicating that E. cloacae KRICT-1 was a more efficient LBA-producing bacterium than P. taetrolens. The LBA productivity of E. cloacae KRICT-1 further improved to 8.72 g/L/h at 35 °C. Furthermore, the LBA productivity (9.97 g/L/h) improved at 35 °C in a 5 L fermenter. After whole-genome sequencing of E. cloacae KRICT-1, we found that two quinoprotein glucose dehydrogenases (GDH1 and GDH2) from this strain could produce LBA from lactose by recombinantly expressing these genes in Escherichia coli. Our present results clearly demonstrated that E. cloacae KRICT-1 can be a new promising host for the industrial production of LBA.