Abstract

β-Galactosidase is extensively employed in the manufacture of dairy products, including lactose-reduced milk. Here, we have isolated two gram-negative and rod-shaped coldadapted bacteria, BS 1 and HS 39. These strains were able to break down lactose at low temperatures. Although two isolates were found to grow well at 10°C, the BS 1 strain was unable to grow at 37°C. Another strain, HS-39, evidenced retarded growth at 37°C. The biochemical characteristics and the results of 16S rDNA sequencing identified the BS 1 isolate as Rahnella aquatilis, and showed that the HS 39 strain belonged to genus Buttiauxella. Whereas the R. aquatilis BS 1 strain generated maximal quantities of β-galactosidase when incubated for 60 h at 10°C, Buttiauxella sp. HS-39 generated β-galactosidase earlier, and at slightly lower levels, than R. aquatilis BS 1. The optimum temperature for β-galactosidase was 30°C for R. aquatilis BS-1, and was 45°C for Buttiauxella sp. HS-39, thereby indicating that R. aquatilis BS-1 was able to generate a cold-adaptive enzyme. These two cold-adapted strains, and most notably the β-galactosidase from each isolate, might prove useful in some biotechnological applications.

• Keywords: cold-adapted; β-galactosidase; Rahnella aquatilis; Buttiauxella sp.