Title

Molecular adaptation to environmental temperature: Comparison of glutamine synthetases from psychrophilic, psychrotolerant, and mesophilic members of the Alteromonadaceae

Date of Completion

January 2004

Keywords

Biology, Microbiology

Degree

Ph.D.

Abstract

The biochemical adaptation of glutamine synthetase (GS) to environmental temperature was investigated within the family Alteromonadaceae. The glnA genes encoding glutamine synthetase were sequenced from six bacterial strains that differed in optimal growth temperatures: Moritella sp. strain Ant-300 (7°C), Shewanella benthica (10°C), Moritella marina (15°C), Shewanella hanedai (21°C), Pseudoalteromonas haloplanktis (28°C), and Alteromonas macleodii (36°C). Recombinant GSs from the psychrophiles, M. Ant-300 and M. marina, and the mesophile A. macleodii were purified to homogeneity from a recombinant expression system using an E. coli glutamine auxotroph that also lacked the regulatory adenylylation system. The kinetic parameters were determined for the unadenylylated GSs using the biosynthetic assay. The GSs from the psychrophiles displayed higher catalytic activities at low temperatures and were less thermally stable compared to A. macleodii GS. However, the catalytic activities of the different GSs were comparable at the optimal growth temperature of the organism. These results suggest that, even though the enzymes are highly conserved, they each exhibit distinctive responses to environmental temperature that may be ascribed to the alterations in the amino acid sequence. ^