Regulation of capsular polysialic acid biosynthesis by temperature in Pasteurella haemolytica A2

The capsular polysaccharide of Pasteurella haemolytica A2 consists of a linear polymer of N-acetylneuraminic acid (Neu5Ac) with α(2–8) linkages. The production of this polymer is strictly regulated by the growth temperature and above 40°C no production is detected. Analysis of the enzymatic activities directly involved in its biosynthesis reveals that Neu5Ac lyase, CMP-Neu5Ac synthetase and polysialyltransferase are involved in this regulation. Very low activities were found in P. haemolytica grown at 43°C (at least 25 times lower than those observed when the growth temperature was 37°C). The synthesis of these enzymes increased rapidly when bacteria grown at 43°C were transferred to 37°C and decreased dramatically when cells grown at 37°C were transferred to 43°C. These findings indicate that the cellular growth temperature regulates the synthesis of these enzymes and hence the concentration of the intermediates necessary for capsular polysaccharide genesis in P. haemolytica A2.