Functional characterization of Bacillus cereus acyl-lipid desaturases

LORENA CHAZARRETA CIFRE; DIEGO DE MENDOZA; SILVIA ALTABE

Potrero de los Funes

Congreso; XLVII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2011

Fatty acid desaturases are responsible for the insertion of double bonds into fatty acids in reactions that require O2 and reducing equivalents. They play an important role in Bacilli cells to maintain membrane fluidity in response to a decrease in growth temperature. After cloning and functional characterization of two identified genes (BC2983 and BC0400) in B. cereus we concluded that they have D5 and D10 activity. Using different mutants well characterized in our lab we found that phospholipids are obligate intermediates for both desaturases since UFAs did not accumulated in mutants in the synthesis of phospholipids, and that ferredoxin and flavodoxins are part of the electron transport system associated with these desaturases. Previous results show that B. cereus UFAs proportion increase as the growth temperature decrease at 25ºC. This response was suppressed by addition of chloramphenicol or rifampicin for D5-Des while D10 was not affected. Surprisingly for D5-Des the levels of UFAs were increased in presence of both antibiotics. The response to temperature was analyzed with Pdes-lacZ fusions and b-galactosidase activity measurements in order to identify a promoter region involved in expression. The dissection of this molecular mechanism in these bacteria will provide important insights into the basic question on the desaturation reaction.