Physiological Changes And Comparative Proteomic Analysis Of Bacillus Thuringiensis YBT-1520 Under Heat Stress

Bacillus thuringiensis (Bt) has been widely used for 50 years as a safe biopesticide for controlling agricultural and sanitary insect pests because of its insecticidal crystal proteins (ICPs). The strain used in this study was B. ihuringiensis subsp. kurstaki YBT-1520, which demonstrates high insecticidal activities against lepidopteran larvae. YBT-1520 was originally isolated and characterized in our laboratory. In this study a proteomic approach conbined with physiological investigation was used to describe the proteomic and physiological changes and to reveal the survival strategies of Bt YBT-1520 under a long-term heat stress condition (42℃).The changes of the intracellular proteome under heat stress were as follows:(1) some of the heat shock proteins of class I and II (DnaK, GroEL, GrpE and ClpC) were still induced under long-term heat stress; (2) three non-classical heat shock proteins (BDH1, GuaB and GST) were also induced under long-term heat stress, they could be regarded as the specific factors of long-term heat stress; (3) 83% of the differentially expressed intracellular proteins decreased including toxin proteins, potential toxin proteins, proteases and enzymes involved in the basic metabolic pathways. All these decrease proteins were probably due to the proteolysis process of ClpC and/or the stringent responses triggered by heat stress; (4) about 50% of the decreased proteins were recovered at the late stage of heat stress condition, indicating that the heat stressed cells gained the stresss adaptive ability somehow.Heat stress mainly influenced the characteristics of YBT-1520 on four aspects:(1) the ability of synthesis of ICPs and other potential pathogenic factors were lost or significantly decreased; (2) cell adhesion and motility were also lost; (3) the cells did not sporulate, (4) cells kept accumulating poly-β-hydroxybutyrate (PHB).The survival strategies of YBT-1520 under long-term heat stress were as follows. The first strategy:the induction of non-classical heat shock proteins was a kind of supplementary for the fadeaway of classical heat induced proteins. The second one: metabolic adjustment. Cells down-regulated metabolic enzymes to reduce the oxidative stress or other metabolic burden. This regulation was probably due to the proteolysis process and/or the stringent responses. The third strategy:PHB accumulation. Bacterium adjusted the metabolism of PHB and kept accumulating PHB. These strategies would help cells to gain more tolerance to heat stress.