苏云金芽孢杆菌gerA操纵子在芽孢萌发中的作用

The gerA operon is required for spore germination in Bacillus thuringiensis

芽孢萌发的营养诱导剂通过与特异的萌发受体结合激活下游的萌发过程,从而使芽孢经过一系列的遗传变化及生化反应恢复营养生长。从苏云金芽孢杆菌(Bacillus thuringiensis)中克隆到一个与枯草芽孢杆菌(Bacillus subtilis)gerA操纵子和蜡状芽孢杆菌(Bacillus cereus)gerR操纵子同源的gerA操纵子。苏云金芽孢杆菌gerA操纵子含有3个开放读码框:gerAA、gerAC和gerAB,该操纵子在产孢起始3个小时后开始转录。gerA的破坏阻断了L-丙氨酸诱导的芽孢萌发并且延迟了肌苷诱导的萌发。在L-丙氨酸诱导芽孢萌发的过程中D-环丝氨酸能够提高芽孢的萌发率。

Spore germination of Bacillus could be triggered by germinants like L-alanine which is thought to bind to and stimulate specific receptors. The GerA receptor responds to L-alanine in Bacillus subtilis. A homologous gerA operon of B. subtilis was isolated from Bacillus thuringiensis subsp, kurstaki. RT-PCR showed that the transcription of the gerA operon was switched on 3 hours after the initiation of sporulation and this operon was cotranscribed. Disruption of the gerA operon led to blockage of the L-alanine-initiated germination pathway and showed a delayed inosine-induced germination response. The germination rate of the gerA complementary strain spore deriving from introducing gerA operon into the disruption mutant was even faster than that of the wild type strain spore. This is caused by overdose GerA receptors which could enhance the sensibility of complementary spore to L-alanine. The overdose GerA receptors came from introducing multicopy plasmid- pKSV7 （about five copies） which could increase the amount of GerA receptors. After treatment of D-cycloserine which could inactivate alanine racemase irreversibly, L-alanine-induced spore could germinate faster than untreated spore. The combination of 0.1 mmol/L D-cycloserine and 1 mmol/L L-alanine could trigger spore germination induced by L-alanine effectively.