Expression Profile and Regulation of Spore and Parasporal Crystal Formation-Associated Genes in Bacillus thuringiensis

Bacillus thuringiensis, a Gram-positive endospore-forming
bacterium, is characterized by the formation of parasporal crystals
consisting of insecticidal crystal proteins (ICPs) during sporulation.
We reveal gene expression profiles and regulatory mechanisms associated
with spore and parasporal crystal formation based on transcriptomics
and proteomics data of B. thuringiensis strain CT-43. During sporulation, five ICP genes encoded by CT-43
were specifically transcribed; moreover, most of the spore structure-,
assembly-, and maturation-associated genes were specifically expressed
or significantly up-regulated, with significant characteristics of
temporal regulation. These findings suggest that it is essential for
the cell to maintain efficient operation of transcriptional and translational
machinery during sporulation. Our results indicate that the RNA polymerase
complex δ and ω subunits, cold shock proteins, sigma factors,
and transcriptional factors as well as the E2 subunit of the pyruvate
dehydrogenase complex could cooperatively participate in transcriptional
regulation via different mechanisms. In particular, differences in
processing and modification of ribosomal proteins, rRNA, and tRNA
combined with derepression of translational inhibition could boost
the rate of ribosome recycling and assembly as well as translation
initiation, elongation, and termination efficiency, thereby compensating
for the reduction in ribosomal levels. The efficient operation of
translational machineries and powerful protein-quality controlling
systems would thus ensure biosyntheses of a large quantity of proteins
with normal biological functions during sporulation.

苏云金芽孢杆菌（Bacillus thuringiensis），一种革兰氏阳性形成芽孢的细菌，其特征在于在芽孢形成过程中，形成由杀虫晶体蛋白（ICPs）组成的孢子外晶体。基于苏云金芽孢杆菌菌株CT-43的转录组学和蛋白质组学数据，我们揭示了与芽孢和孢子外晶体形成相关的基因表达谱和调控机制。在芽孢形成过程中，CT-43编码的五个ICP基因被特异性转录；此外，大部分与芽孢结构、组装和成熟相关的基因均被特异性表达或显著上调，显示出明显的时序调控特征。这些发现表明，细胞在芽孢形成过程中维持转录和翻译机器的高效运作至关重要。我们的结果表明，RNA聚合酶复合体δ和ω亚基、冷休克蛋白、σ因子、转录因子以及丙酮酸脱氢酶复合体的E2亚基可以协同通过不同的机制参与转录调控。特别是，通过不同的机制对核糖体蛋白、rRNA和tRNA的处理与修饰，以及翻译抑制的解除，可以促进核糖体循环和组装速率的提升，以及翻译起始、延伸和终止效率的提高，从而补偿核糖体水平的降低。因此，翻译机器的高效运作和强大的蛋白质质量控制系统确保了在芽孢形成过程中大量正常生物学功能的蛋白质的生物合成。