The highly conserved ATP-dependent Lon protease plays important roles in diverse biological processes. The lon gene is usually nonessential for viability; however, lon mutants of several bacterial species, although viable, exhibit cellular defects. Here, we show that a lack of Lon protease causes pleiotropic effects in the rice pathogen Burkholderia glumae. The null mutation of lon produced three colony types, big (BLONB), normal (BLONN), and small (BLONS), in Luria-Bertani (LB) medium. Colonies of the BLONB and BLONN types were re-segregated upon subculture, while those of the BLONS type were too small to manipulate. The BLONN type was chosen for further studies, as only this type was fully genetically complemented. BLONN-type cells did not reach the maximum growth capacity, and their population decreased drastically after the stationary phase in LB medium. BLONN-type cells were defective in the biosynthesis of quorum sensing (QS) signals and exhibited reduced oxalate biosynthetic activity, causing environmental alkaline toxicity and population collapse. Addition of excessive N-octanoyl-homoserine lactone (C8-HSL) to BLONN-type cell cultures did not fully restore oxalate biosynthesis, suggesting that the decrease in oxalate biosynthesis in BLONN-type cells was not due to insufficient C8-HSL. Co-expression of lon and tofR in Escherichia coli suggested that Lon negatively affects the TofR level in a C8-HSL-dependent manner. Lon protease interacted with the oxalate biosynthetic enzymes, ObcA and ObcB, indicating potential roles for the oxalate biosynthetic activity. These results suggest that Lon protease influences colony morphology, growth, QS system, and oxalate biosynthesis in B. glumae.

中文翻译：

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Lon 蛋白酶在水稻病原体 Burkholderia glumae 的形态生理特征中的重要作用。

高度保守的 ATP 依赖性 Lon 蛋白酶在多种生物过程中发挥重要作用。lon 基因通常对生存能力不是必需的；然而，几种细菌物种的 lon 突变体虽然可行，但表现出细胞缺陷。在这里，我们表明缺乏 Lon 蛋白酶会导致水稻病原体 Burkholderia glumae 的多效性。lon 的无效突变在 Luria-Bertani (LB) 培养基中产生了三种菌落类型，大 (BLONB)、正常 (BLONN) 和小 (BLONS)。BLONB 和 BLONN 类型的菌落在继代培养时重新分离，而 BLONS 类型的菌落太小而无法操作。选择 BLONN 类型进行进一步研究，因为只有这种类型是完全遗传互补的。BLONN型细胞未达到最大生长能力，在 LB 培养基中达到稳定期后，它们的种群数量急剧减少。BLONN 型细胞在群体感应 (QS) 信号的生物合成方面存在缺陷，并表现出草酸盐生物合成活性降低，导致环境碱性毒性和种群崩溃。向 BLONN 型细胞培养物中添加过量的 N-辛酰基-高丝氨酸内酯 (C8-HSL) 并未完全恢复草酸生物合成，这表明 BLONN 型细胞中草酸生物合成的减少不是由于 C8-HSL 不足所致。lon 和 tofR 在大肠杆菌中的共表达表明 Lon 以 C8-HSL 依赖性方式对 TofR 水平产生负面影响。Lon 蛋白酶与草酸盐生物合成酶 ObcA 和 ObcB 相互作用，表明草酸盐生物合成活性的潜在作用。