Kang Yongsung, Hwang Ingyu
Department of Agricultural Biotechnology, Seoul National University, Seoul, Republic of Korea.
PLoS One. 2018 Jan 2;13(1):e0190431. doi: 10.1371/journal.pone.0190431. eCollection 2018.
Bacteria exhibit an optimal growth rate in culture media with sufficient nutrients at an optimal temperature and pH. In addition, the concentration of solutes plays a critical role in bacterial growth and survival. Glutamate is known to be a major anionic solute involved in osmoregulation and the bacterial cell's response to changes in solute concentration. To determine how glutamate uptake is involved in osmoregulation in the rice bacterial pathogen Burkholderia glumae BGR1, we mutated the gltI gene encoding a periplasmic substrate binding protein of a glutamate transport system to abolish glutamate uptake, and monitored the growth of the gltI null mutant in Luria-Bertani medium. We found that the gltI null mutant showed a slower growth rate than the wild-type strain and experienced hyperosmotic stress resulting in water loss from the cytoplasm in stationary phase. When the incubation time was extended, the mutant population collapsed due to the hyperosmotic stress. The gltI null mutant exhibited loss of adaptability under both hypoosmotic and hyperosmotic stresses. The growth rate of the gltI null mutant was restored to the level of wild-type growth by exogenous addition of glycine betaine to the culture medium, indicating that glycine betaine is a compatible solute in B. glumae. These results indicate that glutamate uptake from the environment plays a key role in osmoregulation in B. glumae.
细菌在营养充足、温度和pH适宜的培养基中呈现最佳生长速率。此外，溶质浓度对细菌的生长和存活起着关键作用。谷氨酸是参与渗透调节以及细菌细胞对溶质浓度变化作出反应的主要阴离子溶质。为了确定水稻细菌性病原菌稻瘟病菌BGR1中谷氨酸摄取如何参与渗透调节，我们对编码谷氨酸转运系统周质底物结合蛋白的gltI基因进行突变以消除谷氨酸摄取，并监测gltI缺失突变体在Luria-Bertani培养基中的生长情况。我们发现，gltI缺失突变体的生长速率比野生型菌株慢，并且在稳定期经历高渗胁迫，导致细胞质失水。当延长培养时间时，突变体群体因高渗胁迫而崩溃。gltI缺失突变体在低渗和高渗胁迫下均表现出适应性丧失。通过向培养基中外源添加甘氨酸甜菜碱，gltI缺失突变体的生长速率恢复到野生型生长水平，这表明甘氨酸甜菜碱是稻瘟病菌中的一种相容性溶质。这些结果表明，从环境中摄取谷氨酸在稻瘟病菌的渗透调节中起关键作用。
