Kimura Yukihiro, Nakata Kazuna, Nojima Shingo, Takenaka Shinji, Madigan Michael T, Wang-Otomo Zheng-Yu
Department of Agrobioscience, Graduate School of Agriculture, Kobe University, Nada, Kobe 657-8501, Japan.
Department of Microbiology, Southern Illinois University, Carbondale, IL 62901, USA.
Microorganisms. 2022 May 2;10(5):959. doi: 10.3390/microorganisms10050959.
() species are the most halophilic and alkaliphilic of all purple bacteria. exhibits the lowest LH1 transition energy among phototrophic organisms and is the only known triply extremophilic anoxygenic phototroph, displaying a thermophilic, halophilic, and alkaliphilic phenotype. Recently, we reported that electrostatic charges are responsible for the unusual spectroscopic properties of the LH1 complex. In the present work, we examined the effects of salt and pH on the spectroscopic properties and thermal stability of LH1-RCs from compared with its mesophilic counterpart, . Experiments in which the photocomplexes were subjected to different levels of salt or variable pH revealed that the thermal stability of LH1-RCs from both species was largely retained in the presence of high salt concentrations and/or at alkaline pH but was markedly reduced by lowering the salt concentration and/or pH. Based on the amino acid sequences of LH1 polypeptides and their composition of acidic/basic residues and the Hofmeister series for cation/anion species, we discuss the importance of electrostatic charge in stabilizing the LH1-RC complex to allow it to perform photosynthesis in its warm, hypersaline, and alkaline habitat.
（某）物种是所有紫色细菌中最嗜盐和嗜碱的。在光合生物中，（该物种）展现出最低的LH1跃迁能量，并且是唯一已知的三重极端厌氧光合自养生物，表现出嗜热、嗜盐和嗜碱的表型。最近，我们报道静电荷是LH1复合体异常光谱特性的原因。在本研究中，我们研究了盐和pH对（该物种）LH1 - RC的光谱特性和热稳定性的影响，并与其嗜温对应物（另一物种）进行了比较。对光复合体施加不同盐浓度或可变pH的实验表明，在高盐浓度和/或碱性pH条件下，两个物种的LH1 - RC的热稳定性基本得以保留，但降低盐浓度和/或pH会使其显著降低。基于LH1多肽的氨基酸序列及其酸性/碱性残基组成以及阳离子/阴离子物种的霍夫迈斯特序列，我们讨论了静电荷在稳定LH1 - RC复合体以使其在温暖、高盐和碱性栖息地进行光合作用中的重要性。
