Abstract

In green photosynthetic bacteria, light is absorbed by bacteriochlorophyll (BChl) c/d/e oligomers, which are located in chlorosomes – unique structures created by Nature to collect the energy of very weak light fluxes. Using coherent femtosecond spectroscopy at cryogenic temperature, we detected and studied low-frequency vibrational motions of BChl c oligomers in chlorosomes of the green bacteria Chloroflexus (Cfx.) aurantiacus. The objects of the study were chlorosomes isolated from the bacterial cultures grown under different light intensity. It was found that the Fourier spectrum of low-frequency coherent oscillations in the Q_y band of BChl c oligomers depends on the light intensity used for the growth of bacteria. It turned out that the number of low-frequency vibrational modes of chlorosomes increases as illumination under which they were cultivated decreases. Also, the frequency range within which these modes are observed expands, and frequencies of the most modes change. Theoretical modeling of the obtained data and analysis of the literature led to conclusion that the structural basis of Cfx. aurantiacus chlorosomes are short linear chains of BChl c combined into more complex structures. Increase in the length of these chains in chlorosomes grown under weaker light leads to the observed changes in the spectrum of vibrations of BChl c oligomers. This increase is an effective mechanism for bacteria adaptation to changing external conditions.

中文翻译：

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光合绿色细菌叶绿素寡聚物的低频振荡

摘要

在绿色光合细菌中，光被细菌叶绿素 (BChl) c / d / e低聚物吸收，这些低聚物位于叶绿体中，这是大自然创造的独特结构，用于收集非常弱的光通量的能量。在低温下使用相干飞秒光谱，我们检测并研究了绿色细菌Chloroflexus  ( Cfx .) aurantiacus叶绿体中 BChl c寡聚物的低频振动运动 。研究对象是从在不同光强度下生长的细菌培养物中分离出的叶绿体。研究发现，BChl  c低聚物 Q _y波段低频相干振荡的傅立叶光谱取决于细菌生长所用的光强度。事实证明，叶绿体的低频振动模式的数量随着培养它们的光照的减少而增加。此外，观察到这些模式的频率范围扩大，并且大多数模式的频率发生变化。对所获得数据的理论建模和文献分析得出的结论是Cfx的结构基础。 aurantiacus叶绿体是 BChl c的短线性链， 组合成更复杂的结构。在弱光下生长的叶绿体中这些链长度的增加导致观察到 BChl c低聚物振动光谱的变化 。这种增加是细菌适应不断变化的外部条件的有效机制。