Department of Physics, University of Pretoria, Lynnwood Road, Pretoria, 0002, South Africa.
Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Lynnwood Road, Pretoria, 0002, South Africa.
Environ Microbiol. 2021 Jul;23(7):3867-3880. doi: 10.1111/1462-2920.15505. Epub 2021 Apr 19.
In hyper-arid soil environments, photosynthetic microorganisms are largely restricted to hypolithic (sub-lithic) habitats: i.e., on the ventral surfaces of translucent pebbles in desert pavements. Here, we combined fluorometric, spectroscopic, biochemical and metagenomic approaches to investigate in situ the light transmission properties of quartz stones in the Namib Desert, and assess the photosynthetic activity of the underlying hypolithic cyanobacterial biofilms. Quartz pebbles greatly reduced the total photon flux to the ventral surface biofilms and filtered out primarily the short wavelength portion of the solar spectrum. Chlorophylls d and f were not detected in biofilm pigment extracts; however, hypolithic cyanobacterial communities showed some evidence of adaptation to sub-lithic conditions, including the prevalence of genes encoding Helical Carotenoid Proteins, which are associated with desiccation stress. Under water-saturated conditions, hypolithic communities showed no evidence of light stress, even when the quartz stones were exposed to full midday sunlight. This initial study creates a foundation for future in-situ and laboratory exploration of various adaptation mechanisms employed by photosynthetic organisms forming hypolithic microbial communities.
在超干旱土壤环境中，光合微生物主要局限于石下（石下）生境：即在沙漠铺砌物中半透明卵石的腹面。在这里，我们结合荧光、光谱、生化和宏基因组学方法，研究纳米比亚沙漠中石英石的原位透光特性，并评估下伏石下蓝藻生物膜的光合作用活性。石英卵石大大降低了腹面生物膜的总光子通量，并主要过滤掉太阳光谱的短波长部分。生物膜色素提取物中未检测到叶绿素 d 和 f；然而，石下蓝藻群落表现出对石下条件的一些适应证据，包括编码螺旋类胡萝卜素蛋白的基因普遍存在，这些基因与干旱胁迫有关。在水饱和条件下，即使石英石暴露在正午的阳光下，石下群落也没有出现光胁迫的迹象。这项初步研究为未来在原位和实验室探索形成石下微生物群落的光合生物所采用的各种适应机制奠定了基础。
