Centre of Microbial Ecology and Genomics, Department of Genetics, University of Pretoria, Pretoria, South Africa.
Environ Microbiol. 2017 Sep;19(9):3755-3767. doi: 10.1111/1462-2920.13877. Epub 2017 Aug 24.
Microorganisms able to synthesize rhodopsins have the capacity to translocate ions through their membranes, using solar energy to generate a proton motive force. Rhodopsins are the most abundant phototrophic proteins in oceanic surface waters and are key constituents in marine bacterial ecology. However, it remains unclear how rhodopsins are used in most microorganisms. Despite their abundance in marine and fresh-water systems, the presence of functional rhodopsin systems in edaphic habitats has never been reported. Here, we show the presence of several new putative H , Na and Cl pumping rhodopsins identified by metagenomic analysis of Antarctic desert hypolithic communities. Reconstruction of two Proteobacteria genomes harboring xanthorhodopsin-like proteins and one Bacteroidetes genome with a Na-pumping-like rhodopsin indicated that these bacteria were aerobic heterotrophs possessing the apparent capacity for the functional expression of rhodopsins. The existence of these protein systems in hypolithic bacteria expands the known role of rhodopsins to include terrestrial environments and suggests a possible predominant function as heterotrophic energy supply proteins, a feasible microbial adaptation to the harsh conditions prevalent in Antarctic edaphic systems.
能够合成视紫红质的微生物有能力通过它们的膜转运离子，利用太阳能产生质子动力。视紫红质是海洋表面水中最丰富的光养蛋白，也是海洋细菌生态学的关键组成部分。然而，大多数微生物如何使用视紫红质仍然不清楚。尽管它们在海洋和淡水系统中大量存在，但在土壤生境中从未报道过功能性视紫红质系统的存在。在这里，我们通过对南极荒漠隐生群落的宏基因组分析，展示了几种新的推定的 H、Na 和 Cl 泵视紫红质的存在。对含有类菌视紫红质蛋白的两种变形菌基因组和一种具有 Na 泵类似视紫红质的拟杆菌基因组的重建表明，这些细菌是好氧异养菌，具有功能性视紫红质表达的明显能力。这些蛋白系统在隐生细菌中的存在将视紫红质的已知作用扩展到包括陆地环境，并表明其可能主要作为异养能源供应蛋白发挥作用，这是一种可行的微生物适应南极土壤系统普遍存在的恶劣条件的方式。
