Microalgae contributed 60% of the total biomass in the extremely hostile (pH 2 and metal-rich waters) environment of Rio Tinto (which is used as a model for the astrobiology of Mars). These algae are closely related to nonextreme lineages, suggesting that adaptation to Rio Tinto water (RTW) must occur rapidly. Fitness from both the microalga Dictyosphaerium chlorelloides and the cyanobacterium Microcystis aeruginosa was inhibited when they were cultured in RTW. After further incubation for several weeks, D. chlorelloides survived, as a result of the growth of a variant that was resistant to RTW, but RTW-resistant cells did not appear in M. aeruginosa. A Luria-Delbrück fluctuation test revealed that D. chlorelloides RTW-resistant cells arose randomly by rare spontaneous mutations before the RTW exposure (1.38 x 10(-6) mutants per cell division). The mutants with a diminished fitness are maintained in nonextreme waters as the result of a balance between new RTW-resistant cells arising by mutation and RTW-resistant mutants eliminated by natural selection (equilibrium at c. 15 RTW-resistant per 10(7) wild-type cells). Rapid adaptation of eukaryotic algae to RTW could be the result of selection of RTW-resistant mutants occurring spontaneously in nonextreme populations that arrived fortuitously at the river in the past, or in the present continuously.

译文

在力拓 (用作火星天体生物学模型) 的极端敌对 (pH 2和富含金属的水域) 环境中,微藻贡献了总生物量的60%。这些藻类与非极端谱系密切相关,这表明对力拓水 (RTW) 的适应必须迅速发生。在RTW中培养时,微藻绿藻和蓝藻铜绿微囊藻的适应性均受到抑制。进一步孵育数周后,由于对RTW具有抗性的变体的生长,D. chlorelloides得以存活,但铜绿假单胞菌中未出现RTW抗性细胞。Luria-delbr ü ck波动测试表明,在RTW暴露之前,D. chlorelloides RTW抗性细胞是由罕见的自发突变随机产生的 (每个细胞分裂1.38x10(-6) 个突变体)。由于突变产生的新的RTW抗性细胞与自然选择消除的RTW抗性突变体之间的平衡 (每10(7) 野生型细胞在c. 15 RTW抗性时的平衡),适应性减弱的突变体在非极端水域中得以维持。型细胞)。真核藻类对RTW的快速适应可能是选择在过去或现在连续偶然到达河流的非极端种群中自发发生的RTW抗性突变体的结果。

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