Frösler Jan, Panitz Corinna, Wingender Jost, Flemming Hans-Curt, Rettberg Petra
1 Biofilm Centre, University of Duisburg-Essen , Essen, Germany .
2 Uniklinik/RWTH Aachen, Institute of Pharmacology and Toxicology , Aachen, Germany .
Astrobiology. 2017 May;17(5):431-447. doi: 10.1089/ast.2015.1431.
Biofilm formation represents a successful survival strategy for bacteria. In biofilms, cells are embedded in a matrix of extracellular polymeric substances (EPS). As they are often more stress-tolerant than single cells, biofilm cells might survive the conditions present in space and on Mars. To investigate this topic, the bacterium Deinococcus geothermalis was chosen as a model organism due to its tolerance toward desiccation and radiation. Biofilms cultivated on membranes and, for comparison, planktonically grown cells deposited on membranes were air-dried and exposed to individual stressors that included prolonged desiccation, extreme temperatures, vacuum, simulated martian atmosphere, and UV irradiation, and they were exposed to combinations of stressors that simulate space (desiccation + vacuum + UV) or martian (desiccation + Mars atmosphere + UV) conditions. The effect of sulfatic Mars regolith simulant on cell viability during stress was investigated separately. The EPS produced by the biofilm cells contained mainly polysaccharides and proteins. To detect viable but nonculturable (VBNC) cells, cultivation-independent viability indicators (membrane integrity, ATP, 16S rRNA) were determined in addition to colony counts. Desiccation for 2 months resulted in a decrease of culturability with minor changes of membrane integrity in biofilm cells and major loss of membrane integrity in planktonic bacteria. Temperatures between -25°C and +60°C, vacuum, and Mars atmosphere affected neither culturability nor membrane integrity in both phenotypes. Monochromatic (254 nm; ≥1 kJ m) and polychromatic (200-400 nm; >5.5 MJ m for planktonic cells and >270 MJ m for biofilms) UV irradiation significantly reduced the culturability of D. geothermalis but did not affect cultivation-independent viability markers, indicating the induction of a VBNC state in UV-irradiated cells. In conclusion, a substantial proportion of the D. geothermalis population remained viable under all stress conditions tested, and in most cases the biofilm form proved advantageous for surviving space and Mars-like conditions. Key Words: Biofilms-Desiccation-UV radiation-Mars-Lithopanspermia. Astrobiology 17, 431-447.
生物膜形成是细菌一种成功的生存策略。在生物膜中，细胞被包裹在胞外聚合物（EPS）基质中。由于生物膜细胞通常比单细胞更耐受压力，它们可能在太空和火星的环境中存活。为了研究这一课题，嗜热栖热菌因其对干燥和辐射的耐受性而被选为模式生物。在膜上培养生物膜，并将悬浮生长并沉积在膜上的细胞作为对照，将它们风干后暴露于包括长时间干燥、极端温度、真空、模拟火星大气和紫外线照射等单个应激源下，还将它们暴露于模拟太空（干燥 + 真空 + 紫外线）或火星（干燥 + 火星大气 + 紫外线）条件的应激源组合下。分别研究了含硫酸盐的火星风化层模拟物在应激过程中对细胞活力的影响。生物膜细胞产生的EPS主要包含多糖和蛋白质。为了检测活的但不可培养（VBNC）细胞，除了菌落计数外，还测定了与培养无关的活力指标（膜完整性、ATP、16S rRNA）。干燥2个月导致生物膜细胞的可培养性下降，膜完整性略有变化，而悬浮细菌的膜完整性则严重丧失。-25°C至+60°C之间的温度、真空和火星大气对两种表型的可培养性和膜完整性均无影响。单色（254 nm；≥1 kJ/m）和多色（200 - 400 nm；悬浮细胞>5.5 MJ/m，生物膜>270 MJ/m）紫外线照射显著降低了嗜热栖热菌的可培养性，但不影响与培养无关的活力标志物，表明紫外线照射的细胞进入了VBNC状态。总之，在所有测试的应激条件下，相当一部分嗜热栖热菌群体仍具有活力，并且在大多数情况下，生物膜形式被证明有利于在类似太空和火星的条件下存活。关键词：生物膜 - 干燥 - 紫外线辐射 - 火星 - 岩石泛种论。天体生物学17，431 - 447。
