Growth Parameter Components of Adaptive Specificity during Experimental Evolution of the UVR-Inducible Mutator Pseudomonas cichorii 302959

BackgroundMutagenic DNA repair (MDR) transiently increases mutation rate through the activation of low-fidelity repair polymerases in response to specific, DNA-damaging environmental stress conditions such as ultraviolet radiation (UVR) exposure. These repair polymerases also confer UVR tolerance, intimately linking mutability and survival in bacteria that colone habitats subject to regular UVR exposure. Methodology/Principal FindingsHere, we investigate adaptive specificity in experimental lineages of the highly UVR-mutable epiphytic plant pathogen Pseudomonas cichorii 302959. Relative fitness measurements of isolates and population samples from replicate lineages indicated that adaptive improvements emerged early in all lineages of our evolution experiment and specific increases in relative fitness correlated with distinct improvements in doubling and lag times. Adaptive improvements gained under UVR and non-UVR conditions were acquired preferentially, and differentially contributed to relative fitness under varied growth conditions. ConclusionsThese results support our earlier observations that MDR activation may contribute to gains in relative fitness without impeding normal patterns of adaptive specificity in P. cichorii 302959.背景 诱变源性DNA修复（Mutagenic DNA repair, MDR）可通过激活低保真性修复聚合酶，响应紫外线辐射（ultraviolet radiation, UVR）暴露等特定DNA损伤环境胁迫，暂时性提升突变率。此类修复聚合酶同时可赋予UVR耐受性，使得定殖于定期暴露于UVR的生境中的细菌，其突变性与生存性紧密关联。 研究方法与主要结果 本研究针对高UVR诱变的附生植物病原菌菊苣假单胞菌（Pseudomonas cichorii）302959的实验进化谱系开展适应性特异性探究。对重复实验谱系分离得到的菌株及种群样本进行相对适合度（relative fitness）测定，结果显示：本进化实验的所有谱系中，适应性改良均较早出现，且相对适合度的显著提升与倍增时长、延滞时长的明显改善直接相关。在UVR与非UVR条件下获得的适应性改良存在偏好性，且在不同生长条件下对相对适合度的贡献存在差异。 结论 本研究结果佐证了我们此前的观测结论：在菊苣假单胞菌302959中，诱变源性DNA修复（MDR）的激活可在不干扰正常适应性特异性模式的前提下，提升菌株的相对适合度。