盐胁迫对于聚球藻PCC 7942大片段DNA删除突变株的生理效应

在对聚球藻PCC 7942开展基因组简化的过程中, 发现一些非必需大片段的删除可导致耐盐胁迫能力降低。突变株?Synpcc7942_0233-0253和?Synpcc7942_2169-2187, 其基因组中分别删除了18和14 kb的区域, 在BG11培养液中的生长与野生型没有显著差异, 但在含有0.4 mol/L NaCl的培养液中的生长相对于野生型被严重抑制。进一步分析发现, 在盐胁迫下2个突变株的光合放氧速率比野生型显著下降, 光系统Ⅰ和Ⅱ电子传递速率均低于野生型, 呼吸耗氧速率与野生型相比却维持在较高水平。这些结果说明, 蓝藻基因组中有些非必需基因实际上对于适应胁迫条件是需要的。

PHYSIOLOGICAL EFFECTS OF SALT STRESS ON LARGE-FRAGMENT DELETION MUTANTS OF SYNECHOCOCCUS ELONGATUS PCC 7942

Cyanobacteria are oxygen-evolving photosynthetic prokaryotes that synthesize organic substances from CO₂ and other inorganic nutrients. As a unicellular cyanobacterium, Synechococcus elongatus PCC 7942 can be cultured in large scale photobioreactors and easily genetically manipulated. Through systematic deletions of non-essential genes or regions, the genome of this cyanobacterium can be trimmed into a more suitable chassis for synthetic biological studies. The non-essential genes usually include those involved in responses to environmental changes or stresses. Even so, during the process of genome simplification, physiological effects of large fragment deletions should be monitored at each step. ?Synpcc7942_0233-0253 and ?Synpcc7942_2169-2187 are two mutants of S. elongatus with an 18 kb or a 14 kb deletion of non-essential genome region, named as Synpcc7942_0233-0253 and Synpcc7942_2169-2187, respectively. PCR examinations indicated that these mutants were completely segregated (no wild type genome copy was found). Comparisons of the two mutants and the wild type under different stressful conditions demonstrated that addition of 0.4 mol/L NaCl significantly inhibited the growth of the two mutants; under normal conditions, however, these 2 mutants showed no or very slight difference from the wild type.Under the salt stress condition, the photosynthetic activities of ?Synpcc7942_0233-0253 and ?Synpcc7942_2169-2187 decreased to 41% and 51% of wild type at 96h, respectively; in contrast, the two mutants showed increased respiratory activities. The salt stress reduced electron transfer reactions (ETR) of photosystems (PS) II in the wild type by 52%, in ?Synpcc7942_0233-0253 by 77% and in ?Synpcc7942_2169-2187 by 82%. At the same time, the ETR of PS I decreased by 32% in the wild type, by 50% and 47% in the two mutants, respectively. We reported two examples of large genomic fragment deletion mutants with greatly reduced stress tolerance, and the findings provided necessary information for the design of chassis genome of the cyanobacterium and the control of conditions for industrialization in the future.