The Vibrio fischeri type VI secretion system incurs a fitness cost under host-like conditions.
The Vibrio fischeri type VI secretion system incurs a fitness cost under host-like conditions.
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费氏弧菌 VI 型分泌系统在类似宿主的条件下会产生适应性成本。
DOI：
10.1101/2023.03.07.529561
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Shook,ErikaA
中科院分区：
文献类型：
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作者：
Septer,AleciaN;Sharpe,Garrett;Shook,ErikaA
VI型分泌系统（T6 SS）是由数千个蛋白质亚基组成的细菌间武器，预计需要大量的细胞能量来部署，但很少观察到T6 SS使用的健身成本。在这里，我们确定主机的条件下，T6 SS产生健身成本使用有益的共生体，费氏弧菌，它使用其T6 SS，以消除竞争对手在自然鱿鱼主机。我们假设T6 SS的适应性成本可能取决于细胞的能量状态，并使用理论ATP成本估计来预测T6 SS依赖的适应性成本何时可能明显。理论能量成本估计预测T6 SS在快速生长的群体中使用的相对成本较小（细胞使用的总ATP的0.4-0.45%），而稳定期细胞的相对成本较高（3.1-13.6%）。与这些预测相一致，我们观察到通常用于竞争测定的快速增长的群体没有显著的T6 SS依赖的健身成本。然而，稳定期细胞密度显着较低的野生型菌株相比，不表达T6 SS的调节突变体，这种T6 SS依赖的健身成本是11和23%之间。这种适应性成本可能会影响动物相关细菌中T6 SSs的流行和细菌学。虽然T6 SS可能需要在杀死或被杀死的情况下，一旦竞争对手被淘汰，就不再有选择性的压力来维持武器。我们的研究结果表明，缺乏T6 SS的进化基因型将具有超过其亲本的生长优势，导致非武装人口的最终优势。
The type VI secretion system (T6SS) is an interbacterial weapon composed of thousands of protein subunits and predicted to require significant cellular energy to deploy, yet a fitness cost from T6SS use is rarely observed. Here, we identify host-like conditions where the T6SS incurs a fitness cost using the beneficial symbiont, Vibrio fischeri, which uses its T6SS to eliminate competitors in the natural squid host. We hypothesized that a fitness cost for the T6SS could be dependent on the cellular energetic state and used theoretical ATP cost estimates to predict when a T6SS-dependent fitness cost may be apparent. Theoretical energetic cost estimates predicted a minor relative cost for T6SS use in fast-growing populations (0.4–0.45% of total ATP used cell−1), and a higher relative cost (3.1–13.6%) for stationary phase cells. Consistent with these predictions, we observed no significant T6SS-dependent fitness cost for fast-growing populations typically used for competition assays. However, the stationary phase cell density was significantly lower in the wild-type strain, compared to a regulator mutant that does not express the T6SS, and this T6SS-dependent fitness cost was between 11 and 23%. Such a fitness cost could influence the prevalence and biogeography of T6SSs in animal-associated bacteria. While the T6SS may be required in kill or be killed scenarios, once the competitor is eliminated there is no longer selective pressure to maintain the weapon. Our findings indicate an evolved genotype lacking the T6SS would have a growth advantage over its parent, resulting in the eventual dominance of the unarmed population.