Coray Dorien S, Kurenbach Brigitta, Heinemann Jack A
Centre for Integrative Ecology and Centre for Integrated Research in Biosafety, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Microbiology (Reading). 2017 Feb;163(2):122-130. doi: 10.1099/mic.0.000395.
Post-segregational killing (PSK) is a phenotype determined by plasmids using a toxin and an antitoxin gene pair. Loss of the genes depletes the cell's reserve of antitoxin and allows the toxin to act upon the cell. PSK benefits mobile elements when it increases reproductive success relative to other mobile competitors. A side effect of PSK is that plasmids become refractory to displacement from the cell during growth as a monoculture. Most PSK systems use a cytoplasmic toxin, but the external toxins of bacteriocins also have a PSK-like effect. It may be that any toxin and antitoxin gene pair can demonstrate PSK when it is on a plasmid. The secreted ribonuclease barnase and its protein inhibitor barstar have features in common with PSK modules, though their native context is chromosomal. We hypothesized that their recruitment to a plasmid could produce an emergent PSK phenotype. Others had shown that secreted barnase could exert a lethal effect on susceptible bacteria similarly to bacteriocins. However, barnase toxicity did not occur under the conditions tested, suggesting that barnase is toxic to neighbouring cells only under very specific conditions. Bacteriocins are only produced under some conditions, and some conditionality on toxin function or release may be advantageous in general to PSKs with external toxins because it would prevent killing of potential plasmid-naive hosts. Too much conditionality, however, would limit how advantageous the gene pair was to mobile elements, making the genes unlikely to be recruited as a PSK system.
后分离杀伤（PSK）是一种由质粒利用毒素和抗毒素基因对决定的表型。基因的丢失会耗尽细胞内抗毒素的储备，使毒素能够作用于细胞。当PSK相对于其他移动竞争者提高繁殖成功率时，它对移动元件有益。PSK的一个副作用是，在作为单一培养物生长期间，质粒变得难以从细胞中被取代。大多数PSK系统使用细胞质毒素，但细菌素的外毒素也具有类似PSK的作用。可能任何毒素和抗毒素基因对在质粒上时都能表现出PSK。分泌型核糖核酸酶巴纳酶及其蛋白质抑制剂巴尔斯塔与PSK模块有共同特征，尽管它们的天然环境是染色体。我们假设将它们招募到质粒上可能会产生一种新出现的PSK表型。其他人已经表明，分泌的巴纳酶对敏感细菌可产生与细菌素类似的致死作用。然而，在所测试的条件下巴纳酶并未产生毒性，这表明巴纳酶仅在非常特定的条件下对邻近细胞有毒性。细菌素仅在某些条件下产生，毒素功能或释放的某种条件性对于具有外毒素的PSK总体上可能是有利的，因为这将防止杀死潜在的不含质粒的宿主。然而，过多的条件性会限制该基因对移动元件的有利程度，使得这些基因不太可能被招募为PSK系统。
