鱼腥蓝细菌PCC 7120游离DnaA的增加降低异形胞频率

INCREASED FREE DNAA DECREASES THE FREQUENCY OF HETEROCYSTS IN ANABAENA SP.PCC 7120

研究在模式生物鱼腥蓝细菌Anabaena sp.PCC 7120中,以DnaA为研究对象,探究蓝细菌细胞周期中复制起始和异形胞分化之间的关系。结果显示:在有氮环境中,DnaA蛋白缺失或过表达并不影响细胞增殖和异形胞的分化。在缺氮环境下,DnaA缺失突变株Malr2009的异形胞分化频率(8.57%)与野生型(8.64%)间无显著差别,且该菌株增殖速率与野生型相比也无显著差异,DnaA蛋白缺失没有影响蓝细菌突变株(Malr2009)的异形胞分化频率和增殖速率。但DnaA蛋白过表达菌株Oalr2009的异形胞分化频率降低了20%,其在第12天A750约为1.2,细胞增殖速率快于野生型(第12天时A750约为0.9),增殖速率提高了30%。综上结果表明在鱼腥蓝细菌PCC 7120中,虽然DnaA不是细胞生长过程所必需的,但在缺氮条件下,游离DnaA增加会抑制异形胞分化频率。

This study investigated the role of DnaA in the relationship between cell cycle and heterocyst differentiation using Anabaena PCC 7120 as the model organism.When providing combined nitrogen,deletion or overexpression of DnaA did not affect cyanobacterial proliferation and heterocyst differentiation.Upon deprivation of combined nitrogen,DnaA deletion(Malr2009)showed no difference in heterocyst frequency(8.57%)compared with the wild type(8.64%)at 24h,and the proliferation rate of Malr2009 was similar to the wild type,DnaA deletion did not affect cyanobacterial frequency of heterocysts or proliferation rate,but the overexpression of DnaA protein(Oalr2009)reduced the frequency of heterocysts by 20% compared with wild type,and increased the cell proliferation rate by 30% with about 1.2 at the 12^(th) day,higher than that of the wild type(about 0.9 at the 12^(th) day).In conclusion,although DnaA is not necessary for the growth of Anabaena sp.PCC 7120 cells,but under deprivation of combined nitrogen,the increased free DnaA inhibited the frequency of heterocysts.