溶藻细菌L7对水华鱼腥藻氮代谢的影响

【目的】进一步探明藻菌关系,研究溶藻细菌对藻类氮代谢的影响及其作用机制。【方法】将水华鱼腥藻和溶藻细菌L7按两种比例接种入BG11培养液中,在室内进行共培养(藻细胞初始密度为1.21×108cells/L;溶藻细菌L7初始密度分别为1.75×107、1.75×108CFU/mL)。连续7 d测定藻细胞数、异形胞频率和藻细胞内的硝酸还原酶(NR)活性、谷氨酰胺合成酶(GS)活性、谷氨酸合成酶(GOGAT)活性、蛋白质含量、丙二醛(MDA)含量。【结果】低密度溶藻细菌L7能够促进藻生长(第7天藻细胞密度是对照组的1.58倍),增加异形胞频率(第7天高于对照组66.67%);高密度则会抑制藻生长(第7天藻细胞密度相比对照组下降98.84%),降低异形胞频率(第7天为0)。在藻细胞内氮代谢关键酶活性方面,接种后2 5 d,两处理组中藻细胞内NR和GOGAT活性均极显著高于对照组(P<0.01);接种后0 5 d,高密度处理组的GS活性极显著高于对照组(P<0.01),而低密度处理组的则在大部分时间内极显著低于对照组(P<0.01)。在整个实验期内,低密度处理组中藻细胞内蛋白质含量一直极显著高于对照组(P<0.01);而在高密度处理组中,除第5天外,细胞内蛋白质含量则全部极显著低于对照组(P<0.01)。接种后2 4 d,高密度处理组中藻细胞内MDA含量呈现上升趋势,并极显著高于其余两组(P<0.01)。【结论】低密度溶藻细菌L7能够提高水华鱼腥藻对氮源的需求,加速蛋白质合成,促进氮代谢;而高密度溶藻细菌L7会对藻细胞产生过氧化伤害,阻碍蛋白质合成和氮代谢过程。

Effects of the algicidal bacterial strain L7 on nitrogen metabolism of Anabaena flos-aquae

[Objective] The influence mechanism of the algicidal bacterial strain L7 on nitrogen metabolism of Anabaena flos-aquae were investigated to understand the interaction of cyanobacteria-bacteria. [Methods] The algicidal bacterial strain L7 and Anabaena flos-aquae with different ratio were inoculated into BG11 liquid medium. The initial concentration of the algicidal bacterial strain L7 were 1.75×107 and 1.75×108 CFU/mL responding to the same initial concentration of Anabaena flos-aquae (1.21×108 cells/L), respectively. The treatment without the algicidal bacterial strain L7 was set up as the control. The number of cyanobacterial cells, the heterocyst frequency, activities of the nitrate reductase (NR), glutamine synthelase (GS), glutamate synthetase in cyanobacterial cells, and the protein and malondialdehyde (MDA) contents in cyanobacterial cells were measured for 7 days after incubation. [Results] Lower concentration of the algicidal bacterial strain L7 stimulated the growth of the cyanobacteria and increased the heterocyst frequency. On the 7th day, the concentration of cyanobacterial cells and the heterocyst frequency were 1.58 times and 66.67% more than that in the control, respectively. Higher concentration of the algicidal bacterial strain L7 had opposite effects to Anabaena flos-aquae. The cyanobacterial cell concentration was 98.84% less than that in the control and the heterocyst frequency decreased to 0 on the 7th day. As to activities of important enzymes relating to nitrogen metabolism in cyanobacterial cells, activities of NR and GOGAT in two treatments with the algicidal bacterial strain L7 were significantly higher than that in the control between the 2nd and 5th day (P<0.01). In the first 5 days, GS activity was significantly higher than that in the control (P<0.01) in the treatment with higher concentration of the algicidal bacterial strain L7, while lower concentration of the algicidal bacterial strain L7 had opposite effects for most of time. During the entire experiment, the protein content in the treatment with lower concentration of the algicidal bacterial strain L7 was significantly higher than that in the control (P<0.01). However, the protein content in the treatment with higher concentration of the algicidal bacterial strain L7 was always less than that in the control (P<0.01), except on the 5th day. During the period between the 2nd day and the 4th day, the MDA content in the treatment with higher concentration of algicidal bacteria strain L7 exhibited a rising trend and were significantly higher than that in the other treatments (P<0.01). [Conclusion] Lower concentration of the algicidal bacterial strain L7 could stimulate nitrogen metabolism of Anabaena flos-aquae by enhancing its demand for nitrogen and accelerating protein synthesis. Higher concentration of the algicidal bacterial strain L7 could induce membrane lipid peroxidation of Anabaena flos-aquae, thereby inhibiting protein synthesis and nitrogen metabolism.