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

Abstract:

[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.