Abstract
A potent algicidal bacterium isolated from Lake Taihu, Chryseobacterium sp. strain GLY-1106, produces two algicidal compounds: 1106-A (cyclo(4-OH-Pro-Leu)) and 1106-B (cyclo(Pro-Leu)). Both diketopiperazines showed strong algicidal activities against Microcystis aeruginosa, the dominant bloom-forming cyanobacterium in Lake Taihu. Interestingly, these two algicidal compounds functioned synergistically. Compared with individual treatment, combined treatment with cyclo(4-OH-Pro-Leu) and cyclo(Pro-Leu) significantly enhanced algicidal activity, accelerated the increase in intracellular reactive oxygen species (ROS) levels in M. aeruginosa, and further decreased the activities of antioxidases, effective quantum yield and maximal electron transport rate of M. aeruginosa. The results also showed that the algicidal characteristics of cyclo(4-OH-Pro-Leu) are distinct from those of cyclo(Pro-Leu). Cyclo(4-OH-Pro-Leu) mainly interrupted the flux of electron transport in the cyanobacterial photosynthetic system, whereas cyclo(Pro-Leu) mainly inhibited the activity of cyanobacterial intracellular antioxidases. A possible algicidal mechanism for the synergism between cyclo(4-OH-Pro-Leu) and cyclo(Pro-Leu) is proposed, which is in accordance with their distinct algicidal characteristics in individual and combined treatment. These findings suggest that synergism between algicidal compounds might be used as an effective strategy for the future control of Microcystis blooms.
Highlights
Has been challenged due to the costs and secondary pollution[8], biomanipulation technologies have received particular attention because of their potential efficacy and eco-friendliness[8,9]
Five algicidal bacterial strains were isolated from Lake Taihu, and four algicidal substances were separated and identified from the algicidal bacteria: pigment[14], diketopiperazines (cyclo(Pro-Gly) and cyclo(Pro-Val))[16] and hydroquinone[17]
The strain GLY-1106, which had the strongest algicidal activity (A = 98.9%, t = 6 days), was selected for further in-depth investigation. This strain formed shiny, compact yellow colonies with entire edges, and the morphological examination via transmission electron microscopy revealed that strain GLY-1106 was a rod-shaped (0.5 to 1.0 by 3.0 to 4.0 μ m) bacterium
Summary
Has been challenged due to the costs and secondary pollution[8], biomanipulation technologies have received particular attention because of their potential efficacy and eco-friendliness[8,9]. Many algicidal bacteria have been isolated[9,12,13,14], and some of the corresponding algicidal substances have been purified and identified, including pigments[14,15], diketopiperazines[16,17], proteins[18,19], and other complex compounds[9,20]. Five algicidal bacterial strains were isolated from Lake Taihu, and four algicidal substances were separated and identified from the algicidal bacteria: pigment (isatin)[14], diketopiperazines (cyclo(Pro-Gly) and cyclo(Pro-Val))[16] and hydroquinone[17]. Strain GLY-1106, was isolated from Lake Taihu, which produces two algicidal compounds. The combination of these two algicidal substances showed an enhanced algicidal effect, indicating that synergism existed between the two compounds. This study focused on the possible mechanism involved in the observed algicidal synergism of these two algicidal compounds
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