การควบคุมสาหร่ายสีเขียวแกมน้ำเงินสายพันธุ์ LmTK01 ในบ่อกุ้งขาวแวนาไมโดยใช้แบคทีเรียจำเพาะ

Abstract

Blue green algae known as cyanobacteria strain LmTK01 was observed blooming in white-leg shrimp ponds with low shrimp productivity in Songkhla province, Thailand. The objectives of this study were to investigate groups of algae and their physical characteristics and to determine how temperature, pH, and salinity affect the growth of LmTK01. The other objectives included determining the impact of LmTK01 on white-leg shrimp (Litopenaeus vannamei) survival rates and the effectiveness of certain bacteria isolated from shrimp pond water in controlling LmTK01 growth. Bacteria with algicidal activity for controlling the growth of LmTK01 were screened, isolated, and tested in shrimp/algae co-culturing systems to find out the fatal concentration and shrimp survival rate. The results revealed that the typically found in shrimp ponds, blue green algae LmTK01, was round at the cell's end, filamentous without branches, and lacking a mucous sheath. The morphology was like the cyanobacteria genus Limnothrix. There was an aerotrope between the cell and the thylakoid arrangement was a parietal structure. Under controlled temperature (28.00 ± 1.00 °C), the algae exhibited the fastest growth with the maximum optical density (OD, 680 nm.) of 0.611 ± 0.02 and the highest amount of Chl a (97.78 microgram per milliliter). The algae can grow under a relatively wide range of pH and salinity, with optimum growth at pH 8.00 and salinity 15.00 ppt. Co-culturing of these algae at different concentrations (336.17, 703.70 and 1,390.63 microgram Chl a per liter) with white-leg shrimp for 96 hours revealed more than 50% shrimp mortality in all treatments. The algal cells were found in the shrimp's appendages, such as legs, gills, and intestine. This shows that the algae directly interfere with the shrimp's respiratory and digestion system, lower the level of dissolved oxygen, and elevate pH. Fifty-three strains of bacteria from aquaculture pond in Songkhla province were inoculated with LmTK01. It was found that five strains of bacteria were able to inhibit the growth of algae. The bacteria that inhibited algae growth within 7 days were BP5, A2, A5, A7 and HW5, respectively. BP5 showed the highest algicidal activity (99.94%). Endospore formation was also observed in this gram-positive, rod-shaped, creamy, orange-colored colony. The 16s rRNA gene demonstrated that BP5 belonged to the Fictibacillus genus that can inhibit the growth of LmTK01 at an initial concentration of 107 - 108 CFU/mL and without affecting other algae (Chaetoceros sp., Skeletonema sp., Chlorella sp., Scenedesmus sp., and Spirulina sp.). BP5 indirectly affects the growth of LmTK01 (95.20 ± 9.75%), indicated by remaining decomposed algal cells. Additionally, BP5 had no impact on the mortality of shrimp larvae. The effect of BP5 on LmTK01 and white-leg shrimp co-cultivation indicated that shrimp survival (76.67 ± 11.15%) was not different from the control (P > 0.05). In conclusion, the white-leg shrimp culture system provides ideal circumstances for cyanobacteria strain LmTK01 growth, which has a detrimental influence on the shrimp. This negative impact can be mitigated by utilizing bacteria taken from shrimp ponds, genus Fictibacillus, to suppress the growth of cyanobacteria genus Limnothrix strain LmTK01. The isolated bacteria BP5 had the highest algicidal activity and did not affect the survival rate of white shrimp or other microalgae. Therefore, the possibility to control cyanobacteria growth in shrimp culture by specific isolated bacteria. It will be promissing to increase survival and product of shrimp.