混合菌群调节果蝇产卵偏嗜性

Mixed bacteria modulate oviposition preference of Drosophila

【目的】利用果蝇产卵偏嗜性作为评价指标,研究影响混合菌群平衡的因素及竞争机制,并揭示混合菌对果蝇后代存活率的影响。【方法】将植物乳杆菌(Lactobacillus plantarum)、大肠杆菌(Escherichia coli)和二者混合菌发酵处理酪蛋白琼脂食物;利用双向选择产卵器检测成年雌性果蝇的产卵偏嗜性;平板计数法检测细菌数量;通过蛹存活率探究两菌互作对果蝇存活率的影响。【结果】在37℃发酵果蝇食物,果蝇喜欢在植物乳杆菌底物上产卵,而厌恶在大肠杆菌底物上产卵,同时对等比例混合菌具有显著的产卵避性,产卵指数为–0.46,说明果蝇产卵偏嗜性可作为一个研究混合菌群平衡的模型。增加混合菌中植物乳杆菌比例可降低果蝇产卵避性,甚至逆转,说明接种比例影响着菌群平衡。涂板计数证实,大肠杆菌数量在培养基中占据优势,是植物乳杆菌的4.43倍,所以引起果蝇产卵避性。当植物乳杆菌与大肠杆菌等比例混合后改变培养温度,25℃对应的产卵指数为0.41,30℃对应的产卵指数为–0.06,35℃对应的产卵指数为–0.45,说明温度影响着菌群平衡。植物乳杆菌代谢物,特别是乳酸可抑制大肠杆菌生长,从而间接地调控果蝇产卵偏嗜性。大肠杆菌占据着优势时,蛹存活率仅为14%,而植物乳杆菌占据着优势时,蛹存活率为91%,说明混合菌生长平衡影响果蝇存活率。【结论】接种比例与温度是影响菌群平衡的关键因素,果蝇根据菌群平衡而调整其产卵行为,以提高后代的存活率。

[Objective] This study aims to investigate how mixed bacteria modulate the oviposition preference of Drosophila through competition and to explore the effect of bacterial balance on Drosophila offspring based on the survival rate and developmental duration. [Methods] Lactobacillus plantarum, Escherichia coli, and the mixture of the two(hereinafter referred to as the mixture) were coated on the casein-sucrose-agar medium(food of Drosophila), respectively. The egg-laying behavior of Drosophila was assayed by a two-choice device. Bacterial count was calculated with the plate method and the effect of the mixture on the survival of Drosophila was evaluated based on the survival rate of pupa. [Results] Drosophila avoided laying eggs on the food that was fermented by E. coli at 37 ℃, while it was attracted to lay eggs on the food fermented by L. plantarum at 37 ℃. The mixture(at the ratio of 1:1) significantly repelled the oviposition of Drosophila, as manifested by the oviposition index(OI) of only-0.46, suggesting Drosophila oviposition preference is an ideal mode for studying the balance of mixed bacteria. Bacterial counting showed that E. coli dominated the medium,with the count 4.43 folds that of L. plantarum, which caused the oviposition avoidance of Drosophila.As expected, increase in the ratio of L. plantarum in the mixed bacteria mitigated or even reversed the oviposition avoidance of Drosophila to fermented diet, indicating that the inoculation ratio of bacteria affected the balance of the flora. With L. plantarum and E. coli mixed at equal ratio, the OI of Drosophila was 0.41 at 25 ℃,-0.06 at 30 ℃, and-0.45 at 35 ℃, suggesting temperature impacted bacterial balance. The metabolites of L. plantarum, particularly lactic acid, inhibited the growth of E. coli, which contributed to the oviposition preference of Drosophila. The survival rate of pupa was 14% when E. coli dominated and 91% when L. plantarum was dominant, indicating that the growth balance of the mixture influenced the survival rate of Drosophila. [Conclusion] Bacterial ratio and culturing temperature determined the final oviposition selection of Drosophila and Drosophila adjusted the oviposition behavior based on bacterial balance to facilitate the survival of offspring.