鱼菜共生系统中乳酸菌的筛选及其发酵矿化应用

针对鱼菜共生系统固体废弃物资源化利用效率低的问题，该研究旨在筛选出抗逆性好、矿化功能强的鱼源性乳酸菌，加强鱼粪残饵的发酵矿化性能。试验从鱼菜共生系统中的生物滤料和鱼体中分离乳酸菌，并通过抗逆性及发酵矿化性能检测，筛选出2株具有应用潜力的鱼粪残饵矿化菌株，经鉴定分别为乳酸乳球菌（Lactococcus lactis）L1和糊精乳杆菌（Lactobacillus dextrinicus）L2。耐温性、耐酸碱性和耐盐性检测结果显示，L1表现出较好的抗逆性。在 50 ℃时，L1存活率为96.60%，显著高于L2的存活率80.35%（P<0.05）；在pH值分别为5.0和9.0时，L1的存活率分别为65.43%和71.25%，高于L2的存活率31.10%和52.22%（P<0.05）；当盐浓度为60 g/L时，L1的存活率为37.33%，而L2无法存活。通过比较对照组（CK组，未添加乳酸菌）和乳酸乳球菌组（L组，添加乳酸乳球菌）发酵矿化过程中发酵液水质和矿物元素含量，结果显示 L组的有机物降解及矿化效果更好，除硫（S）元素以外，钾（K）、钙（Ca）、镁（Mg）、铁（Fe）、锰（Mn）和锌（Zn）元素的矿化率均在第3天达到最高（27.59%～94.67%）。综上所述，乳酸乳球菌（Lactococcus lactis）具有较强的抗逆性和显著的发酵矿化效果，且其最佳发酵矿化周期为3 d。该研究可为提高鱼菜共生系统固体废弃物资源化利用效率提供技术支持。

Screening lactic acid bacteria for fermentation and mineralization in aquaponic system

Lactic acid bacteria have been widely used as feed additives in aquaculture to improve the absorption of nutrients, as well as the immunity and growth performance of fish. According to the lactic acid bacteria to decompose organic matter, this study aims to improve the utilization efficiency of solid waste resources with high nutrients in aquaponics systems. Fish-derived bacteria were screened with strong resistance and better mineralization function, in order to enhance the fermentation and mineralization of fish waste. The experiments were conducted to take the biofilter media and fish from the aquaponics system as the source of lactic acid bacteria. A series of tests were then performed on the high-temperature tolerance, acid and alkali tolerance, high salt tolerance, and the mineralization performance of various nutrients in fish waste. Two strains were obtained with mineralization function and application potential, which were identified as Lactococcus lactis L1 and Lactobacillus dextrinicus L2, respectively. A comparison was also made on the growth performance of the strains at 10, 20, 30 and 40 °C. The results revealed that the growth of L1 and L2 was inhibited at 10 and 20 °C, while they proliferated normally at 30 and 40 °C. The survival rate of L1 and L2 after 30 min of heating at 50, 60, and 70 °C was examined to verify the high-temperature tolerance of the strains. It was found that the L1 was achieved the better high-temperature tolerance. The survival rate of L1 was 96.60% at 50 °C, which was significantly higher than that of L2 (80.35%). According to the range of water acidity and alkalinity in the environment of aquaculture, the tolerance of the two strains was examined at pH 5.0-9.0. The results showed that the survival rates of L1 (65.43% and 71.25%) were higher than those of L2 (31.10% and 52.22%) at both pH 5.0 and 9.0 (P<0.05). The tolerance of the strains was examined at 15, 30, and 60 g/L salinity, where the mariculture and salinity were considered after the thickening of mariculture sludge. The survival rate of the strains gradually decreased with the increase of salinity. Once the salt concentration was 60 g/L, the survival rate of L1 was 37.33%, while there was no L2 survival. In terms of tolerance to temperature, acid, and alkali, L1 was selected as the subsequent experimental object for the fish waste fermentation mineralization experiment. The control group (no lactic acid bacteria added) and the L group (with Lactococcus lactis added) were divided to last for seven days. A comparison was made on the contents of nitrogen, phosphorus and various mineral elements in the fermentation broth at days 0, 1, 3, 5 and 7. The results showed that better degradation and mineralization of organic matter were achieved in the L group. The highest concentrations of total ammonia nitrogen (TAN) and total nitrogen (TN) in the fermentation broth of the L group were 192.82 and 342.00 mg/L, respectively, which were much higher than the control group (30.29 and 79.00 mg/L, respectively). Potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and zinc (Zn) in the fermentation broth of the L group were significantly higher than those of the control group, except for sulfur (S) and all reached the highest values (27.59%-94.67%) in the 3d. In conclusion, Lactococcus lactis presented the better resistance to heat, salt, acid, and alkali, indicating better fermentation and mineralization of fish waste. Furthermore, 3 d was the optimal cycle of fermentation and mineralization. The finding can provide a strong reference to apply the lactic acid bacteria to the mineralization of solid wastes, in order to improve the nutrient utilization efficiency in aquaponics systems.