耐低营养乳酸菌筛选及对难青贮牧草发酵品质的影响

Screening low-nutrient-tolerant lactic acid bacteria and their effects on the fermentation quality of silages from poor materials

水溶性碳水化合物(WSC)含量低和乳酸菌附着数量少的牧草难以成功青贮,通常添加糖类物质和乳酸菌改善其青贮发酵品质,但成本较高。本研究通过配制不同糖含量(0.002、0.02、0.2、2和20 g·L^(-1))和pH(4.0和4.5)的培养基,筛选耐低营养且耐酸的乳酸菌,添加到不易青贮的柱花草和苏丹草中,研究其对改善发酵品质的效果。结果表明:初筛得到10株较耐低营养的乳酸菌,其中菌株SCLN_(1)和HT_(1)耐低营养和耐酸性均优、菌株LM1为较耐低营养的耐酸菌株。SCLN_(1)经16S rDNA和生理生化特性鉴定后为植物乳杆菌,LM1和HT1为实验室保存菌株,分别为肠膜明串珠菌和鼠李糖乳杆菌。添加到柱花草和苏丹草青贮60 d后,未加菌的发酵品质均较差,pH高于5.0,乳酸含量低于2%DM,氨态氮(NH3-N)含量分别高达30.50%TN和29.01%TN;添加乳酸菌显著改善了2种牧草的青贮发酵品质,尤其是单独添加菌株SCLN_(1),显著降低了柱花草和苏丹草的pH(从5.36和5.19分别降至4.67和4.10)和NH3-N含量(从30.50%TN和29.01%TN分别降至11.24%TN和12.69%TN),增加了乳酸含量(从2.00%DM和1.82%DM分别增加至4.16%DM和8.29%DM);单独添加SCLN_(1)的效果显著优于其他菌株单独添加或与SCLN_(1)混合添加。

Herbage with low water-soluble carbohydrate(WSC)content or low counts of lactic acid bacteria(LAB)is difficult to ensile.Sugars or LAB are usually added to improve the fermentation quality of silage,but the cost is relatively high.In this study,low-nutrient and acid-tolerant LAB were screened by adjusting the glucose content(0.002,0.02,0.2,2 and 20 g·L^(-1))and pH(4.0 and 4.5)of the medium,and inoculating them to stylo(Stylosanthes guianensis)and sudan grass(Sorghum sudanense)with poor ensiling conditions to investigate the silage fermentation quality.Ten low-nutrient-tolerant LAB strains were obtained.Low-nutrient and acid-tolerant strains SCLN_(1)and HT1,and an acid-tolerant strain LM1 with relatively weak tolerance to low nutrient conditions were also obtained.SCLN_(1)was identified Lactobacillus plantarum by 16S rDNA and physiological and biochemical characteristics,and LM1 and HT1 stored in the laboratory were identified as Leuconostoc mesenteroides and Lactobacillus rhamnosus,respectively.After ensiling for 60 days,uninoculated stylo and sudan grass silages had poor fermentation quality,with pH higher than 5.0,lactic acid less than 2%DM,and ammonia nitrogen(NH3-N)reached up to 30.50%TN and 29.01%TN,respectively.Inoculation with LAB significantly improved the fermentation quality of silages of the two tested forage species,especially inoculation with SCLN_(1).For stylo and sudan grass silages,inoculation with SCLN_(1)alone significantly decreased pH values(from 5.36 and 5.19 to 4.67 and 4.10,respectively)and NH_(3)-N content(from 30.50%TN and 29.01%TN to 11.24%TN and 12.69%TN,respectively)and increased lactic acid content(from 2.00%DM and 1.82%DM to 4.16%DM and 8.29%DM,respectively).The effect of inoculation with SCLN_(1)alone was significantly better than that of inoculation with LM_(1)and HT_(1)alone or mixed with SCLN_(1).