饲草附生乳酸菌对碳源的选择性

Silage Carbon Sources Preferred by Epiphytic Lactic Acid Bacteria

【目的】探究饲草源乳酸菌对碳源的选择性,为不同草种筛选适宜的青贮菌种。【方法】选取饲草中分离获得的16株代表性乳酸菌作为研究对象,在MRS液体培养基中以葡萄糖、蔗糖、果糖、木糖、棉籽糖以及5种糖混合为碳源,进行不同菌株发酵培养。每株乳酸菌设3个重复,每个糖处理设空白对照(不接菌)。采用高效液相色谱仪测定各处理发酵24 h后液体培养基中剩余碳源含量和乳酸产量。【结果】(1)蔗糖是大部分菌株发酵首选碳源,在棉籽糖、葡萄糖、果糖和木糖的选择上不同菌株差异较大,发酵乳杆菌(Lactobacillus fermentum,LbFWM)首选棉籽糖和木糖,假肠膜明串珠菌(Leuconostioc pseudomesenteroides,LeP-IR)首选木糖。(2)罗伊氏乳杆菌(Lactobacillus reuteri,LbR-EG)和柠檬明串珠菌(Leuconostoc citreum,LeC-IR)对蔗糖,LbF-WM和LbR-EG对果糖,LbF-WM、LbR-EG和LeP-IR对棉籽糖的利用率均达100%,屎肠球菌(Enterococcus faecium,EF-KG)、短乳杆菌(Lactobacillus brevis,LbB-KG)、戊糖乳杆菌(Lactobacillus pentosus,LbPe-EG)、乳酸乳球菌(Lactococcus lactis,LcL-SC)对葡萄糖的利用率高于其他碳源。(3)灰黄色肠球菌(Enterococcus durans,EG-IR)利用葡萄糖和混合糖,LbPe-EG利用果糖,肠膜明串珠菌(Leuconostoc mesenteroides,LeM-IR)利用棉籽糖和混合糖,LbPe-EG利用蔗糖,LbF-WM利用木糖,格氏乳球菌(Lactococcus garvieae,LcG-IR)利用混合糖发酵乳酸产量最高。(4)耐久肠球菌(Enterococcus durans,ED-IR)利用葡萄糖,植物乳杆菌(Lactobacillus plantarum,LbPl-IR)、LbPe-EG利用果糖,LbPl-IR和LeM-IR利用棉籽糖,LbPe-EG、LbPl-IR和ED-IR利用蔗糖,LeP-IR利用木糖,LcG-IR和EG-IR利用混合糖产乳酸效率较高。LbPl-IR在5种单糖中产酸效率均达80%以上。【结论】不同菌株对同一碳源的利用率、产酸量和产酸效率均不同;同一株菌株对不同碳源的利用率、产酸量和产酸效率也不相同。其中,蔗糖为大部分菌株的首选碳源,蔗糖和葡萄糖的利用率和产乳酸量较高,葡萄糖的产酸效率较高;青贮调制时,可针对饲草中分布乳酸菌种类选择最适碳源。

【Objective】Preferential carbon sources of epiphytic lactic acid bacteria(LAB) were studied in laboratory to aid turning native grasses into silage.【Method】Sixteen representative LAB were isolated from forage and cultured on MRS broth media using glucose,sucrose,fructose,xylose,raffinose,or a mixture of the 5 sugars as carbon source.Three replicates for each LAB strain and a blank control without LAB inoculation for each sugar treatment were included.After incubation for24 h,contents of residual sugars and generated lactic acid in the medium were determined by high-performance liquid chromatography.【Results】(1) Sucrose appeared to be the preferential carbon source by most LAB.Among the other sugars,raffinose and xylose were preferred by Lactobacillus fermentum(Lb F-WM),and xylose by Leuconostoc pseudomesenteroides(Le P-IR).(2) An 100% utilization on sucrose by Lb.reuteri(Lb R-EG) and Leuconostoc citreum(Le C-IR),on fructose by Lb FWM and Lb R-EG,as well as on raffinose by Lb F-WM,Lb R-EG,and Le P-IR was observed.Enterococcus faecium(EF-KG),Lb.brevis(Lb B-KG),Lactobacillus pentosus(Lb Pe-EG),and Lactococcus lactis(Lc L-SC) could more efficiently utilize glucose than the other sugars.(3) The greatest amounts of lactic acid were produced from the fermentation of glucose or the mixed sugars by E.durans(EG-IR),from that of fructose by Lb Pe-EG,from that of raffinose or the sugar mixture by Leuconostoc mesenteroides(Le M-IR),from that of sucrose by Lb Pe-EG,from that of xylose by Lb F-WM,and from that of the mixed sugars by Lactococcus garvieae(Lc G-IR).(4) The lactic acid production was more efficient by E.durans(ED-IR) on glucose,by Lb.plantarum(Lb Pl-IR),or Lb Pe-EG on fructose,by Lb Pl-IR or Le M-IR on raffinose,by Lb Pe-EG,Lb Pl-IR,or ED-IR on sucrose,Le.pseudomesenteroides(Le P-IR) on xylose,and Lc G-IR or EG-IR on mixed sugars.A lactic acid production efficiency greater than 80% was reached by Lb Pl-IR grown on the medium with the mixed sugars.【Conclusion】The sugar utilization and lactic acid production of the LAB fermentations on native grasses varied significantly.Sucrose appeared to be the preferential carbon source by most LAB,sucrose and glucose could obtain the higher utilization rate and lactic acid amount,and glucose could obtain higher lactic acid efficiency.For efficient and effective application of LAB to obtain extended shelf-life silage,it was imperative that careful selection of microbe strains and carbon source be exercised.