Charactrization And Identification Of Lactic Acid Bacteria Isolates And Their Effect On The Frementation Quality Of Elephant And Sweet Sorghum Grass

Elephant grass?Pennistum Purpurem Sch.?and sweet sorghum?sorghum bicolor?are important grasses,which are widely planted in tropic and subtropics regions of the world and commonly used for silage making.Adding lactic acid bacteria?LAB?promote lactic acid fermentation,inhibit butyric fermentation and improve fermentation quality of silage.The growth and activity of LAB are influenced by fermentation days,initial population of LAB,amount of water-soluble carbohydrates and dry matter content[1].The aims of the present study were to isolate LAB,identify them by 16S r DNA sequence and to determine their effect on the fermentation quality of elephant and sweet sorghum grass during ensiling.This work will provide a theoretical basis for developing the LAB resource.There were four parts in the work.1.Isolation and characterization of LAB strains from elephant grassThis experiment aimed to isolate and identify lactic acid bacteria from elephant grass silage and provide the basis for studying the new lactic acid bacteria strains and select potentially excellent strains for silage making.Elephant grass?Pennisetum purpureum?was grown at the experimental field of Nanjing Agricultural University Jiangsu,China?Latitude 32°01₁9? N,Longitude 118°51₀8? E,at Altitude 17 m above sea level?.One hundred and seventy-six strains were isolated and screened from elephant grass silage prepared using a small-scale fermentation system,and seven of these isolates were identified based on morphological,physiological and biochemical characteristics as well as 16S rRNA analysis.The results showed that all seven LAB isolates were classified as homofermentative LAB and were grew at pH 3.5 and all isolates were gram-positive,catalase-negative,and were tolerant to 6.5%NaCl.Strains AZZ1,AZZ2 and AZZ5 were identified as pediococcus acidilactici and AZZ3,AZZ4,AZZ6 and AZZ7 were identified as Lactobacillus plantarum according to the phenotype,16S rRNA,and RecA gene analysis.In conclusions a high rate of isolating lactic acid bacteria was obtained from elephant grass silage.2.Effect of lactic acid bacteria isolates on the fermentation quality of elephant grass during ensilingThe experiment aimed to evaluate the effect of three LAB isolates AZZ1,AZZ4,AZZ7 and a commercial LAB inoculant?CB?on the fermentation quality of elephant grass ensiled at 7,14,30,60 and 90 days.Strains AZZ1,AZZ4,AZZ7 and CB significantly?P<0.05?decreased the pH,dry matter losses,water-soluble carbohydrates?WSC?,acetic acid?AA?,butyric acid?BA?,propionic acid?PA?and ammonia-N?NH3-N?.However,the lactic acid?LA?content significantly?P<0.05?higher compared to the control during ensiling.The strain AZZ4 had the better fermentation quality than AZZ1 and AZZ7 as indicated by the lower pH,AA,BA,PA content and NH3-N?P<0.05?and higher LA content?P<0.05?.In summary,the addition of lactic acid bacteria inoculant improved the fermentation quality of elephant grass.While strain AZZ4 had better fermentation quality compare with other inoculant.3.Effect of lactic acid bacteria isolates on the fermentation quality of sweet sorghum during ensilingThe experiment of isolates AZZ1,AZZ4,AZZ7 and a commercial LAB?CB?on the fermentation quality of sweet sorghum were studied during ensiling.After ensiling days,all LAB isolates had a good lactic acid fermentation indicated by low pH,high LA content.Silage inoculated with CB,AZZ1,AZZ4 and AZZ7 significantly lowered pH and NH3-N content while increased LA content compared with the control during ensiling?P<0.05?.Inoculants were efficient in improving fermentation quality,reducing NH3-N as well as dry matter losses of sweet sorghum silage.In conclusion,the addition of AZZ1,AZZ4 and AZZ7 as inoculants reduced the pH of the sweet sorghum silages and improved silage quality.4.Effect of lactic acid bacteria isolates on fermentation quality and aerobic stabilitry of elephant grass silageThe experiment was conducted to evaluate the effect of isolates(GG13,GG7 and a commercial LAB inoculant?CB?on the fermentation quality and aerobic stability of elephant grass silage ensiled for 3,5,14,30,60,and 90 days.Aerobic stability was determined on day 90 of ensiling.After ensiling GG13,GG7 and CB improved fermentation quality of elephant grass silage by reducing the pH,AA,PA and NH3-N content?P<0.05?and increased LA content?P<0.05?.Control and CB treated silage had higher pH and BA content but both isolates strains decreased pH and BA content?P<0.05?.Silage inoculated with GG7 has the better fermentation quality than GG13 and CB.The aerobic stability of elephant grass silage was decreased with strains treatment compared with the control.In conclusion,these results suggest that,for well-preserved silage,the isolates may be useful as inoculants for silage making,and could play a significant role in developing silage making.