Screening And Identification Of High-efficiency Acid-producing Bacteria And Its Application In Corn Stalk Silage

In China,the production of crop straws,mainly from corn,wheat,and rice,reached about700 million tons per year.However,their utilization efficiency is extremely low,and most of crop straws were directly burned or discarded in the field,causing not only a huge waste of biomass resources,but also a serious environmental pollution.With the rapid development of animal husbandry industry in China,the shortage of roughage for livestocks becomes more and more prominent.Therefore,the use of crop straws as the roughage is beneficial to alleviating the forage shortage in the animal husbandry industry and provides an effective way for reasonable utilization of resources.Developing silage is a simple and practical way for crop straws as the roughage,which can improve the nutrition and flavor in forage,increase the feed intake of animals,and prolongthe preservation period of forage.Usually,silage is anaerobically fermented by the lactic acid bacteria attached to the surface of plant biomass,but the number of lactic acid bacteria on the surface of biomass is few and a large number of other unbeneficial bacteria affect the quality of silage fermentation,which So,the addition of lactic acid bacterial agent becomes a trend in silage production,for which the strains with high safety and activity are required.In this study,isolation and identification of excellent acid-producing bacteria from the traditional fermented vegetables and the natural fermented silage of Broussonetia papyrifera leaves and oats was conducted.And then,the growth curves,acid production curves,fermentation conditions and safety of these acid-producing bacteria were characterized.Finally,the potential of acid-producing bacteria in the development of corn straw was also evaluated.This study provided excellent bacterial resources as well as a scientific basis for the development of crop straw silage.The main results are as follows:1.A total of 96 clones of acid-producing bacteria were isolated from high-quality traditional fermented vegetables and natural fermented silages.There were 27 strains of Lactobacillus curvatus,6 strains of Lactobacillus plantarum,and 6 strains of Lactobacillus brevis,35 strains of Lactobacillus buchneri,1 strain of Pediococcus pentosaceus,19 strains of Bacillus sp.,1 strain of Staphylococcus cohnii,and 1 strain of Enterococcus sp.identified by 16 S r DNA sequence analysis.Among them,Lactobacillus curvatus G3,Lactobacillus plantarum G17,Lactobacillus brevis Y4,Bacillus YC1-1-4,Lactobacillus buchneri PC-C1,Enterococcus YC2-6,and Pediococcus pentosaceus G18 presented a higher rate of acid production and growth,and a stronger acid tolerance ability.2.The fermentation properties and biological safety of above 7 strains of acid-producing bacteria were analyzed.It was found that maltose was the best carbon source for the growth of bacteria,and yeast powder to be the best nitrogen source,with the best ratio being 1:3.These acid producing bacteria were resistant to tetracycline,kanamycin,streptomy-cin,ampicillin,cefotaxime sodium,and gentamicin,but sensitive to erythromycin and chloram-phenicol.On the other hand,they were antagonistic to pathogens including Staphylococcus aureus,Bacillus cereus,Listeria monocytogenes,Aspergillus niger,Escherichia coli,Salmonella paratyphi B,Serratia marcescens,parahaemolysis Sexual Vibrio,and Micrococcus luteus,but they had no inhibiting effect on Saccharomyces cerevisiae or Bacillus subtilis.3.The effects of acid-producing bacteria on the nutrient quality and fermentation property of corn straw silage were evaluated.Compared to the control without the additives of acid-producing bacteria,the contents of acid detergent fiber,acid detergent lignin,crude fiber,crude ash,and nitrite in the silages fermented with acid-producing bacteria were reduced,but their lactic acid,acetic acid,and crude protein contents were significantly increased.The lowest acid detergent fiber content presented in the silage fermented with L.plantarum or L.plantarum+ L.buchneri,with the lowest acid detergent lignin content for the silage fermented with L.plantarum or L.plantarum + P.pentosaceus,the lowest crude fiber content for the silage fermented with L.plantarum + L.buchneri.Meanwhile,the highest lactic acid content was found in the silage fermented with L.plantarum + L.brevis,with the highest acetic acid content for the silage fermented with L.brevis + P.pentosaceus,the highest crude protein content for the silage fermented with L.plantarum + L.buchneri.However,the nitrite content for all kinds of silages was within the safety range.In addition,adding of heterofermentative lactic acid bacteria(L.buchneri or L.brevis)improved the aerobic stability of silages.The organic acid-producing strains isolated in this study could be used in the production of crop straw silage,which provides an effective way for developing srop straws into animal forages,and as a result is beneficial to reduce the environmental pollution arised from burning crop straw biomass and to relieve the roughage shortage in animal husbandry of our country.