| Microbial inoculants are important guarantee to ensure the fermentation quality and safety of ensiled forage crops.However,the mechanism of microbial inoculants regulation on silage fermentation quality is still unclear.Therefore,the objective of this study was to explore the effects of Bacillus and lactic acid bacteria inoculants on the fermentation and micro-ecological process of alfalfa silage and whole-plant corn silage by evaluating the compositions and successions of bacterial community,microbial co-occurrence network and predictive function.The main results of this study are as follows:(1)Effects of antibacterial peptide-producing Bacillus subtilis on the fermentation quality of alfalfa silage and its micro-ecological mechanismsThis study assessed the effects of antibacterial peptide-producing Bacillus subtilis(BS),Lactobacillus buchneri(LB)and their combination(LBBS)on the fermentation characteristics and microbial communities of alfalfa silage during ensiling and aerobic exposure periods.The results showed that inoculation with BS and LB alone or in combination improved the fermentation quality and aerobic stability of alfalfa silage after 60 d of ensiling.The BS-treated silage displayed a higher lactic acid concentration,lower proteolysis and fiber contents than those in the control silage.In addition,both LB and BS treatments increased Lactobacillus and Ascochyta abundances,and decreased Enterococcus and Sporormiacea abundances after 60 d of fermentation.LB and BS inoculation also inhibited the growth of Enterococcus after 3d of aerobic exposure.(2)Effects of antibacterial peptide-producing Bacillus subtilis and Bacillus amyloliquefaciens on the fermentation quality of whole-plant corn silage and its micro-ecological mechanismsThe objective of this study was to investigate effects of Bacillus amyloliquefaciens(BA)and Bacillus subtilis(BS)on the fermentation characteristics,bacterial community and their metabolic pathway of whole-plant corn silage.Results showed that inoculation of BA and BS promoted the lactic acid fermentation of whole-plant corn silage.Application of BA inhibited acetic acid fermentation,whereas BS inoculants inhibited protein degradation.In addition,lower starch contents were observed in BA-and BS-inoculated silages compared with that in control.There was no significant difference in bacterial community among the three groups during ensiling.However,BA and BS inoculations decreased the relative abundances of undesirable bacteria such as Acetobacter and Acinetobacter.Meanwhile,Bacillus was dectected in BA and BS inoculated silage.(3)Effects of different lactic acid bacteria inoculants on the fermentation quality of alfalfa silage and its micro-ecological mechanismsThe objectives of this study were to investigate the adaptation and competition of Lactobacillus plantarum,Pediococcus pentosaceus,and Enterococcus faecalis inoculated in alfalfa silage alone or in combination on the bacterial community,cooccurrence network,and their functional shifts.Before ensiling,alfalfa was inoculated with L.plantarum(Lp),P.pentosaceus(Pp),E.faecalis(Ef),or their combinations(LpPp,LpEf,LpPp Ef).The results showed that Lp,Pp and LpPp inoculated silage with better fermentation quality had simplified bacterial correlation network structures,and lactic acid bacteia was identified as one of the keystone species in Lp,Pp and LpPp inoculated silages.Confusingly,undesirable bacteria were identified as the keystone taxa in Ef,LpEf and LpPp Ef inoculated silages,and poor fermentation quality was observed in these inoculated silages.The relative abundance of P.pentosaceus and E.faecalis increased in Pp and Ef inoculated silage,respectively.While,the growth of P.pentosaceus and E.faecalis were inhibited in LpPp and LpEf inoculated silage,respectively.(4)Effects of lactic acid bacteria inoculants and storage temperatures on the fermentation quality of whole-plant corn silage and its micro-ecological mechanismsThe objective of this study was to investigate effects of Lactobacillus plantarum(LP)and Lactobacillus buchneri(LB)on fermentation process of whole-plant corn silage stored at different temperatures(20℃ or 30℃)based on bacterial community successions,interaction networks and predicted functions.According to bacterial meta-network analysis,species of Lactobacillus and Weissella were sensitive to 30℃,while Leuconostoc species were sensitive to 20℃ in whole-plant corn silage.The storage temperature of 30℃ promoted the lactic acid fermentation,decreased bacterial diversity and network complexity of whole-plant corn silage when compared with 20℃.Additionally,LP inoculation changed the bacterial community successions during the early and middle stages of ensiling,while LB inoculation affected bacterial community successions in the later stage of ensiling.In general,the storage temperature had a greater impact on the fermentation characteristics,bacterial community and predicted function of whole-plant corn silage compared with LAB inoculations.The effect of LB strain on the fermentation processof whole-plant corn silage was more obvious than the LP strain.(5)Effects of lactic acid bacteria inoculants on the fermentation quality of wholeplant corn silage with different dry matter contents and its micro-ecological mechanismsThe objective of this study was to investigate effects of Lactobacillus plantarum(LP)and Lactobacillus buchneri(LB)on fermentation process of whole-plant corn silage with different dry matter content(28%DM and 40%DM)based on bacterial community successions,interaction networks and predicted functions.The results showed that Lactobacillus,Leuconostoc,and Weissella in whole-plant corn silage were more sensitive to 40% DM content,while Leuconostoc and Weissella,and undesirable microorganisms Sphingomonas and Serratia were more sensitive to 28%DM content.Additionally,the LB inoculation completely changed the bacterial community compositions after 60 d of ensiling,and L.buchneri became the only dominant bacterium.In general,the dry matter content of the whole plant corn material had a greater impact on the fermentation characteristics,bacterial community and predicted function of the whole-plant corn silage than lactic acid bacteria inoculants.It is the first time to evaluate effects of Bacillus on the fermentation process of forage silage and its micro-ecological mechanisms based on microbial sequencing technology,which provides an important scientific basis for the creation of novel silage additives.In addition,this study systematically revealed the micro-ecological process and regulation mechanism of lactic acid bacteria additives affecting forage silage fermentation,which provides an important theoretical basis for the regulation of silage fermentation quality. |
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