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To develop a silage fermentation technique to adapt to global climate changes, the microbiome and fermentation dynamics of corn silage inoculated with heat-resistant lactic acid bacteria (LAB) under high-temperature conditions were studied. Corn was ensiled in laboratory silo, with and without two selected strains, Lactobacillus salivarius LS358 and L. rhamnosus LR753, two type strains L. salivarius ATCC 11741T and L. rhamnosus ATCC 7469T. The ensiling temperatures were designed at 30 °C and 45 °C, and the sampling took place after 0, 3, 7, 14, and 60 days of fermentation. The higher pH and dry matter losses were observed in the silages stored at 45 °C compared to those stored at 30 °C. Silages inoculated with strains LS358 and LR753 at 30 °C had a lower ratio of lactic acid/acetic acid. The dominant bacterial genera gradually changed from Pediococcus and Lactobacillus to Lactobacillus in silages during ensiling at 30 °C, while the bacterial community became more complex and fragmented after 7 d of ensiling at 45 °C. The high temperatures significantly led to a transformation of the LAB population from homo-fermentation to hetero-fermentation. This study is the first to describe microbial population dynamics response to high temperature during corn ensiling, and the results indicate that L. rhamnosus 753 shows potential ability to improve silage fermentation in tropics and subtropics.

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Keywords aerobic stability, aflatoxin B1, corn silage, hot and humid, lactic acid bacteria. Correspondence AbstractAim: To effectively make high-quality silage in hot and humid area. Methods and Results: The natural lactic acid bacteria (LAB) strains CZ149, XH358, XH753 and XH761 isolated from corn and Napier grass were screened by the potential of low pH growth and high lactic acid production, and their effect on silage quality, aerobic stability and aflatoxin B1 production of wholecrop corn was also studied in Sichuan, China. Four selected strains were Gram-positive and catalase-negative, rod-shaped strains that are able to grow at pH 3Á5 and at 45°C. Strains CZ149, XH358, XH753 and XH761 were identified as Lactobacillus plantarum, L. salivarius, L. rhamnosus and L. paracasei, respectively. After 60 days of fermentation, all LAB strains showed no significant relationship with the quality of corn silage, whereas the lowest aflatoxin B1 and lactic-to-acetic ratio were detected in strain XH753-treated silage. Strain CZ149-treated silage showed worse aerobic stability and higher aflatoxin B1 concentration than control, whereas strain XH753-treated silage had better aerobic stability and lowest aflatoxin B1 concentration after aerobic exposure in hot and humid condition for 5 days. Conclusions: The three L. plantarum strains used in this study are not suitable as inoculants for local whole-crop corn silage, whereas L. rhamnosus 753 could prolong the aerobic stability and inhibit the accumulation of aflatoxin B1 at hot and humid condition. Significance and Impact of the Study: This study provides new information of LAB inoculants for corn silage in hot and humid areas. Especially, a screened strain of Lactobacillus rhamnosus 753 can be used as a candidate strains to make high-quality silage in tropical and subtropical areas.

To further explore the effects of heterofermentative lactic acid bacteria (LAB) on silage fermentation and aerobic stability, whole-plant corn at around the 1/2 milk-line stage was freshly chopped and ensiled in laboratory silos with deionized water (control), Lactobacillus buchneri (LB), or L. rhamnosus (LR). Each treatment was prepared in triplicate for 3, 14, and 60 d of fermentation, followed by 3 and 7 days of aerobic exposure. The dynamic changes in microbial community were studied by single molecule real-time (SMRT) sequencing. The results showed that the two LAB inoculants altered the microbial communities in different ways. Succession from L. plantarum to L. buchneri and L. rhamnosus was observed in LB- and LR-treated silage, respectively. Both silages improved aerobic stability (82 and 78 h vs. 44 h) by occupying the microbial niche to produce higher levels of acetic acid at terminal fermentation. Because Acetobacter fabarum dominated in the silages after aerobic exposure, beta diversity dramatically decreased. In this study, a. fabarum was reported for the first time in silage and was related to aerobic spoilage. The two heterofermentative LAB produced acetic acid and improved the aerobic stability of the corn silage by occupying the microbial niche at terminal fermentation. Inoculated L. rhamnosus had a greater pH for a longer period of time after opening and less DM loss at day 7.