Fermentation and Microbial Community of Maize Silage Inoculated with Lentilactobacillus buchneri NCIMB 40788 and Contaminated with Bacillus and Clostridium Spore Formers

Abstract

Spore-forming bacteria in silage may reduce dry matter intake or affect dairy product quality when transferred to milk. The present study investigated the effects of three facultative anaerobes (Bacillus cereus, Bacillus subtilis, and Bacillus licheniformis) and two strict anaerobes (Clostridium tyrobutyricum and Clostridium beijerinckii) commonly found in low-quality silage, milk, and cheese. Maize silage was intentionally contaminated with these spore formers in separate mini silos at 1 × 105 CFU spore former per g and treated with commercial silage inoculant Lentilactobacillus buchneri NCIMB 40788 at 4 × 105 CFU per g or left untreated. The microbial and chemical profiles of maize silage, which were determined using Nuclear Magnetic Resonance (NMR), were measured after fermentation for 100 days, and they were also measured for silage exposed to air for 72 h after opening at 100 days. The effect of the inoculant strain L. buchneri NCIMB 40788 on these contaminated silages was investigated to determine if the inoculant could prevent/limit the negative impacts caused by the spore former contaminants. Overall, inoculation improved silage quality and aerobic stability. Acetic acid content was higher in the INOC samples than in the NIS (p < 0.001), while lactic acid content was lower in INOC than in NIS (p < 0.001). Both lactic and acetic acid levels were higher in the silage samples contaminated with B. cereus. Contamination with the spore formers increased the aerobic and anaerobic spore counts of the samples contaminated with B. subtilis and B. licheniformis compared to the control silage after opening. After 3 days of aerobic exposure, the samples contaminated with B. cereus, B. subtilis, and B. licheniformis showed higher aerobic spore counts than the control. The dominant bacterial population was significantly modified by inoculation. Neither inoculation nor contamination types impacted fungal populations upon opening, but a dominance of Wickerhamomyces was observed after aerobic exposure in the B. cereus silages. The γ-aminobutyrate (GABA) content after aerobic exposure was higher than the uncontaminated control for the silage contaminated with B. licheniformis. The samples contaminated with Clostridium species remained largely unchanged compared to the control samples. Physicochemical and bacterial profiles were mainly affected by inoculation, and a limited impact of spore contaminant was noted. Our results show that when L. buchneri inoculation was carried out, higher aerobic and anaerobic spore counts following contamination with bacterial spore formers were mitigated after reaching aerobic stability.