Abstract
Knowledge regarding bacterial dynamics during crop ensiling is important for understanding of the fermentation process and may facilitate the production of nutritious and stable silage. The objective of this study was to analyze the bacterial dynamics associated with whole crop wheat silage with and without inoculants. Whole crop wheat was ensiled in laboratory silos, with and without Lactobacillus inoculants (L. plantarum, L. buchneri), for 3 months. Untreated and L. plantarum-treated silages were sampled at several times during ensiling, while L. buchneri-treated silage was sampled only at 3 months. Bacterial composition was studied using next generation sequencing approach. Dominant bacteria, before ensiling, were Pantoea (34.7%), Weissella (28.4%) and Pseudomonas (10.4%), Exiguobacterium (7.8%), and Paenibacillus (3.4%). Exogenous inoculants significantly affected bacterial composition and dynamics during ensiling. At 3 months of ensiling, Lactobacillus dominated the silage bacterial population and reached an abundance of 59.5, 92.5, and 98.2% in untreated, L. plantarum- and L. buchneri-treated silages, respectively. The bacterial diversity of the mature silage was lower in both treated silages compared to untreated silage. Functional profiling of the bacterial communities associated with the wheat ensiling demonstrated that the abundant pathways of membrane transporters, carbohydrate and amino acids metabolisms followed different pattern of relative abundance in untreated and L. plantarum-treated silages. Only three pathways, namely base-excision repair, pyruvate metabolism and transcription machinery, were significantly different between untreated and L. buchneri-treated silages upon maturation. Lactic acid content was higher in L. plantarum-treated silage compared to untreated and L. buchneri-treated silage. Still, the pH of both treated silages was lower in the two Lactobacillus-treated silages compared to untreated silage. Aerobic stability test demonstrated that L. plantarum-, but not L. buchneri-supplement, facilitated silage deterioration. The lower aerobic stability of the L. plantarum-treated silage may be attributed to lower content of acetic acid and other volatile fatty acids which inhibit aerobic yeasts and molds. Indeed, high yeast count was recorded, following exposure to air, only in L. plantarum-treated silage, supporting this notion. Analysis of bacterial community of crop silage can be used for optimization of the ensiling process and the selection of appropriate inoculants for improving aerobic stability.
Highlights
Ensiling of forage crops is widely practiced worldwide in order to ensure continuous feed supply for ruminant livestock
The aerobic stability test indicated that untreated- and Lb-treated silages were more stable than Lptreated silage, as evident by the higher counts of yeast and molds, as well as CO2 produced in the latter case
While recent studies have analyzed the microbiome dynamics during ensiling of several other crops (Keshri et al, 2018; McAllister et al, 2018), the present study is the first to analyze the dynamics of wheat bacterial community in the course of ensiling, as well as during aerobic stability test
Summary
Ensiling of forage crops is widely practiced worldwide in order to ensure continuous feed supply for ruminant livestock. Ensiling fermentation process comprises four main stages: At initial stage, air is still present between the crop particles and the pH value is above 6.0. At this stage a variety of microorganisms are active. At the stage of fermentation, air is depleted through the activity of aerobic microorganisms and LAB become the dominant flora At this stage the pH decreases to a value depending on forage composition and ensiling conditions. Silage remains stable, as long as no air penetrates into it At this stage sometimes, lactic acid is converted gradually to acetic acid by hetero-lactic bacteria, such as Lactobacillus buchneri (Weinberg and Chen, 2013). LAB species commonly used to facilitate the ensiling fermentation belong to the genera Lactobacillus, Lactococcus, Enterococcus, and Pediococcus (Pahlow et al, 2003)
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