Dynamics of a microbial community during ensiling and upon aerobic exposure in lactic acid bacteria inoculation-treated and untreated barley silages

Highlights

• The stability of silage was improved in LAB-treated barley silage upon aerobic exposure.

• LAB inoculant treatment regulated the effects of aerobic exposure on bacterial community in barley silage upon aerobic exposure.

• The structure of fungal population was significantly modified by LAB inoculant treatment during ensiling.

Abstract

This study investigated the effects of lactic acid bacteria on bacterial and fungal community during the fermentation process and aerobic exposure phase of barley ensiled with preparation of lactic acid bacteria (LAB). The inoculated silages displayed higher contents of lactic acid, acetic acid, and propionic acid as well as a greater number of lactic acid bacteria during ensiling. LAB-treated silage decreased the bacterial diversity during both ensiling and aerobic exposure but increased the fungal diversity during ensiling of barley. LAB-treated silage during ensiling increased the abundance of Lactobacillus but decreased that of Weissella. After aerobic exposure, LAB-treated silage increased the abundance of Lactobacillus but decreased that of Acinetobacter. Acinetobacter, Enterococcus, Providencia, and Empedobacter were the dominant bacteria after aerobic exposure. In conclusion, LAB-treated silage enhanced the number of desirable Lactobacillus and inhibited the growth of undesirable microorganisms, such as Acinetobacter.

Introduction

Barley is one of the main silage materials in China. In the process of feeding, it is easy to cause aerobic spoilage in silage, which not only increases the loss of nutrients, but also reduces the palatability of silage. The growth and reproduction of yeast, mold and some aerobic bacteria, accompanied with the raise of temperature and pH value lead to the decay of silage when the silage is exposed to air (da Silva et al., 2015). These problems might be resolved through the addition of selective additives, which could improve aerobic stability and reduce toxic substances during ensiling. In recent years, silage starter cultures have been widely used to improve the acid formation rate at the onset of ensiling and the stability after aerobic exposure (da Silva et al., 2018, Li et al., 2018, Parvin et al., 2010). The addition of microbial inoculants, such as homofermentative and heterofermentative lactic acid bacteria (LAB), dominates the natural bacteria in the forage and affects the dynamics of the microbial communities during the ensiling (Kung, 1998, Wang et al., 2006). However, the characteristics of fermentative were varied with each individual strain from different silage materials. Inglis et al. (1999) reported the addition of LAB inoculants contained Lactobacillus plantarum and Enterococcus faecium couldnot prevent from deterioration of barley silage in the process of ensiling. While some studies also concentrated on fermentation efficiency, quality, and aerobic stability of the silage by adding LAB inoculants to ensiled plants (Filya et al., 2006, Eikmeyer et al., 2013, Ni et al., 2017a). Several of LAB strains with perfect fermentative parameter were isolated from specific silage materials, such as ryegrass silage, rice straw silage, corn silage (data unpublished), and cultured by our laboratory. Therefore, it is essential to investigate the microbial composition in the process of ensiling and upon aerobic exposure in barley silage treated with LAB inoculants cultured from our laboratory. The quality of the silage depends on the microbial communities and their succession as well as the fermentative metabolites at the onset of ensiling. A better understanding of the microbial communities involved in the ensiling process and upon aerobic exposure could provide additional insight into approaches to improve the conservation of barley silage.

The effects of silage additives on the microbial community composition of silage can be assessed using different techniques, such as culture-based techniques (Ercolini, 2004), real-time PCR (Stevenson et al., 2006), and characterizing the denaturing gradient gel electrophoresis bands. However, all of these approaches underestimate the microbial community composition (Kraut-Cohen et al., 2016). These methods could identify only a few of the predominant operational taxonomic units (OTU) (Temmerman et al., 2003). The next-generation sequencing (NGS) provides a practical method for conducting amplicon sequencing. High throughput sequencing of microbial communities is widely used in various environments (Adams et al., 2009), including silages (Nishino, 2015). By extending the use of NGS technique to ensiling, the effects of the environment and management practices (e.g., crop type, addition of inoculants) on microbial population shifts can be estimated. At present, few reports have applied NGS technique to characterize silage ecology, such as describing the microbial population in alfalfa silage and in an unspecified grass silage (McGarvey et al., 2013, Eikmeyer et al., 2013).

This study aimed to describe the effect of LAB inoculants on fermentation and the bacterial and fungal community dynamics during ensiling and upon aerobic exposure by applying NGS high-throughput sequencing.