Bacterial and Fungal Microbiota of Guinea Grass Silage Shows Various Levels of Acetic Acid Fermentation

Jianjian Hou,Naoki Nishino

doi:10.3390/fermentation8010010

Abstract

This study aimed to gain insights into the bacterial and fungal microbiota associated with the acetic acid fermentation of tropical grass silage. Direct-cut (DC, 170 g dry matter [DM]/kg) and wilted (WT, 323 g DM/kg) guinea grass were stored in a laboratory silo at moderate (25 °C) and high (40 °C) temperatures. Bacterial and fungal microbiota were assessed at 3 days, 1 month, and 2 months after ensiling. Lactic acid was the primary fermentation product during the initial ensiling period, and a high Lactococcus abundance (19.7–39.7%) was found in DC silage. After two months, the lactic acid content was reduced to a negligible level, and large amounts of acetic acid, butyric acid, and ethanol were found in the DC silage stored at 25 °C. The lactic acid reduction and acetic acid increase were suppressed in the DC silage stored at 40 °C. Increased abundances of Lactobacillus, Clostridium, and Wallemia, as well as decreased abundances of Saitozyma, Papiliotrema, and Sporobolomyces were observed in DC silages from day three to the end of the 2 month period. Wilting suppressed acid production, and lactic and acetic acids were found at similar levels in WT silages, regardless of the temperature and storage period. The abundance of Lactobacillus (1.72–8.64%) was lower in WT than in DC silages. The unclassified Enterobacteriaceae were the most prevalent bacteria in DC (38.1–64.9%) and WT (50.9–76.3%) silages, and their abundance was negatively related to the acetic acid content. Network analysis indicated that Lactobacillus was involved in enhanced acetic acid fermentation in guinea grass silage.

Highlights

Microbiota analysis using DNA information has become more sophisticated and accessible in the past 20 years [1]
Network analysis indicated that Lactobacillus was involved in enhanced acetic acid fermentation in guinea grass silage
Methods for microbiota analysis have progressed, most studies have confirmed the well-established knowledge that the rapid growth of lactic acid bacteria (LAB) after sealing determines the success or failure of silage fermentation

Summary

Introduction

Microbiota analysis using DNA information has become more sophisticated and accessible in the past 20 years [1]. Many studies have been conducted to elucidate the microbiota involved in fermentation and the aerobic deterioration of silage, and attempts to develop a novel microbial inoculant are still in progress. With the improvement of harvesting and packaging machinery, techniques for controlling silage quality have been steadily updated. Methods for microbiota analysis have progressed, most studies have confirmed the well-established knowledge that the rapid growth of lactic acid bacteria (LAB) after sealing determines the success or failure of silage fermentation. The silo-to-silo and year-to-year quality variations remain unsolved, and mold growth during the long-term storage of bale silage is still unavoidable. Lactobacillus buchneri and its related hetero-fermentative LAB species have been the only choice to prevent aerobic deterioration for more than two decades [2]

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Conclusion