Synergistic Effect in Core Microbiota Associated with Sulfur Metabolism in Spontaneous Chinese Liquor Fermentation
Authors: Liu Jun , Wu Qun , Wang Peng , Lin Jianchun , Huang Ling , Xu Yan 
Published: October 2017

Microbial sulfur metabolism plays crucial roles in various food and alcoholic beverage fermentations. 3-(Methylthio)-1-propanol and dimethyl disulfide are important sulfur compounds in fermented foods and alcoholic beverages. Here, we studied the dynamics of these two compounds during spontaneous Chinese liquor fermentation. The two compounds reached the maximum concentration at day 10 and the maximum production rate at day 3. Metatranscriptomic analysis at days 3 and 10 revealed a total of 354 metabolically active microorganisms.
Saccharomyces
and
Lactobacillus
were identified as core microbiota critical for sulfur compound production based on both the transcript abundances of the principal genes and the distribution frequencies of 31 enzymes involved in sulfur metabolism.
Saccharomyces
transcribed genes encoding 23 enzymes related to the generation of 3-(methylthio)-1-propanol and dimethyl disulfide, and
Lactobacillus
was active in the methyl cycle, which recycles methionine, the precursor of the two sulfur compounds. Furthermore, the sulfur metabolism-related characteristics of two representative species were studied in coculture during a simulated fermentation.
Saccharomyces cerevisiae
JZ109 produced 158.4 μg/liter 3-(methylthio)-1-propanol and 58.5 μg/liter dimethyl disulfide in monoculture, whereas
Lactobacillus buchneri
JZ-JN-2017 could not produce these two compounds in monoculture. Their coculture significantly enhanced the generation of 3-(methylthio)-1-propanol (350.0 μg/liter) and dimethyl disulfide (123.8 μg/liter). In addition, coculture significantly enhanced the gene transcriptions (fold change, 1.5 to ∼55.0) that convert methionine to these two compounds in
S. cerevisiae
and in the methyl cycle of
L. buchneri
. This study reveals a novel synergistic effect between members of the core microbiota in the production of sulfur compounds via methionine recycling in spontaneous Chinese liquor fermentation.

IMPORTANCE
Sulfur compounds play a crucial role in the aroma quality of various fermented foods and alcoholic beverages. However, it is unclear how these compounds are produced by microbes during their spontaneous fermentations. Here, we identified the core microbiota (
Saccharomyces
and
Lactobacillus
) associated with sulfur metabolism by determining both transcript abundance and distribution frequency of each genus in spontaneous Chinese liquor fermentation. This study provides a system-level analysis of sulfur metabolism by the metatranscriptomic analysis and culture-dependent methods. It sheds new light on how the metabolic behavior of the microbiota contributes to the liquor aroma quality. Furthermore, this work reveals a novel synergistic effect between
Saccharomyces
and
Lactobacillus
in the production of sulfur compounds, in which
Lactobacillus
regenerates the precursor methionine for sulfur compound production by
Saccharomyces
. Our findings can contribute to the enhancement of aroma characteristics in Chinese liquor and open new avenues for improving various food and alcoholic beverage fermentation processes.