Prokaryotic Communities in Pit Mud from Different-Aged Cellars Used for the Production of Chinese Strong-Flavored Liquor Yong Tao, Jiabao Li, Junpeng Rui, Zhancheng Xu, Yan Zhou, Xiaohong Hu, Xiang Wang, Menghua Liu, Daping Li and Xiangzhen Li Appl. Environ. Microbiol. 2014, 80(7):2254. DOI: 10.1128/AEM.04070-13. Published Ahead of Print 31 January 2014. Downloaded from Updated information and services can be found at: http://aem.asm.org/content/80/7/2254 These include: http://aem.asm.org/ SUPPLEMENTAL MATERIAL Supplemental material REFERENCES This article cites 38 articles, 12 of which can be accessed free at: http://aem.asm.org/content/80/7/2254#ref-list-1 CONTENT ALERTS Receive: RSS Feeds, eTOCs, free email alerts (when new articles cite this article), more» on March 11, 2014 by guest Information about commercial reprint orders: http://journals.asm.org/site/misc/reprints.xhtml To subscribe to to another ASM Journal go to: http://journals.asm.org/site/subscriptions/ Prokaryotic Communities in Pit Mud from Different-Aged Cellars Used for the Production of Chinese Strong-Flavored Liquor Yong Tao,a Jiabao Li,a Junpeng Rui,a Zhancheng Xu,b Yan Zhou,c Xiaohong Hu,c Xiang Wang,a Menghua Liu,b Daping Li,a Xiangzhen Lia Key Laboratory of Environmental and Applied Microbiology, CAS, Environmental Microbiology Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Sichuan, People’s Republic of Chinaa; Sichuan Jiannanchun Group Co. Ltd., Sichuan, People’s Republic of Chinab; College of Life Science, Sichuan University, Sichuan, People’s Republic of Chinac Chinese strong-flavored liquor (CSFL) accounts for more than 70% of all Chinese liquor production. Microbes in pit mud play key roles in the fermentation cellar for the CSFL production. However, microbial diversity, community structure, and cellar-age- related changes in pit mud are poorly understood. Here, we investigated the prokaryotic community structure and diversity in Downloaded from pit-mud samples with different cellar ages (1, 10, 25, and 50 years) using the pyrosequencing technique. Results indicated that prokaryotic diversity increased with cellar age until the age reached 25 years and that prokaryotic community structure changed significantly between three cellar ages (1, 10, and 25 years). Significant correlations between prokaryotic communities and envi- ؉ ronmental variables (pH, NH4 , lactic acid, butyric acid, and caproic acid) were observed. Overall, our study results suggested that the long-term brewing operation shapes unique prokaryotic community structure and diversity as well as pit-mud chemis- try. We have proposed a three-phase model to characterize the changes of pit-mud prokaryotic communities. (i) Phase I is an initial domestication period. Pit mud is characterized by abundant Lactobacillus and high lactic acid and low pH levels. (ii) Phase II is a transition period. While Lactobacillus abundance decreases dramatically, that of Bacteroidetes and methanogens increases. http://aem.asm.org/ (iii) Phase III is a relative mature period. The prokaryotic community shows the highest diversity and capability to produce more caproic acid as a precursor for synthesis of ethyl caproate, the main flavor component in CSFL. This research provides sci- entific evidence to support the practical experience that old fermentation cellars produce high-quality liquor. hinese strong-flavored liquor (CSFL), also called “Luzhou fla- The pit mud acts as a source of inoculum and a habitat of mi- Cvor liquor,” accounts for more than 70% of Chinese liquor crobes in the brewing fermentation cellar for the CSFL production. production (1). It is produced by the unique and traditional Chi- Previously, the pit-mud microbiota had been studied using cultiva- on March 11, 2014 by guest nese solid-state fermentation technique, which has a history of tion-dependent and -independent approaches. Members of Clostrid- several thousand years. In brief, a cellar is constructed by digging a ium, Bacillus, and Sporolactobacillus genera were isolated and rectangular soil pit in which the entire inner wall is covered with identified from the pit-mud samples (5, 6). Members of six bac- precultured pit mud. The precultured pit mud is usually prepared terial phyla, including Firmicutes, Bacteroidetes, Chloroflexi, Acti- by mixing aged pit mud (as an inoculum), fresh common soil, and nobacteria, unclassified Bacteria, and Proteobacteria, and of one water and incubating the mixture for about a year in an anaerobic archaeal phylum, Euryarchaeota, were identified from the pit- cellar before use. The raw materials for the fermentation, includ- mud samples using denaturing gradient gel electrophoresis ing wheat, sorghum, and corn, are mixed, crushed, and distilled by (DGGE) and clone library analysis of the 16S rRNA gene (7, 8). steaming. The steamed raw material is supplied with 2% to 3% However, big discrepancies in microbial composition existed (wt/wt) Daqu-starter, which mainly includes mold and yeast, and among previous investigations. This may be attributable to differ- placed into the cellar. The cellar is sealed with common mud, and ences in sampling locations in a pit, cellar ages, and laboratory fermentation is allowed to proceed for 60 days. Fermented mate- techniques employed to characterize the community structure. In rial is then taken out of the cellar and distilled to make Chinese addition, most of the previous studies on the pit-mud microbiota liquor. The process described above is periodically repeated after using traditional cultural and molecular methods cannot provide new fermentation materials are supplied. details of the phylogenetic composition and cellar-age-related Microbes in the pit mud produce various flavor components changes of the pit-mud microbial community. Without such in- such as butyric acid, caproic acid, and ethyl caproate. In particu- lar, ethyl caproate is recognized as a key component affecting the CSFL flavor and quality. In general, CSFL quality improves with Received 9 December 2013 Accepted 24 January 2014 increasing cellar age. High-quality liquor is produced only in old Published ahead of print 31 January 2014 cellars, which are maintained at least for 20 years by continuous Editor: J. Björkroth use (2, 3). In particular, some long-aged cellars have been used for Address correspondence to Xiangzhen Li, [email protected]. several hundred years without interruption, and well-known Y.T. and J.L. contributed equally to the article. CSFLs such as Wuliangye, Jiannanchun, and Luzhoulaojiao are Supplemental material for this article may be found at http://dx.doi.org/10.1128 brewed in such long-aged cellars (1, 4). High CSFL quality is at- /AEM.04070-13. tributed to the maturing process of pit mud, which results in a Copyright © 2014, American Society for Microbiology. All Rights Reserved. well-balanced microbial community structure and diversity in the doi:10.1128/AEM.04070-13 pit mud to produce distinctive flavors. 2254 aem.asm.org Applied and Environmental Microbiology p. 2254–2260 April 2014 Volume 80 Number 7 Prokaryotic Community in Pit Mud TABLE 1 Chemical properties in the pit mud Values for cellar of age (yr)a: Variable 1102550 pH 3.57 Ϯ 0.06a 5.00 Ϯ 0.78ac 5.51 Ϯ 0.64bc 5.81 Ϯ 0.33bc ϩ Ϫ1 Ϯ a Ϯ ac Ϯ b Ϯ bc NH4 (g kg ) 1.86 0.06 2.70 0.47 4.21 0.67 3.55 0.68 Moisture (%) 43.3 Ϯ 1.9a 44.5 Ϯ 2.9a 45.1 Ϯ 2.5a 44.1 Ϯ 5.0a Humic matter (%) 30.1 Ϯ 3.6a 26.4 Ϯ 1.2a 24.9 Ϯ 7.3a 21.4 Ϯ 5.6b TN (%) 16.0 Ϯ 0.6a 16.8 Ϯ 2.0a 18.1 Ϯ 2.1a 16.2 Ϯ 1.7a Acetic acid (g kgϪ1) 4.13 Ϯ 0.63a 2.94 Ϯ 0.70a 4.37 Ϯ 0.98a 3.98 Ϯ 0.86a Butyric acid (g kgϪ1) 2.89 Ϯ 0.20a 1.77 Ϯ 0.1b 2.02 Ϯ 0.63b 1.63 Ϯ 0.24b Caproic acid (g kgϪ1) 5.79 Ϯ 0.72a 6.51 Ϯ 3.35a 20.0 Ϯ 8.66b 15.2 Ϯ 7.7b Lactic acid (g kgϪ1) 166.5 Ϯ 12.5a 59.1 Ϯ 21.3b 26.2 Ϯ 10.3b 29.8 Ϯ 4.5b a All data are presented as means Ϯ standard deviations (n ϭ 5). Values with different letters in a row mean significant differences at P Ͻ 0.05 as determined by ANOVA. Downloaded from formation, the specific microbes controlling the CSFL quality can- tional taxonomic units (OTUs) were classified using 97% of 16S rRNA not be identified. gene sequence similarity as a cutoff. Only the OTUs containing at least 5 In this study, we investigated prokaryotic communities in the pit reads were considered to be valid OTUs in this study. Shannon index and mud from different-aged cellars used for CSFL production with the Chao1 estimator values were calculated in RDP at 97% sequence similar- 16S rRNA gene pyrosequencing technique. Pit-mud samples were ity (http://pyro.cme.msu.edu/). The phylogenetic affiliation of each se- collected from a famous CSFL manufacturer located in Sichuan prov- quence was analyzed by RDP Classifier at a confidence level of 80%. The original pyrosequencing data are available at the European Nucleotide ince, China. The aims were to (i) characterize prokaryotic commu- Archive (see below). nity structure and diversity and their cellar-age-related changes in the Statistical analysis. Overall structural changes of prokaryotic com- http://aem.asm.org/ pit mud, (ii) identify important prokaryotic populations in the ma- munities were evaluated by principal coordinates analysis (PCoA) in Fast turing process of pit mud and their possible roles in the CSFL quality, UniFrac (http://bmf.colorado.edu/fastunifrac/). The cluster analysis and (iii) unveil the relationships between chemical properties of pit (CA) was conducted with the unweighted-pair group method using aver- mud and prokaryotic community structure and diversity.