Journal of Microbiology

Journal Articles

Paenibacillus nuruki sp. nov., isolated from Nuruk, a Korean fermentation starter: Soo-Jin Kim , Hayoung Cho , Jae-Hyung Ahn , Hang-Yeon Weon , Jae-Ho Joa , Jeong-Seon Kim , Soon-Wo Kwon; J. Microbiol. 2019;57(10):836-841. Published online June 27, 2019; DOI: https://doi.org/10.1007/s12275-019-9118-3

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Abstract: A Gram-stain-positive, rod-shaped, non-endospore-forming, motile by means of peritrichous flagella, facultatively anaerobic bacterium designated TI45-13arT was isolated from Nuruk, a Korean traditional Makgeolli fermentation starter. It grew at 4–35°C (optimum, 28–30°C), pH 5.0–9.0 (optimum, pH 7.0) and NaCl concentrations up to 5% (w/v). Phylogenetic trees generated using 16S rRNA gene sequences revealed that strain TI45-13arT belonged to the genus Paenibacillus and showed the highest sequence similarities with Paenibacillus kyungheensis DCY88T (98.5%), Paenibacillus hordei RH-N24T (98.4%) and Paenibacillus nicotianae YIM h-19T (98.1%). The major fatty acid was anteiso-C15:0. The DNA G+C content was 39.0 mol%, and MK-7 was the predominant isoprenoid quinone. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, three unidentified glycolipids, and one unidentified aminoglycolipid. The cell-wall peptidoglycan contained meso-diaminopimelic acid. On the basis of polyphasic taxonomy study, it was suggested that strain TI45-13arT represents a novel species within the genus Paenibacillus for which the name Paenibacillus nuruki sp. nov. is proposed. The type strain was TI45-13arT (= KACC 18728T = NBRC 112013T).

A diversity study of Saccharomycopsis fibuligera in rice wine starter nuruk, reveals the evolutionary process associated with its interspecies hybrid: Mohamed El-Agamy Farh , Yunjoo Cho , Jae Yun Lim , Jeong-Ah Seo; J. Microbiol. 2017;55(5):337-343. Published online April 29, 2017; DOI: https://doi.org/10.1007/s12275-017-7115-y

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Abstract: The amylolytic yeast Saccharomycopsis fibuligera is the pre-dominant yeast in the starter product, nuruk, which is utilized for rice wine production in South Korea. Latest molecular studies explore a recently developed interspecific hybridiza-tion among stains of S. fibuligera with a unique genetic fea-ture. However, the origin of the natural hybridization occur-rence is still unclear. Thus, to respectively distinguish paren-tal and hybrid strains, specific primer sets were applied on 141 yeast strains isolated from different nuruk samples fer-mented in different provinces. Sixty-seven strains were de-fined accordingly as parental species with genome A while 8 strains were defined as hybrid strains. Unexpectedly, another parental species with genome B could not be found among the strain pools yet. Furthermore, it was observed that hybrid strains are phenotypically different from A genome strains; asci containing tetrad ascospores were observed in A genome strains more frequent than in hybrid strains. Nevertheless, hybrid strains were slightly more thermotolerant than A ge-nome strains. Interestingly, all hybrid strains were located only in Jeju province. Based on these sets of data, we specu-lated that the unique climate of Jeju province might play an evolutionary role in the interspecific hybridization between A genome strains, as well as the unculturable allopatric B ge-nome strains.

Comprehensive analysis of fungal diversity and enzyme activity in nuruk, a Korean fermenting starter, for acquiring useful fungi: Emily Carroll , Tran Ngoc Trinh , Hokyoung Son , Yin-Won Lee , Jeong-Ah Seo; J. Microbiol. 2017;55(5):357-365. Published online April 29, 2017; DOI: https://doi.org/10.1007/s12275-017-7114-z

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Abstract: Nuruk is a fermenting starter that is involved in the pro-duction of alcoholic beverages, and has been used in South Korea for a very long time. To analyze the fungal diversity, we collected a total of 59 nuruk samples from several com-panies and persons in 2013 to 2014, and obtained 364 iso-lates. All of the single isolated fungi were identified, both morphologically and molecularly, based on the sequences of ribosomal RNA gene [18S, ITS1-5.8S-ITS2, and 26S (D1/D2 region)]. In 46 nuruk samples out of 59 (78%), Saccharo-mycopsis fibuligera, a dimorphic yeast, was most frequently isolated. Among the filamentous fungi, Aspergillus and Lich-theimia were found in more than 50% of the samples with lower colony forming unit (CFU/g of sample) than those of yeasts. The yeasts S. fibuligera and Wickerhamomyces ano-malus were counted with maximum 1.3 – 1.8 × 108 CFU/g. Among Mucorales fungi, Lichtheimia and Mucor were iso-lated in much higher numbers than Rhizopus and Rhizo-mucor. Overall, the home-made nuruks tend to contain more diverse filamentous fungi than the commercial nuruks. To acquire industrially useful filamentous fungi and yeasts, we analyzed the enzyme activities of α-amylase, glucoamylase and acid protease associated with brewing properties for 131 strains. Aspergillus oryzae and S. fibuligera had high α- and glucoamylase activities and most isolates of Lichtheimia ramosa had high acid protease activity. For further applica-tions, 27 fungal strains were chosen based on isolation fre-quencies from nuruk, and the ability to produce useful en-zyme.

Research Support, Non-U.S. Gov'ts

Pyrosequencing reveals bacterial diversity in Korean traditional wheat-based nuruk: Jyotiranjan Bal , Suk-Hyun Yun , Myoung-Suk Choi , Soo-Hwan Yeo , Jung-Mi Kim , Dae-Hyuk Kim; J. Microbiol. 2015;53(12):812-819. Published online December 2, 2015; DOI: https://doi.org/10.1007/s12275-015-5516-3

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Abstract: The emerging global importance of Korea’s alcoholic beverages emphasizes the need for quality enhancement of nuruk, a traditional Korean cereal starter that is used extensively in traditional brewing. Apart from fungi and yeasts, bacteria known to be ubiquitously present are also a part of the nuruk ecosystem and are known to influence fermentation activity by influencing fermentation favorable factors. In the current study, bacterial diversity and temporal variations in the traditional wheat-based nuruk, fermented at two representative temperature conditions for 30 days, along with two commercial wheat-based nuruk samples for comparison analysis were evaluated using libraries of PCR amplicons and 454 pyrosequencing targeting of the hypervariable regions V1 to V3 of the 16S rRNA gene. A total of 90,836 16S reads were analyzed and assigned to a total of 314, 321, and 141 Operational Taxonomic Units (OTUs) for nuruk A, B, and C, respectively. Diversity parameters clearly indicated nuruk B to be more diverse in terms of bacterial composition than nuruk A. Taxonomic assignments indicated that nuruk A was dominated by phylum Cyanobacteria, whereas nuruk B was dominated by phylum Actinobacteria. For both nuruk A and B, members of the phylum Firmicutes mostly converged into the family Bacillaceae; these microorganisms might be present in negligible numbers at the beginning but became significant as the fermentation progressed. The commercial samples were predominated by phylum Firmicutes, which is composed of Lactobacillaceae and Leoconostocaceae. The findings of this study provide new insights into understanding the changes in bacterial community structure during traditional nuruk starter production.

Mycoflora Dynamics Analysis of Korean Traditional Wheat-based Nuruk: Jyotiranjan Bal , Suk-Hyun Yun , Ha-Yeon Song , Soo-Hwan Yeo , Jae Hyun Kim , Jung-Mi Kim , Dae-Hyuk Kim; J. Microbiol. 2014;52(12):1025-1029. Published online November 29, 2014; DOI: https://doi.org/10.1007/s12275-014-4620-0

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Abstract: The growing popularity of traditional Korean alcoholic beverages has led to a demand for quality enhancement of the traditional starter culture nuruk, which consists primarily of wheat. Therefore, this study focused on mycoflora characterization and the temporal variations in traditional wheatbased nuruks fermented at two representative traditional temperature conditions for 30 days. Nuruk A was fermented at a constant temperature of 36°C for 30 days and nuruk B was fermented at a high initial temperature of 45°C for 10 days followed by 35°C for 20 days. The average mycoflora load in the two different nuruk conditions did not vary significantly between the 0 and 30 day cultures, and a maximum load of 8.39 log CFU/g was observed for nuruk A on culture day 3 and 7.87 log CFU/g for nuruk B on culture day 30. Within two samples, pH was negatively correlated with temporal changes in mycoflora load. The pH of nuruk A was significantly lower than that of nuruk B at all of the time points evaluated. Culture- dependent characterization led to the identification of 55 fungal isolates belonging to 9 genera and 15 species, with the most prominent genera comprising Lichtheimia, Penicillium, Trametes, Aspergillus, Rhizomucor, and Mucor. A total of 25 yeast isolates were characterized belonging to 6 genera and 7 species, the most prominent among which were Rhodotorula, Pichia, Debaryomyces, Saccharomycopsis, and Torulospora. Mycofloral community dynamics analysis revealed that both samples A and B varied considerably with respect to the fungal communities over a span of 30 days.

Purification and Characteristics of Glucoamylase in Aspergillus oryzae NR 3-6 Isolated from Traditional Korean Nuruk: Yu, Tae Shick , Kim, Tae Hyoung , Joo, Chong Yoon; J. Microbiol. 1999;37(2):80-85.

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Abstract: The purification system of glucoamylase (glucan 1,4-α-glucosidase, EC 3. 2. 1. 3), some characteristics of the purified enzyme and hydrolysis rate of various raw starch were investigated through several experiments. The enzyme was produced on a solid, uncooked wheat bran medium of Aspergillus oryzae NR 3-6 isolated from traditional Korean Nuruk. The enzyme was homogeneously purified 6.8-fold with an overall yield of 28.3% by the criteria of disc- and SDS-polyacrylamide gel electrophoresis. The molecular weight was estimated to be 48 kDa by SDS-PAGE. The optimum temperature and pH were 55℃ and 4.0, respectively. The enzyme was stable at a pH range of 3.0∼10.0 and below 45℃. Enzyme activity was inhibited about 27% by 1mM Hg^2+. The hydrolysis rate of raw wheat starch was shown to be 17.5-fold faster than the hydrolysis rate of soluble starch. The purified enzyme was identified as glucoamylase because the product of soluble starch by the purified enzyme was mainly glucose by thin layer chromatography.

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