Weissella koreensis

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Classification

Weissella koreensis

Kingdom: Bacteria

Division: Firmicutes

Class: Bacilli

Order: Lactobacillales

Family: Leuconostocaceae


Species: Weissella koreensis

NCBI link to find


Description

Kimchi

Weissella koreensis is the predominant lactic acid bacteria (LAB) isolated from kimchi, a traditional Korean fermented-vegetable food [7]. Collins et al. first proposed this species in 1993 based on 16S rRNA gene phylogenetic analysis [6]. Members of the genus Weissella are Gram-positive, facultative anaerobic, non-motile, heterofermentative, non-spore-forming and acid tolerant [3][6]. The cells are either irregular, short rods with rounded to tapered ends or coccoid [6]. As a psychrophilic bacterium, W. koreensis is the dominating species in fermenting kimchi at -1ºC, and it significantly contributes to kimchi’s taste and flavoring [3][7].


Significance

Studies have shown that the LAB isolated during kimchi fermentation exhibit antimicrobial activities by producing compounds such as organic acids, fatty acids and hydrogen peroxide [3]. W. koreensis also shows anti-obesity effects by producing the non-protein amino acid ornithine [7]. W. koreensis contributes to sourdough fermentation to improve the quality of bread by producing D (-)-lactic acid and metabolites from glucose [3] [6]. Acetic acid, being one of the products of fermentation, not only improves the flavor of the sourdough, but also increases the shelf life [3]. It has also been found that W. koreensis inhibits spore germination of the target microorganism during food fermentation [3].

Genome Structure

Strain KCTC 3621 of W.koreensis possesses one chromosome with 1672 coding sequences, 61 tRNA genes and 5 rRNA loci [5]. The chromosome has 1.7Mb and a low GC- content (Guanine-Cytosine content) ratio (35.5%), typical of a low GC Gram-positive phylum Firmicutes [5]. A relatively small percentage of the open reading frames (23.4% ) matches with the potential protein sequence in a public database while 7.7% of the genes are specific in KCTC 3621 but not in other Weissella species’ gene sequences [5]. The genome of strain KACC 15510 of W.koreensis is most closely related to strain KCTC 3621, sharing 98.76% and 99.48% similarity values which further confirms that both strains belong to the same species [5]. Upon studying the genome of strain KCTC 3621, six genes related to ornithine metabolism, five genes related to arginine metabolism and six genes related to antibiotic resistance are found [5].

Lactic Acid Bacteria (LAB) Metabolism

Figure 1. The heterofermentative pathway of lactic acid bacteria. [7]

Heterofermentative LAB use carbohydrates as both a carbon and an energy source. [4][10]. The metabolism of heterofermentative pathway, as compared to homofermentative pathway, results in a diverse set of end products (ethanol, CO2) besides lactic acid [1][8] (Figure 1). As a heterofermentative LAB, W.koreensis uses phosphoketolase pathway when fermenting hexose to lactate, CO2 and ethanol/acetate [1][10]. Glucose is first dehydrogenated to form 6-phosphogluconate, followed by decarboxylation yielding CO2 [1]. Then phosphoketolase cleaves the resulting pentose-5-phosphate into glyceraldehyde phosphate (GAP) and acetyl phosphate [1]. GAP is further metabolized the same way as in the glycolytic pathway, producing lactic acid [1]. Alternatively, if no additional electron acceptor is available (O2), acetyl phosphate is reduced to form ethanol under anaerobic condition [1][8].


Physiological characteristics

Based on morphological, physiological and chemotaxonomic characteristics, strains S-5623 and S-5673 of W. koreensis sp. are considered to represent the novel species of genus Weissella [3][6]. Studies have shown that these two strains are catalase-negative facultative anaerobes [6]. The optimal growth temperature and pH are 25ºC and 6.0 respectively [6], with a sub-zero low-temperature range suggesting a psychrotrophic lifestyle. No growth has been shown in 8 or 10% NaCl [6]. Both strains hydrolyze arginine and form dextran from sucrose [6]. Acid has been produced from L-arabinose, ribose and xylose [6]. Negative results are shown for aesculin hydrolysis and formation of acid from cellobiose, galactose, maltose, melibiose, raffinose, sucrose and trehalose [6]. Both strains produce D (-)-lactic acid and gas from glucose [6].


Anti-obesity Effects

W. koreensis, found in kimchi, is associated with L-Ornithine production from arginine [7]. L-Ornithine is a medicinal, non-protein amino acid which has the potential to combat obesity by promoting hormone release and accelerating basal metabolism rate [7]. W. koreensis strain OK1-6 significantly reduces mRNA expression of C/EBP- α , a potential central regulator for adipocyte development, correlated to lipid accumulation [7]. The decreased expression level of C/EBP- α down-regulates the expression of adipogenic specific genes and results in the reduced accumulation of lipid in cell lines [7].


Ecophysiology

Fig. 2. Change in pH during kimchi fermentation. K1 to K10 are 10 stages during kimchi fermentation.

Lactic acid bacteria (LAB) are characterized by the production of lactic acid as their metabolic end-product from glucose [9]. They are often found in food fermentation environments where there is a rich supply of sugars [1][3]. In addition, LAB, being acid-tolerant and psychrophilic, inhibit the growth of spoilage bacteria and prevent the growth of pathogenic microorganisms during food fermentation when the temperature and pH are low [3][4][9]. Thus, the use of LAB during food fermentation has the potential to reduce the use of chemical preservatives [3][9].


Kimchi fermentation is carried out by dynamic populations of Lactobacillus, Leuconostoc and Weissella species [2]. It has been found that at 10ºC growth environment, Leuconostoc species (Lc.) predominate in the first stage of fermentation (pH >4.6) while W. koreensis predominate after 30 days of fermentation when the environment becomes acidic (pH 4.6) [2] (Figure 3). As a lactic acid bacterium, W.koreensis has been shown to possess the ability to tolerate low pH environments and this allows W.koreensis to outcompete other bacteria in an acidic fermentation environment [2]. In a stressful environment, for an example, -1ºC, and <pH 4.3, W.koreensis is also able to grow and outcompete other species [2].


Fig. 3.  % composition of lactic acid bacterial isolates Lc. citreum and W. koreensis during kimchi fermentation. The kimchi is fermented at 10ºC for 90 days. Data obtained from [2].


Several sugars such as fructose, glucose, and sucrose are present in kimchi [2]. Unlike Leuconostoc species, W.koreensis is incapable of fermenting sucrose though it does use a small amount of sucrose for dextran synthesis [2]. It is likely that W.koreensis ferments kimchi at -1ºC via heterofermentative reaction in which large quantities of acetate is produced from reduction of fructose to mannitol [2].






References

[1] Axelsson, L. 2004. “Lactic acid bacteria: Classification and physiology.” In: Lactic Acid Bacteria, Microbiology and Functonal Aspects., (Eds Salminen, S., Von Wright, A. and Ouwehand A.) Marcel Dekker, Inc., 2004, 1-66.

[2] Cho, J.H., Lee, D.Y., Yang, C.N., Jeon, J.I., Kim, J.H. and Han, H.U. “Microbial population dynamics of kimchi, a fermented cabbage product.” FEMS Microbial Lett, 2006, 257, 262-267.

[3] Choi, H., Kim, Y-W., Hwang, I., Kim, J. and Yoon, S. “Evaluation of Leuconostoc citreum HO12 and Weissella koreensis HO20 isolated from kimchi as a starter culture for whole wheat sourdough.” Food Chemistry, 2012, 134, 2208-2216.

[4] König, H and Fröhlich, J. “Lactic Acid Bacteria.” In: Biology of Microorganisms on Grapes, in Must and in Wine., (König, H., Unden, G. and Fröhlich, J.) Springer Berin Heidelberg, 2009, I, 3-29.

[5] Lee, J.H., Bae, J-W. and Chun, J. “Draft Genome Sequence of Weissella koreensis KCTC 3621 T.” J.Bacteriol, 2012, 194(20), 5711. DOI: 10.1128/JB.01356-12.

[6] Lee, J.S., Lee, K.C., Ahn, J.S., Mheen, T.I., Pyun, Y.R. and Park, Y.H. “ Weissella koreensis sp. nov., isolated from kimchi.” Int. J.Syst. Evol. Microbiol, 2002, 52, 1257– 1261.

[7] Moon, Y.J., Soh, J.R., Yu, J.J., Sohn, H.S., Cha, Y.S. and Oh, S.H. “Intracellular lipid accumulation inhibitory effect of Weissella koreensis OK1-6 isolated from Kimchi on differentiating adipocyte.” J Appl Microbiol, 2012, 113(3), 652-8.

[8] Rὃken, W., Rick, M. and Reinkemeier, M. “Controlled production of acetic acid in wheat sour doughs.” Zeitschrift für Lebensmitteluntersuchung und – Forschung A, 1992,195(3), 259–263.

[9] Scott, R. and Sullivan, W.C. “Ecology of fermented foods.” Human Ecology Review, 2008, 15(1), 25-31.

[10] Zaunmὒller,T., Eichert, M., Richter, H. and Unden, G. “Variations in the energy metabolism of biotechnologically relevant heterofermentative lactic acid bacteria during growth on sugars and organic acids.” Appl Microbiol Biotechnol, 2006, 72, 421-429.



Author

Page authored by Yue Hu, microbiology and immunology student at the University of British Columbia.