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Seryoung and Yoneyama, J Biotechnol Biomater 2013, 3:1
http://dx.doi.org/10.4172/2155-952X.1000e118
Biotechnology & Biomaterials
Editorial
Open Access
Amino Acid Exporter: A Tool for the Next-Generation Microbial Fermentation
Kim Seryoung and Hiroshi Yoneyama*
Laboratory of Animal Microbiology, Graduate School of Agricultural Science, Tohoku University, Japan
Amino acids are important biomaterials for the food, chemical,
pharmaceutical, and cosmetic industries. The world market for amino
acids is steadily growing and predicted to go over US$ 10 billion within
a few years [1, 2]. Of the twenty proteogenic amino acids, essential
amino acids, such as lysine, methionine, threonine, and tryptophan
which are not synthesized in animals, constitute a major end-use
market as feed additives with the largest share of the total amino acid
market [3]. Glutamic acid, a sodium salt of which (mono-sodium
glutamate) is extensively used in food as a flavour-enhancer, has the
largest production amounting to approximately two million tons per
year [4].
Amino acid fermentation was triggered in 1957 by the discovery of
the soil bacterium, Corynebacterium glutamicum, which produces large
amounts of glutamic acid in culture medium [5]. Since then, efforts to
produce various amino acids by microbial fermentation resulted in the
development of cost-effective strains with extremely high productivity.
The early strategies for obtaining such a high producer strain were
based on mutagenesis and screening, called metabolic engineering,
which lead to changes in metabolic flow toward a certain amino acid of
interest mainly by deregulation of the amino acid biosynthetic pathway
[6]. As a next step, genetic engineering has been employed recombinant
DNA techniques to improve productivity by cloning a gene that encodes
a rate-limiting enzyme along the biosynthetic pathway of the amino
acid, or by introducing beneficial mutant alleles into the chromosome
of a wild-type background strain [7].
The above mentioned producer strain breeding is fundamentally
based on a wealth of knowledge about biochemistry and genetics of
amino acid biosynthetic pathways including their regulation and of
their catabolism. The process of amino acid fermentation consists of
three parts:
i) uptake of carbon and energy sources from the extracellular
milieus, ii) metabolic changes of the substrates to intermediates and
eventually to products, and iii) efflux of the end-products, amino
acids, into medium. The former two aspects, in particular metabolic
changes, have been the targets for the development of hyper-producing
strains, but the last step has never so far received attention, in part,
due to a lack of knowledge about the amino acids efflux systems.
Significant improvements in microbial amino acid fermentation have
been achieved by the strategies described above, but the productivity
comes near to a limit. Thus, identification and characterization of the
amino acid exporters appear to be of particular importance for further
development of bacterial strains with much higher productivity.
In this context, the molecular mechanism of amino acids export has
long been unknown until the lysE gene was identified to encode L-lysine
exporter, LysE, in C. glutamicum [8]. Interestingly, LysE also exports
L-arginine. After this prominent work, more than ten membrane
proteins have appeared to export amino acids and their analogues in C.
glutamicum and Escherichia coli, substrates of which are L-isoleucine,
L-glutamic acid, L-threonine, L-cysteine, L-leucine, L-valine, and
L-aromatic amino acids. In addition to these exporters, L-alanine
exporter AlaE (formerly YgaW) has recently been identified in E. coli
[9]. The existence of amino acid exporters raises an important question
of why bacterial cells possess these transporters to export L-amino acids
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at the expense of energy, despite the facts that they are anabolic, but not
catabolic, primary metabolites and also are important building blocks of
proteins. The answer to this question will be obtained through in-depth
understanding of the molecular mechanism of substrate excretion by
these exporters and of their regulation. Furthermore, studies on the
novel aspects of amino acid metabolism, that is export, will pave the
way for the next generation amino acid fermentation technology.
References
1. Global Industry Analysts (2012) Amino acids: A global strategic business report.
2. Ziggers D (2011) Report: Global amino acids market to reach $11.6 billion by
2015. All About Feed.
3. Leuchtenberger W, Huthmacher K, Drauz K (2005) Biotechnological production
of amino acids and derivatives: current status and prospects. Appl Microbiol
Biotechnol 69: 1-8.
4. Kojima H, Yasueda H (2011) A new frontier of amino acid fermentation:
metabolic pathway design and advanced fermentation technology. International
Union of Microbiological Societies 2011 Congress (IUMS 2011 Congress),
Sapporo, Japan.
5. Kinoshita S, Udaka S, Shimono M (1957) Studies on the amino acid
fermentation. J Gen Appl Microbiol 3: 193-205.
6. Kramer R (1996) Genetic and physiological approaches for the production of
amino acids. Journal of Biotechnology 45: 1-21.
7. Ikeda M, Ohnishi J, Hayashi M, Mitsuhashi S (2006) A genome-based approach
to create a minimally mutated Corynebacterium glutamicum strain for efficient
L-lysine production. J Ind Microbiol Biotechnol 33: 610-615.
8. Vrljic M, Sahm H, Eggeling L (1996) A new type of transporter with a new type
of a cellular function: L-lysine export from Corynebacterium glutamicum. Mol
Microbiol 22: 815-826.
9. Hori H, Yoneyama H, Tobe R, Ando T, Isogai E, et al. (2011) Inducible L-Alanine
Exporter Encoded by the Novel Gene ygaW (alaE) in Escherichia coli. Appl
Environ Microbiol 77: 4027-4034.
*Corresponding author: Hiroshi Yoneyama, Laboratory of Animal Microbiology,
Graduate School of Agricultural Science, Tohoku University, Japan, Tel: 81-22717-8915; Fax: 81-22-717-8707; E-mail: [email protected]
Received February 27, 2013; Accepted February 28, 2013; Published March 05,
2013
Citation: Seryoung K, Yoneyama H (2013) Amino Acid Exporter: A Tool for
the Next-Generation Microbial Fermentation. J Biotechnol Biomater 3: e118.
doi:10.4172/2155-952X.1000e118
Copyright: © 2013 Seryoung K, et al. This is an open-access article distributed
under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the
original author and source are credited.
Volume 3 • Issue 2 • 1000e118