원료 ≫ 감칠맛, MSG

Corynebacteriun : 아미노산의 생산

- 식물 세포벽
- 미생물 세포벽
- 박테리아 세포벽과 생로병사의 비밀

- 세포의 분비, 발효의 산물
- Corynebacteriun : 세포벽과 투과성
- Corynebacteriun : 글루탐산의 생산

Corynebacterium is a genus of bacteria that are gram-positive and aerobic. They are bacilli (rod-shaped), and in some phases of life they are, more particularly, club-shaped, which inspired the genus name (coryneform means "club-shaped").
They are widely distributed in nature in the microbiota of animals (including the human microbiota) and are mostly innocuous.[1] Some are useful in industrial settings such as C. glutamicum.[2] Others can cause human disease, including most notably diphtheria, which is caused by C. diphtheriae. As with various species of a microbiota (including their cousins in the genera Arcanobacterium and Trueperella), they usually are not pathogenic but can occasionally opportunistically capitalize on atypical access to tissues (via wounds) or weakened host defenses.

Industrial uses[edit]
Nonpathogenic species of Corynebacterium are used for very important industrial applications, such as the production of amino acids,[25][26] nucleotides, and other nutritional factors (Martín, 1989); bioconversion of steroids;[27] degradation of hydrocarbons;[28] cheese aging;[29] and production of enzymes.[30] Some species produce metabolites similar to antibiotics: bacteriocins of the corynecin-linocin type,[21][31][32] antitumor agents,[33] etc. One of the most studied species is C. glutamicum, whose name refers to its capacity to produce glutamic acid in aerobic conditions.[34] This is used in the food industry as monosodium glutamate in the production of soy sauce and yogurt.[citation needed]
Species of Corynebacterium have been used in the mass production of various amino acids including glutamic acid, a food additive that is made at a rate of 1.5 million tons/ year. The metabolic pathways of Corynebacterium have been further manipulated to produce lysine and threonine.[citation needed]
L-Lysine production is specific to C. glutamicum in which core metabolic enzymes are manipulated through genetic engineering to drive metabolic flux towards the production of NADPH from the pentose phosphate pathway, and L-4-aspartyl phosphate, the commitment step to the synthesis of L-lysine, lysC, dapA, dapC, and dapF. These enzymes are up-regulated in industry through genetic engineering to ensure adequate amounts of lysine precursors are produced to increase metabolic flux. Unwanted side reactions such as threonine and asparagine production can occur if a buildup of intermediates occurs, so scientists have developed mutant strains of C. glutamicum through PCR engineering and chemical knockouts to ensure production of side-reaction enzymes are limited. Many genetic manipulations conducted in industry are by traditional cross-over methods or inhibition of transcriptional activators.[35]
Expression of functionally active human epidermal growth factor has been brought about in C. glutamicum,[36] thus demonstrating a potential for industrial-scale production of human proteins. Expressed proteins can be targeted for secretion through either the general secretory pathway or the twin-arginine translocation pathway.[37]
Unlike gram-negative bacteria, the gram-positive Corynebacterium species lack lipopolysaccharides that function as antigenic endotoxins in humans.[citation needed]

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Membrane Alteration Is Necessary but Not Sufficient for Effective Glutamate Secretion in Corynebacterium glutamicum
CHRISTIAN HOISCHEN AND REINHARD KRAMER* 1990

In the literature, in general, changes in the lipid membrane of coryneform bacteria were held responsible for effective glutamate secretion in biotin-limited cells (4, 9, 21, 22, 30). Since we showed recently that glutamate efflux cannot be explained by passive diffusion through the altered membrane but on the contrary is mediated by a specific excretion carrier system (14), it was of basic interest to investigate
whether there is, in fact, a close correlation between the lipid composition of the plasma membrane and the activity of glutamate secretion and whether the altered membrane is the ultimate reason for the ability to secrete glutamate. It was important for our studies that we use a new experimental approach by which the same cells could be forced to change directly between producing and nonproducing states, in
contrast to experiments published so far in which two completely different cell populations, i.e., biotin-supplemented nonproducer and biotin-limited producer cells, were always compared.
When we first applied the conventional approach, i.e. analysis of the two different cell populations (Table 1), biotin supplemented and biotin limited, we could confirm the previously published results to a large extent (8, 37, 38, 43, 45). Both the lipid content and the composition of producer cells were altered.
The alternative new experimental approach, which proved to be essential for elucidating the relation of the membrane state and efflux behavior, was a detailed lipid analysis within the first minutes after addition of biotin to glutamate-secreting cells and a direct correlation with amino acid efflux activity. Our experimental results provide strong evidence against a direct relation of the lipid state and efflux activity
(Fig. 2A to E). Biotin addition caused an instant decrease of glutamate secretion, whereas neither the amount of newly synthesized fatty acids nor the phospholipid content changed significantly within the time range in which the full effect on glutamate secretion could already be observed.
Also, the ratio of saturated/unsaturated fatty acids was changed in a much slower time scale. The important energetic parameters, i.e., chemical potential of glutamate and internal glutamate concentration, remained unchanged after biotin addition (not shown). These results demonstrate that effective glutamate efflux is not an obligatory consequence of the altered lipid composition of the membrane.
An alternative hypothesis, however, had to be taken into consideration. Several authors suggested that glutamate secretion may be induced by the presence of a specific phospholipid component (20, 45). Both PIM and the amount of PA and DPG have been made responsible for regulating amino acid efflux (26, 37). Thus, we analyzed the time course of the relative amount of every single phospholipid immediately
after addition of biotin to biotin-limited producer cells. The only significant changes we observed were a relative increase in PA and an undefined component, X. Concomitantly with the transient increase of several of the minor phospholipid components, a transient decrease of the major component, PG, is easy to rationalize. The transient increase of PA was by no means unexpected since PA is the precursor
of the other phopholipids. Thus, the time course of PA concentration in the cells after biotin addition and onset of lipid synthesis closely followed the pattern which would have been expected for a precursor molecule. Also, component X, which is an acidic phospholipid and lacks sugar and nitrogen components, closely followed the "precursorlike" time course of PA. It is thus reasonable to assume that X is
another precursor molecule of the major phospholipid PG, namely, CDP-diacylglycerol or PG-phosphate (2, 12).
Besides the lack of correlation between the decrease in glutamate secretion and significant changes in the lipid composition, we obtained an even stronger argument against a direct functional relation by the experiments described in Fig. 6. If the subtle changes in the lipid content within the first minute(s) after biotin addition were responsible for the instant decrease in glutamate secretion, this effect, hypothetically
due to an altered membrane, should on no account be reverted immediately on blocking fatty acid synthesis again by cerulenin.
The conclusion that the changed lipid composition cannot be the direct trigger for glutamate secretion is further corroborated by a comparison of different bacteria. The phospholipid composition as determined here is more or less in agreement with data published for C. glutamicum (15) and B. ammoniagenes (48). It differs significantly, however, from other coryneform glutamic acid-producing organisms which
show extensive variations in the major components and in the occurrence of nitrogen-containing phospholipids (20, 26, 37).
The arguments put forward so far demonstrate that efflux is not causally related to lipid composition. However, there remained two important questions with respect to the importance
of the lipid state. (i) Is a decrease in lipid content of the
membrane, although not the only factor, in principle a
necessary requirement for glutamate secretion? (ii) Are the
effects of biotin deficiency, on the one hand, and biotin
addition, on the other hand, in fact directly related to the
activity of fatty acid synthesis or possibly (also) to some
other biotin-dependent enzyme systems in the cell?.
By using cerulenin, a specific inhibitor of fatty acid
synthase (Fig. 5 and 6), we could show that cerulenin
directly counteracted the effect of biotin on both fatty acid
synthesis and glutamate secretion. It was possible to switch
from high- to low-level secretion and back again within a
time scale of minutes or less. We conclude that the influence
of biotin is directly related to its effect on fatty acid synthesis,
possibly by a change in metabolic consequences related
to fatty acid synthesis, although we proved (see above) that
the lipid state of the membrane is not the only parameter for
inducing glutamate efflux. Other possible explanations of the
influence of biotin could be ruled out, i.e., an effect via other
biotin-dependent enzymes or carriers (10, 25).
Consequently, it was interesting to test the direct effect of
cerulenin on the activity of glutamate efflux. As could have
been expected from its inhibiting effect on lipid synthesis,
cerulenin in fact led to effective secretion of glutamate.
However, this induction took place only after the lipid
content of the cell has been significantly reduced.
We therefore conclude that, in addition to the obviously
essential prerequisite for effective glutamate secretion, i.e.,
reduced lipid content of the membrane, another regulating
factor(s) is necessary. This was shown by the detailed
analysis of the membrane state and efflux behavior immediately
after biotin addition to producer cells. We have evidence
that there is a superior hierarchy of regulating events
which, in addition to membrane changes, are essential for
effective glutamate secretion; the respective effectors are
parameters of the energy state of the bacterial cell. These
regulation phenomena related to glutamate secretion are
under investigation.

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Mutations of the Corynebacterium glutamicum NCgl1221 Gene, Encoding a Mechanosensitive Channel Homolog, Induce L-Glutamic Acid Production