Although L-serine proceeds in just three steps from the glycolytic intermediate 3-phosphoglycerate, and as much as 8% of the carbon assimilated from glucose is directed via L-serine formation, previous attempts to obtain a strain producing L-serine from glucose have not been successful. We functionally identified the genes serC and serB from Corynebacterium glutamicum, coding for phosphoserine aminotransferase and phosphoserine phosphatase, respectively. The overexpression of these genes, together with the third biosynthetic serA gene, serA ⌬197 , encoding an L-serine-insensitive 3-phosphoglycerate dehydrogenase, yielded only traces of L-serine, as did the overexpression of these genes in a strain with the L-serine dehydratase gene sdaA deleted. However, reduced expression of the serine hydroxymethyltransferase gene glyA, in combination with the overexpression of serA ⌬197 , serC, and serB, resulted in a transient accumulation of up to 16 mM L-serine in the culture medium. When sdaA was also deleted, the resulting strain, C. glutamicum ⌬sdaA::pK18mobglyA (pEC-T18mob2serA ⌬197 CB), accumulated up to 86 mM L-serine with a maximal specific productivity of 1.2 mmol h ؊1 g (dry weight) ؊1 . This illustrates a high rate of L-serine formation and also utilization in the C. glutamicum wild type. Therefore, metabolic engineering of L-serine production from glucose can be achieved only by addressing the apparent key position of this amino acid in the central metabolism.The demand of L-serine is about 300 tons per year, and this amino acid is required for the pharmaceutical and the cosmetic industries, in addition to being a building block for chemical and biochemical purposes (6). The current production relies mainly on its enzymatic or cellular conversion from the precursor glycine plus a C 1 compound. Utilizing the condensing activity of serine hydroxymethyltransferase, an enzymatic system has been elaborated to convert glycine plus formaldehyde to L-serine (15). The cellular systems employed, among others, resting cells of methanol-utilizing bacteria such as Hyphomicrobium methylovorum where L-serine accumulation from glycine plus methanol was achieved (16). Also, a fermentative production of L-serine from glycine alone by Corynebacterium glycinophilum was described (19). However, there is not much information on the direct fermentative production of L-serine from glucose. Attempts to isolate L-serine-producing strains using different bacteria by applying undirected mutagenesis yielded mutants accumulating only traces of L-serine (38). Apparently, the direct conversion of glucose is a demanding challenge, probably due to the role of L-serine as a central intermediate for a number of cellular reactions (Fig. 1).We are interested in the amino acid-synthesizing capabilities of Corynebacterium glutamicum, which is traditionally used for the large-scale production of L-glutamate and L-lysine (9). In general, the efforts to engineer producing strains were focused on the enzymes of the biosynthesis pathways. For instance, con...

The amino acid L-serine is required for pharmaceutical purposes, and the availability of a sugar-based microbial process for its production is desirable. However, a number of intracellular utilization routes prevent overproduction of L-serine, with the essential serine hydroxymethyltransferase (SHMT) (glyA) probably occupying a key position. We found that constructs of Corynebacterium glutamicum strains where chromosomal glyA expression is dependent on P tac and lacI Q are unstable, acquiring mutations in lacI Q , for instance. To overcome the inconvenient glyA expression control, we instead considered controlling SHMT activity by the availability of 5,6,7,8-tetrahydrofolate (THF). The pabAB and pabC genes of THF synthesis were identified and deleted in C. glutamicum, and the resulting strains were shown to require folate or 4-aminobenzoate for growth. Whereas the C. glutamicum ⌬sdaA strain (pserACB) accumulates only traces of L-serine, with the C. glutamicum ⌬pabABC⌬sdaA strain (pserACB), L-serine accumulation and growth responded in a dose-dependent manner to an external folate supply. At 0.1 mM folate, 81 mM L-serine accumulated. In a 20-liter controlled fed-batch culture, a 345 mM L-serine accumulation was achieved. Thus, an efficient and highly competitive process for microbial L-serine production is available.L-Serine is a nonessential amino acid but plays an important role in stabilizing the blood sugar concentration in the liver (16). It relates, furthermore, to many other substances, including sphingosine and the phosphatides, which are part of the myelin covering of the nerves, as well as the formation of activated C 1 units used for a number of anabolic processes (20). Therefore, L-serine is present in selected infusion solutions and also has other applications. For instance, it is an ingredient of skin lotions to ensure a proper hydration status. The total annual demand for L-serine is estimated to be 300 tons (5).The production processes currently used still rely on the extraction of L-serine from protein hydrolysates or from molasses, as well as on the enzymological conversion of glycine plus a C 1 compound, like methanol, to L-serine. The latter uses the reverse reaction of the serine hydroxymethyltransferase (SHMT) (6). Thus, an enzymatic system has been designed to convert glycine plus formaldehyde to L-serine (4). The cellular systems assayed employed, among other things, resting cells of methanol-utilizing bacteria, such as Hyphomicrobium methylovorum, where L-serine formation from glycine plus methanol was achieved (6). In such a system, up to 45 g liter Ϫ1 L-serine accumulation was possible, but only at a glycine yield of 50%, thus making the system less attractive. Also, alginate-entrapped cells of Corynebacterium glycinophilum were used for L-serine formation from glycine (21). It is self-evident that it would be most profitable to directly convert cheap sugar into L-serine. Although microbial processes for amino acid production are in general advancing quickly, attempts to develop L-serin...

It is a classical result of Wigner that for an hermitian matrix with independent entries on and above the diagonal, the mean empirical eigenvalue distribution converges weakly to the semicircle law as matrix size tends to infinity. In this paper, we prove analogs of Wigner's theorem for random matrices taken from all infinitesimal versions of classical symmetric spaces. This is a class of models which contains those studied by Wigner and Dyson, along with seven others arising in condensed matter physics. Like Wigner's, our results are universal in that they only depend on certain assumptions about the moments of the matrix entries, but not on the specifics of their distributions. What is more, we allow for a certain amount of dependence among the matrix entries, in the spirit of a recent generalization of Wigner's theorem, due to Schenker and Schulz-Baldes. As a byproduct, we obtain a universality result for sample covariance matrices with dependent entries.

We prove a large deviations principle for the empirical measures of a class of biorthogonal and multiple orthogonal polynomial ensembles that includes biorthogonal Laguerre, Jacobi and Hermite ensembles, the matrix model of Lueck, Sommers and Zirnbauer for disordered bosons, the Stieltjes-Wigert matrix model of Chern-Simons theory, and Angelesco ensembles.

We study random vectors of the form (Tr(A (1) V ), . . . , Tr(A (r) V )), where V is a uniformly distributed element of a matrix version of a classical compact symmetric space, and the A (ν) are deterministic parameter matrices. We show that for increasing matrix sizes these random vectors converge to a joint Gaussian limit, and compute its covariances. This generalizes previous work of Diaconis et al. for Haar distributed matrices from the classical compact groups. The proof uses integration formulas, due to Collins andŚniady, for polynomial functions on the classical compact groups.