The epimerization step that converts isopenicillin N into penicillin N during cephalosporin biosynthesis has remained uncharacterized despite its industrial relevance. A transcriptional analysis of a 9-kb region located downstream of the pcbC gene revealed the presence of two transcripts that correspond to the genes named cefD1 and cefD2 encoding proteins with high similarity to long chain acyl-CoA synthetases and acylCoA racemases from Mus musculus, Homo sapiens, and Rattus norvegicus. Both genes are expressed in opposite orientations from a bidirectional promoter region. Targeted inactivation of cefD1 and cefD2 was achieved by the two-marker gene replacement procedure. Disrupted strains lacked isopenicillin N epimerase activity, were blocked in cephalosporin C production, and accumulated isopenicillin N. Complementation in trans of the disrupted nonproducer mutant with both genes restored epimerase activity and cephalosporin biosynthesis. However, when cefD1 or cefD2 were introduced separately into the double-disrupted mutant, no epimerase activity was detected, indicating that the concerted action of both proteins encoded by cefD1 and cefD2 is required for epimerization of isopenicillin N into penicillin N. This epimerization system occurs in eukaryotic cells and is entirely different from the known epimerization systems involved in the biosynthesis of bacterial ␤-lactam antibiotics.The molecular genetics of cephalosporin biosynthesis is an excellent model for secondary metabolism, since considerable information on the enzymology (reviewed in Refs. 1 and 2), molecular genetics, and gene expression mechanisms (3-5) has accumulated in the last few years. The biosynthesis of cephalosporins by Acremonium chrysogenum and cephamycins by Amycolatopsis (Nocardia) lactamdurans and Streptomyces clavuligerus (reviewed in Refs. 6 and 7) begins with the formation1 by the ACV synthetase (8), followed by cyclicization of ACV to isopenicillin N (IPN). IPN is later converted into penicillin N by an epimerase activity that has remained uncharacterized so far in A. chrysogenum. After the epimerization step, penicillin N is transformed by a deacetoxycephalosporin C synthase (expandase) into deacetoxycephalosporin C, and finally, deacetoxycephalosporin C is converted into deacetylcephalosporin C (DAC) and cephalosporin C by DAC synthase (hydroxylase) and DAC acetyltransferase, respectively (Fig. 1).The genes pcbAB (9) and pcbC (10) encoding ACV synthetase and IPN synthase are linked together in chromosome VII in the so-called "early cephalosporin gene cluster" (11). The genes cefEF, encoding the bifunctional expandase-hydroxylase (12), and cefG, encoding the DAC acetyltransferase (13,14), are linked together in the so-called "late cephalosporin cluster" in chromosome I (11).The isopenicillin N epimerization step still remains unclear. Demain and co-workers (15, 16) reported that isopenicillin N was converted into penicillin N by extracts of A. chrysogenum, although the epimerizing enzyme was extremely labile (17, 18), preventing ...

Transcriptional analysis of the region downstream of the pcbAB gene (which encodes the alpha-aminoadipyl-cysteinyl-valine synthetase involved in cephalosporin synthesis) of Acremonium chrysogenum revealed the presence of two different transcripts corresponding to two new ORFs. ORF3 encodes a putative D-hydroxyacid dehydrogenase and cefT (for transmembrane protein) encodes a multidrug efflux pump belonging to the Major Facilitator Superfamily (MFS) of membrane proteins. The CefT protein has 12 transmembrane segments (TMS) and contains motifs A, B, C, D2 and G characteristic of the Drug:H(+) antiporter 12-TMS group of the major facilitator superfamily. The CefT protein confers resistance to some toxic organic acids, including isovaleric acid and phenylacetic acid. Targeted inactivation of ORF3 and cefT by gene replacement showed that they are not essential for cephalosporin biosynthesis. However, amplification of the cefT gene results in increments of up to 100% in cephalosporin production in the A. chrysogenum C10 strain. Amplification of a truncated form of the cefT insert did not lead to cephalosporin overproduction. It seems that the CefT protein is involved in cephalosporin export from A. chrysogenum or in transmembrane signal transduction, and that there are redundant systems involved in cephalosporin export.

Abbreviations: AP, apple polyphenols; DIO, diet-induced obesity; HFS, high-fatsucrose; IPGTT, intraperitoneal glucose tolerance test; RQ, respiratory quotient; WAT, white adipose tissue; HOMA, homeostatic model assessment 1

We conclude that L. fermentum CECT5716 is an efficient treatment for breast pain during lactation associated with a high level of Staphylococcus in breastmilk.

A DNA fragment containing a gene homologous to LYS2 gene of Saccharomyces cerevisiae was cloned from a genomic DNA library of Penicillium chrysogenum AS-P-78. It encodes a protein of 1409 amino acids (Mr 154859) with strong similarity to the S. cerevisiae (49.9% identity) Schizosaccharomyces pombe (51.3% identity) and Candida albicans (48.12% identity) alpha-aminoadipate reductases and a lesser degree of identity to the amino acid-activating domains of the non-ribosomal peptide synthetases, including the alpha-aminoadipate-activating domain of the alpha-aminoadipyl-cysteinyl-valine synthetase of P. chrysogenum (12.4% identical amino acids). The lys2 gene contained one intron in the 5'-region and other in the 3'-region, as shown by comparing the nucleotide sequences of the cDNA and genomic DNA, and was transcribed as a 4.7-kb monocistronic mRNA. The lys2 gene was localized on chromosome III (7.5 Mb) in P. chrysogenum AS-P-78 and on chromosome IV (5.6 Mb) in strain P2, whereas the penicillin gene cluster is known to be located in chromosome I in both strains. The lys2-encoded protein is a member of the aminoacyladenylate-forming enzyme family with a reductase domain in its C-terminal region.

No abstract

Targeted gene disruption efficiency in Acremonium chrysogenum was increased 10-fold by applying the double-marker enrichment technique to this filamentous fungus. Disruption of the mecB gene by the doublemarker technique was achieved in 5% of the transformants screened. Mutants T6 and T24, obtained by gene replacement, showed an inactive mecB gene by Southern blot analysis and no cystathionine-␥-lyase activity. These mutants exhibited lower cephalosporin production than that of the control strain, A. chrysogenum C10, in MDFA medium supplemented with methionine. However, there was no difference in cephalosporin production between parental strain A. chrysogenum C10 and the mutants T6 and T24 in Shen's defined fermentation medium (MDFA) without methionine. These results indicate that the supply of cysteine through the transsulfuration pathway is required for high-level cephalosporin biosynthesis but not for low-level production of this antibiotic in methionine-unsupplemented medium. Therefore, cysteine for cephalosporin biosynthesis in A. chrysogenum derives from the autotrophic (SH 2 ) and the reverse transsulfuration pathways. Levels of methionine induction of the cephalosporin biosynthesis gene pcbC were identical in the parental strain and the mecB mutants, indicating that the induction effect is not mediated by cystathionine-␥-lyase. ␤-Lactam biosynthesis inAcremonium chrysogenum (formerly known as Cephalosporium acremonium) begins with the nonribosomal condensation of the three precursor amino acids L-␣-aminoadipic acid, L-cysteine, and L-valine (1, 21, 23). There are two ways to synthesize cysteine in filamentous fungi (35,26). One pathway, the so-called autotrophic pathway, converts inorganic sulfur to cysteine via serine O-acetyltransferase and O-acetylserine sulfhydrilase (Fig. 1). In the second route, cysteine can be obtained via the reverse transsulfuration pathway, in which the sulfur atom of methionine is transferred to cysteine through S-adenosylmethionine, S-adenosylhomocysteine, homocysteine, and cystathionine as intermediates.The predominant route of the cysteine supply for ␤-lactam biosynthesis depends on the producer microorganism (6). Cysteine for penicillin biosynthesis in Penicillium chrysogenum is obtained mainly from sulfate reduction (31). In this microorganism, the transsulfuration pathway has been considered to have a minor role in penicillin biosynthesis. On the other hand, the sulfur atom for ␤-lactam biosynthesis by A. chrysogenum is believed to derive preferentially from methionine via the reverse transsulfuration pathway (3, 24). However, there is no genetic evidence for, or against, this hypothesis.DL-Methionine is known to stimulate cephalosporin biosynthesis in A. chrysogenum (7, 16). For many years it was unclear whether the stimulatory effect of DL-methionine was due to a precursor effect (one providing cysteine) or to an inducing effect (8,20,23). Sawada and coworkers established that methionine increases isopenicillin N synthase, deacetoxycephalosporin C synthase (30), and ␣-...

Only apple and cinnamon extracts were finally considered as potentially important anti-obesogenic extracts, due to their body fat-lowering effects, while the improvement of obesity-related metabolic complications by apple polyphenols highlights this extract as a promising functional food ingredient for the management of obesity and its metabolic complications.