Penicillin is historically important as the first discovered drug against bacterial infections in human. Although the penicillin biosyn- thetic pathway and regulatory mechanism have been well studied in Penicillium chrysogenum, the compartmentation and molecular transport of penicillin or its precursors are still poorly understood. In search of the genomic database, more than 830 open reading frames （ORFs） were found to encode transmembrane proteins of P. chrysogenum. In order to investigate their roles on penicillin production, one of them （penT） was selected and cloned. The deduced protein ofpenTbelongs to the major facilitator superfamily （MFS） and contains 12 transmembrane spanning domains （TMS）. During fermentation, the transcription of penT was greatly induced by penicillin precursors phenylacetic acid （PAA） and phenoxyacetic acid （POA）. Knock-down of penT resulted in significant decrease of penicillin production, while over-expression of penT under the promoter of trpC enhanced the penicillin production. Introduction of an additional penT in the wild-type strain of P. chrysogenurn doubled the penicillin production and enhanced the sensitivity of P. chrysogenum to the penicillin precursors PAA or POA. These results indicate that penT stimulates penicillin production probably through enhancing the translocation of penicillin precursors across fungal cellular membrane. Penicillin is historically important as the first discovered drug against bacterial infections in human. Although the penicillin biosyn- thetic pathway and regulatory mechanism have been well studied in Penicillium chrysogenum, the compartmentation and molecular transport of penicillin or its precursors are still poorly understood. In search of the genomic database, more than 830 open reading frames （ORFs） were found to encode transmembrane proteins of P. chrysogenum. In order to investigate their roles on penicillin production, one of them （penT） was selected and cloned. The deduced protein ofpenTbelongs to the
L-Serine plays a critical role as a building block for cell growth, and thus it is difficult to achieve the direct fermentation of L-serine from glucose. In this study, Corynebacterium glutamicum ATCC 13032 was engineered de novo by blocking and attenuating the conversion of L-serine to pyruvate and glycine, releasing the feedback inhibition by L-serine to 3-phosphoglycerate dehydrogenase (PGDH), in combination with the co-expression of 3-phosphoglycerate kinase (PGK) and feedback-resistant PGDH (PGDHr). The resulting strain, SER-8, exhibited a lower specific growth rate and significant differences in L-serine levels from Phase I to Phase V as determined for fed-batch fermentation. The intracellular L-serine pool reached (14.22±1.41) μmol gCDM 1, which was higher than glycine pool, contrary to fermentation with the wild-type strain. Furthermore, metabolic flux analysis demonstrated that the over-expression of PGK directed the flux of the pentose phosphate pathway (PPP) towards the glycolysis pathway (EMP), and the expression of PGDHr improved the L-serine biosynthesis pathway. In addition, the flux from L-serine to glycine dropped by 24%, indicating that the deletion of the activator GlyR resulted in down-regulation of serine hydroxymethyltransferase (SHMT) expression. Taken together, our findings imply that L-serine pool management is fundamental for sustaining the viability of C. glutamicum, and improvement of C1 units generation by introducing the glycine cleavage system (GCV) to degrade the excessive glycine is a promising target for L-serine production in C. glutamicum.
LAI ShuJuanZHANG YunLIU ShuWenLIANG YongSHANG XiuLingCHAI XinWEN TingYi
Three new caryophyllene sesquiterpenoids,cytosporinols A-C(1-3),have been isolated from solid cultures of Cytospora sp.The structures of 1-3 were elucidated primarily by NMR spectroscopy,and 3 was further confirmed by X-ray crystallography.The absolute configurations of the C-11 secondary alcohol in 1 and the 6,8-diol moiety in 3 were deduced using the modified Mosher and Snatzke’s method,respectively.Compounds 2 and 3 showed moderate cytotoxicity against HeLa cells.
Yan LIChang-Wei LICheng-Bin CUIXing-Zhong LIUYong-Sheng CHE
