AYŞE KOCA ÇAYDAŞI
MSc Student, Research Assisstant
Dept. of Biological Sciences
Middle East Technical University
Ankara / TURKEY
Mailing Address:
ODTU Biyoloji Bolumu 06531 Ankara TURKEY
e-mail:
aysekoca@hotmail.com
phone:
+90 312 210 51 90
fax:
+90 312 210 79 76
Research Interest
Education
- 1999-2004 BSc, Middle East Technical University, Dept. of Molecular Biology & Genetics, Ankara, Turkey
- 2004-2006 MSc, Middle East Technical University, Dept. of Biology, Ankara, Turkey
Publications
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Yilmaz EI, Caydasi AK, Ozcengiz G (2006) Targeted disruption of homoserine dehydrogenase gene and its effects on cephamycin C production in Streptomyces clavuligerus, (Submitted to Journal of Industrial Microbiology and Biotechnology, Ocak 2007)
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Caydasi AK (27 July 2006), Targeted disruption of homoserine dehydrogenase gene in Streptomyces clavuligerus and its effects on cephamycin C production, M.Sc Thesis, Middle East Technical University, Turkey.
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Taskin, B, Caydasi, AK, Yilmaz, EI and Ozcengiz, G (2006) Aspartate pathway engineering for improving cephamycin C yields in S. clavuligerus. Presented in "2nd FEMS Congress of European Microbiologists" (4-8 July 2006, Madrid). Book of Abstracts. p. 128. (Poster presentation)
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Caydasi AK, Yilmaz EI, Ozcengiz G (2006) Disruption of hom gene of Streptomyces clavuligerus and its effects on cephamycin C production. Presented in “31st FEBS Congress: Molecules in Health and Disease” (24-29 June 2006, Istanbul) The FEBS Journal, vol 273 supplement 1, Abstracts, p.325 (Poster presentation)
M.Sc Thesis Summary:
Title: Targeted disruption of homoserine dehydrogenase gene in Streptomyces clavuligerus and its effects on cephamycin C production
Description: Streptomyces clavuligerus is the producer of medically important β-lactam antibiotics including cephamycin C. The aspartate pathway of S. clavuligerus is an important primary metabolic pathway providing substrates for β-lactam synthesis. α-AAA required for β-lactam synthesis is a catabolic product of L-lys produced from the lysine branch of this pathway. Formation of L-homoserine from aspartate semialdehyde is the first step of the other branch of the pathway leading to L-thr, L-ileu and L-met synthesis and is catalyzed by homoserine dehydrogenase (HSD). The absence of HSD activity in S. clavuligerus was expected to lead to an increase in cephamycin C production levels in two ways. Firstly, all the carbon coming from aspartate would be directed to L-lys. Secondly, concerted feedback inhibition of aspartokinase by L-lys and L-thr would be relieved.
The aim of my thesis study was to disrupt the gene encoding for homoserine dehydrogenase (hom) in S. clavuligerus NRRL 3585 and to investigate the effects of this disruption on cephamycin C yields. For this purpose, a mutant allele was created, carried on a suitable vector and used to replace the chromosomal copy of the target hom gene via double crossing over. Disruption was verified by Southern blot hybridization, PCR, HSD enzyme assay and auxotrophy tests. hom gene disruption resulted in up to 4.3 and 2 fold increase in intracellular free L-lysine concentration and specific cephamycin C production, respectively. In addition, hom disruption caused pleiotropic effects: hom mutants were defective in sporulation and producing a red pigment which was absent from the wild strain. My work in the project also included the optimization of a very effective transformation procedure for S. clavuligerus.
Besides its significance in the antibiotic industry, this study was important for contribution to understanding the link between the primary and secondary metabolism. The study was a good example of metabolic engineering approach to increase the yields of a desired product. Furthermore hom-disrupted mutant of S. clavuligerus will be a good candidate subject for further studies to understand the regulation of morphological and biochemical differentiation in S. clavuligerus.
