Sondre Heia - Academia.edu (original) (raw)

Address: Namsos, Nord-Trondelag Fylke, Norway

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Papers by Sondre Heia

Transgenic Research, Apr 25, 2009

The attenuation of disease resistance in transgenic insect-resistant cotton has become one of the... more The attenuation of disease resistance in transgenic insect-resistant cotton has become one of the important factors restricting cotton production in China. Two transgenic insect-resistant cotton lines and their parental conventional cotton lines were used as the testing materials. The effects of root exudates of these cotton lines on the spore germination and mycelial growth of Fusarium oxysporum were studied and the components, contents of amino acids and sugars were determined. The results showed that the resistance of the two insect-resistant cotton lines to F. oxysporum was inferior to the parental lines, and that their root exudates promoted fungal spore germination and mycelial growth. Considerable differences in the components and contents of both, amino acids and sugars were found between the root exudates of transgenic cotton lines and their parental lines, where the disease indices were highly correlated with the total amount of sugars in the root exudates.

Applied and Environmental Microbiology, 2011

Polyene macrolides are important antibiotics used to treat fungal infections in humans. In this w... more Polyene macrolides are important antibiotics used to treat fungal infections in humans. In this work, acyltransferase (AT) domain swaps, mutagenesis, and cross-complementation with heterologous polyketide synthase domain (PKS) loading modules were performed in order to facilitate production of new analogues of the polyene macrolide nystatin. Replacement of AT 0 in the nystatin PKS loading module NysA with the propionate-specific AT 1 from the nystatin PKS NysB, construction of hybrids between NysA and the loading module of rimocidin PKS RimA, and stepwise exchange of specific amino acids in the AT 0 domain by site-directed mutagenesis were accomplished. However, none of the NysA mutants constructed was able to initiate production of new nystatin analogues. Nevertheless, many NysA mutants and hybrids were functional, providing for different levels of nystatin biosynthesis. An interplay between certain residues in AT 0 and an active site residue in the ketosynthase (KS)-like domain of NysA in initiation of nystatin biosynthesis was revealed. Some hybrids between the NysA and RimA loading modules carrying the NysA AT 0 domain were able to prime rimocidin PKS with both acetate and butyrate units upon complementation of a rimA-deficient mutant of the rimocidin/CE-108 producer Streptomyces diastaticus. Expression of the PimS0 loading module from the pimaricin producer in the same host, however, resulted in production of CE-108 only. Taken together, these data indicate relaxed substrate specificity of NysA AT 0 domain, which is counteracted by a strict specificity of the first extender module KS domain in the nystatin PKS of Streptomyces noursei.