Submerged cultures of Aspergillus flavus and Aspergillus niger were grown in a medium containing avidin, a substance which serves as an inhibitor of the conversion of acetate to malonate. Control cultures were grown without the addition of avidin.Analysis of the fatty acids produced by cultures grown in a medium containing avidin gave an increase in C16 fatty acids and a decrease in C18 fatty acids, suggesting that malonate plays an important role in the elongation of long chain fatty acids in these organisms. This effect was observed for five to fifteen hours.Evidence of the conversion of palmitate to stearate to oleate to linoleate was presented. That the conversion of oleate to linoleate involves a desaturase which is highly specific is suggested by the observation that, although there are a number of monoenoic acids present in these organisms, the only dienoic acid found was linoleic acid.

Major interest has focused on the identification of regulatory factors involved in lipid biosynthesis. This study examined the B.napus β-Keto-ACP reductase 5' sequence for potential regulatory cis-acting elements. The 5' sequence of the most highly expressed Brassica napus β-Keto-ACP reductase isoform was fused to the reporter gene β-glucuronidase (GUS) and its expression pattern examined within transgenic Arabidopsis. The construct was shown to act as a functional promoter and direct transcription within embryos, cotyledons and roots. There was no apparent staining within the true leaves, but staining was visible within the cotyledons. Overlapping fragments of the promoter were analysed in gel mobility shift assays and all six showed the formation of protein-DNA complexes. Competition analysis suggested that the same trans-acting factor binds to a number of regions along the promoter. The protein-DNA complex appeared to be competed away by the Arabidopsis enoyl-ACP reductase (EnR) promoter sequence, but not the lipid transfer protein (LTP) promoter. A common 9bp cis-element (CGCANTAAA) was identified in four of the six promoter fragments. Deletion analysis of the β-Keto-ACP reductase promoter intransient expression experiments into B.napus tissue, suggested the promoter could still direct transcription upon deletion to 132bp within embryos. The GUS expression appeared to show more than one decrease in expression upon subsequent deletions of the promoter within embryos, suggesting that more than one cis-element may be involved in the control of transcription. At least one of these suspected decreases con elated with the deletion of one of the 9bp boxes identified. Differences were observed for expression of the constructs within leaves and embryos suggesting that different elements may be involved in transcriptional control within these tissues. The identification of a potential cis-acting element within this study could be used to isolate a potential regulatory trans-acting factor that binds to the B.napus β-Keto-ACP reductase promoter.

No description available.

No description available.

Natural-synthetic hydrid biomaterials have been isolated from the growth of Alcaligenes latus and Pseudomonas oleovorans in the presence of diethylene glycol (DEG). A. latus could cometabolise DEG with 10 g/L glucose, while DEG was consumed by P. oleovorans with 20 mM sodium octanoate or octanoic acid. The presence of DEG in bioprocessing systems for the production of short chain length (scl-) and medium chain length (mcl-) PHAs consequently lowered cell viability and PHA yield. Cell morphology was slightly changed, but the PHA inclusion bodies apparently were not. DEG affected the composition of the mclPHA which was confirmed to be polyhydroxyoctanoate (PHO) with a significant increase in the C8 component. Gas chromatography-mass spectrometry (GC-MS) was used to quantitatively monitor DEG in the system and revealed its cellular adsorption. Intracellularly, the DEG significantly decreased the molar weight of the mclPHA and sclPHA. P1PH NMR, 2-D COSY and HSQC spectra confirmed that the polymer samples consisted of PHA chains terminated by DEG. Similar to the cultivation of P. oleovorans with DEG, the presence of PEG200 and PEG400 also had an effect on cell growth, PHO yield and cell viability. Furthermore, a hybrid copolymer of PHO-PEG200 was synthesised. The synthesis of these natural-synthetic hybrid copolymers could lead the way for a wide variety of PHA-PEG copolymers with a range of bioactive properties. All thermal properties of PHB were higher than those of PHB-DEG. This may be due to a combination of lower PHB molecular weight and termination of the chains by DEG, i.e. ???DEGylation???. However, PHB-DEG was more elastomeric when compared to PHB, showing properties similar to its copolymer with 20 mol% 3-hydroxyvalerate. Contact angles revealed that the PHB-DEG film was slightly more hydrophilic than PHB. Despite the large difference in their respective proportions, the comparatively small DEG component exerted an influence on chain confirmation, such that solvent casting under humid conditions apparently induced self-assembly and formed a disordered microporous film. DEGylation of PHO also had noticeable effects on the physiochemical properties of the biopolymer. A major decrease in molecular weight, together with the termination of hydrophobic PHO chains with hydrophilic end-groups resulted in changes to its thermal properties when compared to PHO. In comparison to PHO, solvent cast films of PHO-DEG were apparently less flexible, but more hydrophilic.

Freshwater cyanobacteria produce a wealth of biologically active metabolites, which can adversely affect human and animal health, and cause great economic damage to the fishing, tourism and water-management industries on a global scale. We describe the molecular genetics and biochemistry of biosynthesis for the cyanobacterial toxic alkaloids cylindrospennopsin, paralytic shellfish toxins (PST) and anatoxin-a. Characterisation of the 43 kb cylindrospennopsin biosynthesis gene cluster (cyr), in Cylindrospermopsis raciborskii AWT205 is described. Biosynthesis is initiated via an amidinotransfer onto glycine followed by five polyketide extensions. Rings are formed via Michael additions, while the uracil ring is formed by a novel mechanism. Tailoring reactions, including sulfation and hydroxylation complete the biosynthesis. We describe the characterisation of PST biosynthesis gene clusters in Anabaena circinalis, Aphanizomenon sp. and Lyngbya wollei. These gene clusters span between 28 and 36 kb and contain genes coding for the biosynthesis and export of PSTs. The Lyngbya wollei PST gene cluster represents a 'natural combinatorial biosynthesis' event, explaining its unique toxin profile. A biosynthetic pathway leading to the formation of saxitoxin and its analogues in these organisms is proposed, and a putative insertion/excision site of the PST gene cluster in Anabaena circinalis 310F was identified. Interestingly, PSTs are produced by distantly related organisms via this unique biosynthesis pathway. We Investigated the phylogenetics of PST biosynthesis genes from four different genera of cyanobacteria. The results suggested that PST biosynthesis in cyanobacteria is an ancient trait, whereby the sporadic distribution of PST production in extant isolates of Anabaena circinalis and Aphanizomenon sp. is a result of the repeated loss of the biosynthetic gene cluster. Horizontal gene ransfer also appears to have had a critical influence on PST biosynthesis in Lyngbya wollei. We additionally propose a hypothetical, mixed non-ribosomal peptide synthetase (NRPS)/polyketide synthase (PKS) biosynthesis scheme for anatoxin-a. Degenerate PCR primers were developed, for the specific amplification of mixed NRPSIPKS hybrid ketosynthase (KS) domains. Gene-walking distally to a novel hybrid KS domain in the anatoxin-a producer Planktothrix rubescens, revealed an orphan gene cluster, denoted pro, which spans 24 kb and codes for a mixed NRPS/PKS system, putatively producing an acetylated and sulphated dipeptide.

Diss. (sammanfattning) Stockholm : Karolinska instituet, 1999. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 6 uppsatser.

Thesis (M.Sc.)--University of Adelaide, Dept. of Biochemistry, 1971.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.