Paula S. Duggan

Bio: Paula S. Duggan is an academic researcher from University of Leeds. The author has contributed to research in topics: Hormogonium & Nostoc. The author has an hindex of 9, co-authored 12 publications receiving 745 citations.

Tansley Review No. 107. Heterocyst and akinete differentiation in cyanobacteria

Abstract: Summary 3 I. introduction 4 II. the cyanobacteria 7 III. the heterocyst 9 1. Function and metabolism 9 2. Heterocyst structure 12 (a) Overview 12 (b) The polysaccharide (homogeneous) layer 12 (c) The glycolipid (laminated) layer 12 (d) The septum and microplasmodesmata 12 3. Nitrogen regulation and heterocyst development 12 4. Heterocyst development 13 (a) The proheterocyst 13 (b) Proteolysis associated with heterocyst development 14 (c) RNA polymerase sigma factors 14 (d) Developmental regulation of heterocyst cell wall and nitrogenase gene expression 14 (e) Genome rearrangements associated with heterocyst development 15 5. Genes essential for heterocyst development 15 (a) hetR 15 (b) Protein phosphorylation and the regulation of hetR activity 16 (c) hetR in nonheterocystous cyanobacteria 16 (d) Other heterocyst-specific genes 16 6. Heterocyst spacing 18 (a) Patterns of heterocyst differentiation 18 (b) Genes involved in heterocyst spacing 18 (c) Disruption of heterocyst pattern 18 7. Filament fragmentation and the regression of developing heterocysts 20 8. The nature of the heterocyst inhibitor 20 9. Cell selection during differentiation and pattern formation 20 (a) Cell division 20 (b) DNA replication and the cell cycle 21 (c) Competition 21 10. Models for heterocyst differentiation and pattern control 21 IV. the akinete 23 1. Properties of akinetes 23 2. Structure, composition and metabolism 24 3. Relationship to heterocysts 24 4. Factors that influence akinete differentiation 24 5. Extracellular signals 25 6. Akinete germination 25 7. Genes involved in akinete differentiation 26 V. conclusion 26 Acknowledgements 27 References 28 Cyanobacteria are an ancient and morphologically diverse group of photosynthetic prokaryotes. They were the first organisms to evolve oxygenic photosynthesis, and so changed the Earth's atmosphere from anoxic to oxic. As a consequence, many nitrogen-fixing bacteria became confined to suitable anoxic environmental niches, because the enzyme nitrogenase is highly sensitive to oxygen. However, in the cyanobacteria a number of strategies evolved that protected nitrogenase from oxygen, including a temporal separation of oxygenic photosynthesis and nitrogen fixation and, in some filamentous strains, the differentiation of a specialized cell, the heterocyst, which provided a suitable microaerobic environment for the functioning of nitrogenase. The evolution of a spore-like cell, the akinete, almost certainly preceded that of the heterocyst and, indeed, the akinete may have been the ancestor of the heterocyst. Cyanobacteria have the capacity to differentiate several additional cell and filament types, but this review will concentrate on the heterocyst and the akinete, emphasizing the differentiation and spacing of these specialized cells.

Cyanobacteria–bryophyte symbioses

Abstract: Cyanobacteria are a large group of photosynthetic prokaryotes of enormous environmental importance, being responsible for a large proportion of global CO 2 and N 2 fixation. They form symbiotic associations with a wide range of eukaryotic hosts including plants, fungi, sponges, and protists. The cyanobacterial symbionts are often filamentous and fix N 2 in specialized cells known as heterocysts, enabling them to provide the host with fixed nitrogen and, in the case of non-photosynthetic hosts, with fixed carbon. The best studied cyanobacterial symbioses are those with plants, in which the cyanobacteria can infect the roots, stems, leaves, and, in the case of the liverworts and hornworts, the subject of this review, the thallus. The symbionts are usually Nostoc spp. that gain entry to the host by means of specialized motile filaments known as hormogonia. The host plant releases chemical signals that stimulate hormogonia formation and, by chemoattraction, guide the hormogonia to the point of entry into the plant tissue. Inside the symbiotic cavity, host signals inhibit further hormogonia formation and stimulate heterocyst development and dinitrogen fixation. The cyanobionts undergo morphological and physiological changes, including reduced growth rate and CO 2 fixation, and enhanced N 2 fixation, and release to the plant much of the dinitrogen fixed. This short review summarizes knowledge of the cyanobacterial symbioses with liverworts and hornworts, with particular emphasis on the importance of pili and gliding motility for the symbiotic competence of hormogonia.

Survival of free DNA encoding antibiotic resistance from transgenic maize and the transformation activity of DNA in ovine saliva, ovine rumen fluid and silage effluent

Abstract: To assess the likelihood that the bla gene present in a transgenic maize line may transfer from plant material to the microflora associated with animal feeds, we have examined the survival of free DNA in maize silage effluent, ovine rumen fluid and ovine saliva. Plasmid DNA that had previously been exposed to freshly sampled ovine saliva was capable of transforming competent Escherichia coli cells to ampicillin resistance even after 24 h, implying that DNA released from the diet could provide a source of transforming DNA in the oral cavity of sheep. Although target DNA sequences could be amplified by polymerase chain reaction from plasmid DNA after a 30-min incubation in silage effluent and rumen contents, only short term biological activity, lasting less than 1 min, was observed in these environments, as shown by transformation to antibiotic resistance. These experiments were performed under in vitro conditions; therefore further studies are needed to elucidate the biological significance of free DNA in the rumen and oral cavities of sheep and in silage effluent.

Fate of genetically modified maize DNA in the oral cavity and rumen of sheep.

Abstract: The polymerase chain reaction (PCR) technique was used to investigate the fate of a transgene in the rumen of sheep fed silage and maize grains from an insect-resistant maize line. A 1914-bp DNA fragment containing the entire coding region of the synthetic cryIA(b) gene was still amplifiable from rumen fluid sampled 5 h after feeding maize grains. The same target sequence, however, could not be amplified from rumen fluid sampled from sheep fed silage prepared from the genetically modified maize line. PCR amplification of a shorter (211-bp), yet still highly specific, target sequence was possible with rumen fluid sampled up to 3 and 24 h after feeding silage and maize grains, respectively. These findings indicate that intact transgenes from silage are unlikely to survive significantly in the rumen since a DNA sequence 211-bp long is very unlikely to transmit genetic information. By contrast, DNA in maize grains persists for a significant time and may, therefore, provide a source of transforming DNA in the rumen. In addition, we have examined the biological activity of plasmid DNA that had previously been exposed to the ovine oral cavity. Plasmid extracted from saliva sampled after incubation for 8 min was still capable of transforming competent Escherichia coli to kanamycin resistance, implying that DNA released from the diet within the mouth may retain sufficient biological activity for the transformation of competent oral bacteria.

The fate of antibiotic resistance marker genes in transgenic plant feed material fed to chickens

Abstract: We have examined the fate of an antibiotic resistance marker, incorporated into transgenic maize when fed to chicks. Plant-derived markers were found in the crops of five birds fed transgenic maize and in the stomach contents of two birds. The plant-derived marker gene was not found in the intestines. The survival of the antibiotic resistance marker gene mirrored that of plant DNA targets, demonstrating that it survives no better than other DNA and indicating that it is very unlikely that bacteria in the gut of chickens will be transformed to ampicillin resistance when the birds are fed transgenic maize.

Mechanisms of, and Barriers to, Horizontal Gene Transfer between Bacteria

Abstract: Bacteria evolve rapidly not only by mutation and rapid multiplication, but also by transfer of DNA, which can result in strains with beneficial mutations from more than one parent. Transformation involves the release of naked DNA followed by uptake and recombination. Homologous recombination and DNA-repair processes normally limit this to DNA from similar bacteria. However, if a gene moves onto a broad-host-range plasmid it might be able to spread without the need for recombination. There are barriers to both these processes but they reduce, rather than prevent, gene acquisition.

A complex journey: transmission of microbial symbionts

Abstract: The perpetuation of symbioses through host generations relies on symbiont transmission. Horizontally transmitted symbionts are taken up from the environment anew by each host generation, and vertically transmitted symbionts are most often transferred through the female germ line. Mixed modes also exist. In this Review we describe the journey of symbionts from the initial contact to their final residence. We provide an overview of the molecular mechanisms that mediate symbiont attraction and accumulation, interpartner recognition and selection, as well as symbiont confrontation with the host immune system. We also discuss how the two main transmission modes shape the evolution of the symbiotic partners.

The release of genetically modified crops into the environment. Part II. Overview of ecological risk assessment.

Abstract: Despite numerous future promises, there is a multitude of concerns about the impact of GM crops on the environment. Key issues in the environmental assessment of GM crops are putative invasiveness, vertical or horizontal gene flow, other ecological impacts, effects on biodiversity and the impact of presence of GM material in other products. These are all highly interdisciplinary and complex issues. A crucial component for a proper assessment is defining the appropriate baseline for comparison and decision. For GM crops, the best and most appropriately defined reference point is the impact of plants developed by traditional breeding. The latter is an integral and accepted part of agriculture. In many instances, the putative impacts identified for GM crops are very similar to the impacts of new cultivars derived from traditional breeding. When assessing GM crops relative to existing cultivars, the increased knowledge base underpinning the development of GM crops will provide greater confidence in the assurances plant science can give on the risks of releasing such crops.