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Published year: 20154
Effect of organic matter on nitrogenase metal cofactors homeostasis in Azotobacter vinelandii under diazotrophic conditions

Abstract (Expand)

Biological nitrogen fixation can be catalyzed by three isozymes of nitrogenase: Mo-nitrogenase, V-nitrogenase and Fe-nitrogenase. The activity of these isozymes strongly depends on their metal cofactors, … Mo, V and Fe, and their bioavailability in ecosystems. Here, we show how metal bioavailability can be affected by the presence of tannic acid (organic matter), and the subsequent consequences on diazotrophic growth of the soil bacterium Azotobacter vinelandii. In the presence of tannic acids, A. vinelandii produces a higher amount of metallophores, which coincides with an active, regulated and concomitant acquisition of Mo and V under cellular conditions that are usually considered not Mo limiting. The associated nitrogenase genes exhibit decreased nifD expression and increased vnfD expression. Thus, in limiting bioavailable metal conditions, A. vinelandii takes advantage of its nitrogenase diversity to ensure optimal diazotrophic growth.

Authors: C. Jouogo Noumsi, N. Pourhassan, R. Darnajoux, , , V. Burrus, J. P. Bellenger

Date Published: 10th Nov 2015

Publication Type: Not specified

Transformation ofUlva mutabilis(Chlorophyta) by vector plasmids integrating into the genome

Abstract (Expand)

A method for the stable transformation of the green marine macroalga Ulva mutabilis was developed based on vector plasmids integrating into the genome. By combination of the expression signals (promoter, … enhancer, and transcriptional termination sequences) of a chromosomal rbcS gene from U. mutabilis with the bleomycin resistance gene (ble) from Streptoalloteichus hindustanus, a dominant selectable marker gene was constructed for the preparation of a series of E. coli—U. mutabilis shuttle vector plasmids. Special vectors were prepared for the introduction and expression of foreign genes in Ulva, for insertional mutagenesis and gene tagging by plasmid integration into the genome, and for protein tagging by the green fluorescent protein, as well as tools for posttranscriptional gene silencing and cosmid cloning to prepare genomic gene libraries for mutant gene complementation. The vectors were successfully tested in pilot experiments, where they were efficiently introduced into Ulva gametes, zoospores or protoplasts of somatic blade cells by treatment with Ca2+-ions and polyethylene glycol under isotonic conditions at low ionic strength. The parthenogenetically propagated phleomycin-resistant transformants of the mutant slender (sl) and the wildtype (wt) were demonstrated to be carrying the plasmids randomly integrated into the chromosomes often as tandem repeat clusters.

Authors: Wolfgang Oertel, Thomas Wichard, Adelheid Weissgerber

Date Published: 18th Sep 2015

Publication Type: Not specified

The green seaweed Ulva: a model system to study morphogenesis

Abstract (Expand)

Green macroalgae, mostly represented by the Ulvophyceae, the main multicellular branch of the Chlorophyceae, constitute important primary producers of marine and brackish coastal ecosystems. Ulva or … sea lettuce species are some of the most abundant representatives, being ubiquitous in coastal benthic communities around the world. Nonetheless the genus also remains largely understudied. This review highlights Ulva as an exciting novel model organism for studies of algal growth, development and morphogenesis as well as mutualistic interactions. The key reasons that Ulva is potentially such a good model system are: (i) patterns of Ulva development can drive ecologically important events, such as the increasing number of green tides observed worldwide as a result of eutrophication of coastal waters, (ii) Ulva growth is symbiotic, with proper development requiring close association with bacterial epiphytes, (iii) Ulva is extremely developmentally plastic, which can shed light on the transition from simple to complex multicellularity and (iv) Ulva will provide additional information about the evolution of the green lineage.

Authors: , B. Charrier, F. Mineur, J. H. Bothwell, O. D. Clerck, J. C. Coates

Date Published: 19th Feb 2015

Publication Type: Not specified

Regulation of gametogenesis and zoosporogenesis in Ulva linza (Chlorophyta): comparison with Ulva mutabilis and potential for laboratory culture

Abstract (Expand)

Green Ulvophyte macroalgae represent attractive model systems for understanding growth, development, and evolution. They are untapped resources for food, fuel, and high-value compounds, but can also … form nuisance blooms. To fully analyze green seaweed morphogenesis, controlled laboratory-based culture of these organisms is required. To date, only a single Ulvophyte species, Ulva mutabilis Foyn, has been manipulated to complete its whole life cycle in laboratory culture and to grow continuously under axenic conditions. Such cultures are essential to address multiple key questions in Ulva development and in algal-bacterial interactions. Here we show that another Ulva species, U. linza, with a broad geographical distribution, has the potential to be grown in axenic culture similarly to U. mutabilis. U. linza can be reliably induced to sporulate (form gametes and zoospores) in the laboratory, by cutting the relevant thallus tissue into small pieces and removing extracellular inhibitors (sporulation and swarming inhibitors). The germ cells work as an ideal feed stock for standardized algae cultures. The requirement of U. linza for bacterial signals to induce its normal morphology (particularly of the rhizoids) appears to have a species-specific component. The axenic cultures of these two species pave the way for future comparative studies of algal-microbial interactions.

Authors: E. F. Vesty, R. W. Kessler, , J. C. Coates

Date Published: 26th Jan 2015

Publication Type: Not specified

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