Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

Summary: This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N₂ fixation and/or H₂ formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H₂ as a source of combustible energy. To enhance the rates of H₂ production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H₂ formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy.     

Discovery of selective urokinase plasminogen activator (uPA) inhibitors as a potential treatment for multiple sclerosis

We report here the design and synthesis of a novel series of benzylamines that are potent and selective inhibitors of uPA with promising oral availability in rat. Further evaluation of one representative (ZK824859) of the new structural class showed that this compound lowered clinical scores when dosed in either acute or chronic mouse EAE models, suggesting that uPA inhibitors of this type could be useful for the treatment of multiple sclerosis.     

Ecdysteroids: A novel class of anabolic agents?

Increasing numbers of dietary supplements with ecdysteroids are marketed as “natural anabolic agents”. Results of recent studies suggested that their anabolic effect is mediated by estrogen receptor (ER) binding. Within this study the anabolic potency of ecdysterone was compared to well characterized anabolic substances. Effects on the fiber sizes of the soleus muscle in rats as well the diameter of C2C12 derived myotubes were used as biological readouts. Ecdysterone exhibited a strong hypertrophic effect on the fiber size of rat soleus muscle that was found even stronger compared to the test compounds metandienone (dianabol), estradienedione (trenbolox), and SARM S 1, all administered in the same dose (5 mg/kg body weight, for 21 days). In C2C12 myotubes ecdysterone (1 µM) induced a significant increase of the diameter comparable to dihydrotestosterone (1 µM) and IGF 1 (1.3 nM). Molecular docking experiments supported the ERβ mediated action of ecdysterone. To clarify its status in sports, ecdysterone should be considered to be included in the class “S1.2 Other Anabolic Agents” of the list of prohibited substances of the World Anti-Doping Agency.     

Invasion status of Florida bass Micropterus floridanus (Lesueur, 1822) in South Africa

Largemouth bass Micropterus salmoides are a popular North American angling species that was introduced into South Africa in 1928. To enhance the largemouth bass fisheries, Florida bass Micropterus floridanus were introduced into KwaZulu Natal, South Africa, in 1980. Knowledge on the status of M. floridanus in South Africa is required, because it lives longer and reaches larger sizes than M. salmoides, which may result in heightened impacts on native biota. Because M. floridanus are morphologically similar, but genetically distinct from M. salmoides, the distribution of this species was assessed by genetically screening 185 Micropterus sp. individuals sampled from 20 localities across South Africa using the mitochondrial ND2 gene. Individuals with mitochondrial DNA matching M. salmoides were recovered from 16 localities, whereas M. floridanus mitochondrial DNA was recovered from 13 localities. At nine localities (45%), the mitochondrial DNA of both species was detected. These results demonstrate M. floridanus dispersal to multiple sites across South Africa.     

Drought, but not salinity, determines the apparent effectiveness of halophytes colonized by arbuscular mycorrhizal fungi

The halophytes Plantago maritima, Aster tripolium, Artemisia santonicum, Puccinellia limosa, Festuca pseudovina and Lepidium crassifolium from two different saline soils of the Hungarian steppe were examined for colonization by arbuscular mycorrhizal fungi (AMF). The salt aster (A. tripolium) and the sea plantain (P. maritima) were examined more thoroughly by recording root colonization parameters, the salt content in the soil and monthly precipitations in 2001 and 2002. Mycorrhizal colonization was maximal in late spring to early summer and had a second peak later in the autumn. Arbuscule formation and overall mycorrhizal colonization appeared to be inversely correlated with the intensity of rainfall at the investigated sites. The results suggest that, in addition to seasonality, drought may play an important role in governing mycorrhizal activity in saline habitats. In greenhouse experiments, conditions in which AMF could overcome the inhibitory effects of sodium chloride on establishing plant–mycorrhizal symbiosis were not met.     

Possible role of eclosion rhythm in mediating the effects of light-dark environments on pre-adult development in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Background  

In insects, circadian clocks have been implicated in affecting life history traits such as pre-adult development time and adult lifespan. Studies on the period (per) mutants of Drosophila melanogaster, and laboratory-selected lines of Bactrocera cucurbitae suggested a close link between circadian clocks and development time. There is a possibility of clock genes having pleiotropic effects on clock period and pre-adult development time. In order to avoid such pleiotropic effects we have used wild type flies of same genotype under environments of different periodicities, which phenotypically either speeded up or slowed down the eclosion clock of D. melanogaster.     

Transformations of inorganic nitrogen by Azospirillum spp.

Azospirillum spp. participate in all steps of the nitrogen cycle except nitrification. They can fix molecular nitrogen and perform assimilatory nitrate reduction and nitrate respiration. Culture conditions have been defined under which nitrate is used both as terminal respiratory electron acceptor and as nitrogen source for growth. Nitrate and, possibly to a very limited extent, nitrite, but not sulfate, iron or fumarate support anaerobic respiration. Under anaerobic conditions, nitrate can also supply energy for nitrogen fixation but without supporting growth. Nitrate-dependent nitrogenase activity lasts only for 3–4 h until the enzymes of assimilatory nitrate reduction are synthesized. Nitrite accumulates during this period and inhibits nitrogenase activity at concentrations of about 1 mM.     

Genome-wide mapping and prediction suggests presence of local epistasis in a vast elite winter wheat populations adapted to Central Europe

Key message

Genome-wide association mapping as well as marker- and haplotype-based genome-wide selection unraveled a complex genetic architecture of grain yield with absence of large effect QTL and presence of local epistatic effects.

Abstract

The genetic architecture of grain yield determines to a large extent the optimum design of genomic-assisted wheat breeding programs. The main goal of our study was to examine the potential and limitations to dissect the genetic architecture of grain yield in wheat using a large experimental data set. Our study was based on phenotypic information and genomic data of 13,901 SNPs of a diverse set of 3816 elite wheat lines adapted to Central Europe. We applied genome-wide association mapping based on experimental and simulated data sets and performed marker- and haplotype-based genomic prediction. Computer simulations revealed for our mapping population a high power to detect QTL, even if they individually explained only 2.5% of the genetic variation. Despite this, we found no stable marker–trait associations when validating in independent subsets. A two-dimensional scan for marker–marker interactions indicated presence of local epistasis which was further supported by improved prediction abilities when shifting from marker- to haplotype-based genome-wide prediction approaches. We observed that marker effects estimated using genome-wide prediction approaches strongly varied across years albeit resulting in high prediction abilities. Thus, our results suggested that the prediction accuracy of genomic selection in wheat is mainly driven by relatedness rather than by exploiting knowledge of the genetic architecture.

     

Towards growth of arbuscular mycorrhizal fungi independent of a plant host

When surface-sterilized spores of the arbuscular mycorrhizal fungus (AMF) Glomus intraradices Sy167 were germinated on agar plates in the slightly modified minimum mineral medium described by G. Bécard and J. A. Fortin (New Phytol. 108:211-218, 1988), slime-forming bacteria, identified as Paenibacillus validus, frequently grew up. These bacteria were able to support growth of the fungus on the agar plates. In the presence of P. validus, hyphae branched profusely and formed coiled structures. These were much more densely packed than the so-called arbuscule-like structures which are formed by AMF grown in coculture with carrot roots transformed with T-DNA from Agrobacterium rhizogenes. The presence of P. validus alone also enabled G. intraradices to form new spores, mainly at the densely packed hyphal coils. The new spores were not as abundant as and were smaller than those formed by AMF in the monoxenic culture with carrot root tissues, but they also contained lipid droplets and a large number of nuclei. In these experiments P. validus could not be replaced by bacteria such as Escherichia coli K-12 or Azospirillum brasilense Sp7. Although no conditions under which the daughter spores regerminate and colonize plants have been found yet, and no factor(s) from P. validus which stimulates fungal growth has been identified, the present findings might be a significant step forward toward growth of AMF independent of any plant host.