Jasmonate is involved in the induction of tyrosine aminotransferase and tocopherol biosynthesis in Arabidopsis thaliana

Coronatine-inducible tyrosine aminotransferase (TAT), which catalyses the transamination from tyrosine to p-hydroxyphenylpyruvate, is the first enzyme of a pathway leading via homogentisic acid to plastoquinone and tocopherols, the latter of which are known to be radical scavengers in plants. TAT can be also induced by the octadecanoids methyl jasmonate (MeJA) and methyl-12-oxophytodienoic acid (MeOPDA), as well as by wounding, high light, UV light and the herbicide oxyfluorfen. In order to elucidate the role of octadecanoids in the process of TAT induction in Arabidopsis thaliana (L.) Heynh., the jasmonate-deficient mutant delayed dehiscence (dde1) was used, in which the gene for 12-oxophytodienoic acid reductase 3 is disrupted. The amount of immunodetectable TAT was low. The enzyme was still fully induced by coronatine as well as by MeJA although induction by the latter was to a lesser extent and later than in the wild type. Treatment with MeOPDA, wounding and UV light, however, had hardly any effects. Tocopherol levels that showed considerable increases in the wild type after some treatments were much less affected in the mutant. However, starting levels of tocopherol were higher in non-induced dde1 than in the wild type. We conclude that jasmonate plays an important role in the signal transduction pathway regulating TAT activity and the biosynthesis of its product tocopherol.     

New and fast method to quantify respiration rates of bacterial and plankton communities in freshwater ecosystems by using optical oxygen sensor spots

A new method of respiration rate measurement based on oxygen luminescence quenching in sensor spots was evaluated for the first time for aquatic bacterial communities. The commonly used Winkler and Clark electrode methods to quantify oxygen concentration both require long incubation times, and the latter additionally causes signal drift due to oxygen consumption at the cathode. The sensor spots proved to be advantageous over those methods in terms of precise and quick oxygen measurements in natural bacterial communities, guaranteeing a respiration rate estimate during a time interval short enough to neglect variations in organism composition, abundance, and activity. Furthermore, no signal drift occurs during measurements, and respiration rate measurements are reliable even at low temperatures and low oxygen consumption rates. Both a natural bacterioplankton sample and a bacterial isolate from a eutrophic river were evaluated in order to optimize the new method for aquatic microorganisms. A minimum abundance of 2.2 x 10(6) respiring cells ml(-1) of a bacterial isolate was sufficient to obtain a distinct oxygen depletion signal within 20 min at 20 degrees C with the new oxygen sensor spot method. Thus, a culture of a bacterial isolate from a eutrophic river (OW 144; 20 x 10(6) respiring bacteria ml(-1)) decreased the oxygen saturation about 8% within 20 min. The natural bacterioplankton sample respired 2.8% from initially 94% oxygen-saturated water in 30 min. During the growth season in 2005, the planktonic community of a eutrophic river consumed between 0.7 and 15.6 micromol O(2) liter(-1) h(-1). The contribution of bacterial respiration to the total plankton community oxygen consumption varied seasonally between 11 and 100%.     

Native and introduced gastropods in laurel forests on Tenerife,Canary Islands

The introduction of non-native gastropods on islands has repetitively been related to a decline of the endemic fauna. So far, no quantitative information is available even for the native gastropod fauna from the laurel forests (the so-called Laurisilva) of the Canary Islands. Much of the original laurel forest has been logged in recent centuries. Based on vegetation studies, we hypothesized that densities and the number of introduced species decline with the age of the regrowth forests. We sampled 27 sites from which we collected thirty native and seven introduced species. Two introduced species, Milax nigricans and Oxychilus alliarius, were previously not reported from the Canary Islands. Assemblage composition was mainly structured by disturbance history and altitude. Overall species richness was correlated with slope inclination, prevalence of rocky outcrops, amounts of woody debris and leaf litter depth. Densities were correlated with the depth of the litter layer and the extent of herb layer cover and laurel canopy cover. Introduced species occurred in 22 sites but were neither related to native species richness nor to the time that elapsed since forest regrowth. One introduced slug, Lehmannia valentiana, is already wide-spread, with densities strongly related to herb cover. Overall species richness seemed to be the outcome of invasibility, thus factors enhancing species richness likely also enhance invasibility. Although at present introduced species contribute to diversity, the potential competition between introduced slugs and the rich native semi-slug fauna, and the effects of introduced predatory snails (Oxychilus spp. and Testacella maugei) warrant further monitoring.     

The polysialic acid-specific O-acetyltransferase OatC from Neisseria meningitidis serogroup C evolved apart from other bacterial sialate O-acetyltransferases

Neisseria meningitidis serogroup C is a major cause of bacterial meningitis and septicaemia. This human pathogen is protected by a capsule composed of alpha2,9-linked polysialic acid that represents an important virulence factor. In the majority of strains, the capsular polysaccharide is modified by O-acetylation at C-7 or C-8 of the sialic acid residues. The gene encoding the capsule modifying O-acetyltransferase is part of the capsule gene complex and shares no sequence similarities with other proteins. Here, we describe the purification and biochemical characterization of recombinant OatC. The enzyme was found as a homodimer, with the first 34 amino acids forming an efficient oligomerization domain that worked even in a different protein context. Using acetyl-CoA as donor substrate, OatC transferred acetyl groups exclusively onto polysialic acid joined by alpha2,9-linkages and did not act on free or CMP-activated sialic acid. Motif scanning revealed a nucleophile elbow motif (GXS286XGG), which is a hallmark of alpha/beta-hydrolase fold enzymes. In a comprehensive site-directed mutagenesis study, we identified a catalytic triad composed of Ser-286, Asp-376, and His-399. Consistent with a double-displacement mechanism common to alpha/beta-hydrolase fold enzymes, a covalent acetylenzyme intermediate was found. Together with secondary structure prediction highlighting an alpha/beta-hydrolase fold topology, our data provide strong evidence that OatC belongs to the alpha/beta-hydrolase fold family. This clearly distinguishes OatC from all other bacterial sialate O-acetyltransferases known so far because these are members of the hexapeptide repeat family, a class of acyltransferases that adopt a left-handed beta-helix fold and assemble into catalytic trimers.     

<Emphasis Type=Italic>Gammaproteobacteria</Emphasis> as a Possible Source of Eicosapentaenoic Acid in Anoxic Intertidal Sediments

Eicosapentaenoic acid (EPA; n-20:5ω3) was found to be a constituent of phospholipids in three mesophilic strains of Gammaproteobacteria, which were isolated from anoxic most probable number series prepared with sediments from an intertidal flat of the German North Sea coast. Their partial 16S rRNA gene sequences identified the isolates as close relatives of Shewanella colwelliana, Vibrio splendidus, and Photobacterium lipolyticum. So far, eicosapentaenoic acid has mainly been reported to occur in eukaryotes and some piezophilic or psychrophilic bacteria. With decreasing temperature, relative contents of EPA (up to 14% of total fatty acids) increased in all strains. Additionally, Shewanella and Vibrio spp. showed a significant increase in monounsaturated fatty acids with lower growth temperature. Analysis of the phospholipid compositions revealed that EPA was present in all three major phospholipid types, namely, phosphatidyl glycerol (PG), cardiolipin and phosphatidyl ethanolamine (PE). However, EPA was enriched in PG and cardiolipin relative to PE. In the tidal flat sediments from which the isolates were obtained, substantial amounts of EPA-containing PG were detected, whereas other typical microeukaryotic phospholipids—being also a possible source of EPA—were abundant at the sediment surface but were present in clearly lower amounts in the anoxic layers beneath 5 cm depth. Therefore, the EPA-containing PG species in the deeper layers in these sediments may indicate the presence of Gammaproteobacteria closely related to the isolates. These bacteria appear to be an important source of EPA in buried, anoxic sediments beneath the layers harboring significant populations of benthic eukaryotes.