Colonization and extinction of land planarians (Platyhelminthes,Tricladida) in a Brazilian Atlantic Forest regrowth remnant

Long-term assessments of species assemblages are valuable tools for detecting species ecological preferences and their dispersal tracks, as well as for assessing the possible effects of alien species on native communities. Here we report a 50-year-long study on population dynamics of the four species of land flatworms (Platyhelminthes, Tricladida, Terricola) that have colonized or become extinct in a 70-year-old Atlantic Forest regrowth remnant through the period 1955–2006. On the one hand, the two initially most abundant species, which are native to the study site, Notogynaphallia ernesti and Geoplana multicolor have declined over decades and at present do not exist in the forest remnant. The extinction of these species is most likely related with their preference for open vegetation areas, which presently do not exist in the forest remnant. On the other hand, the neotropical Geoplaninae 1 and the exotic Endeavouria septemlineata were detected in the forest only very recently. The long-term study allowed us to conclude that Geoplaninae 1 was introduced into the study area, although it is only known from the study site. Endeavouria septemlineata, an active predator of the exotic giant African snail, is originally known from Hawaii. This land flatworm species was observed repeatedly in Brazilian anthropogenic areas, and this is the first report of the species in relatively well preserved native forest, which may be evidence of an ongoing adaptive process. Monitoring of its geographic spread and its ecological role would be a good practice for preventing potential damaging effects, since it also feeds on native mollusk fauna, as we observed in lab conditions. Júlio Pedroni: Granted by CNPQ–Brazil.     

Short communication: Screening of native and foreign Bradyrhizobium japonicum strains for high N2 fixation in soybean

Four local rhizobia isolates selected after two screening experiments and five USDA Bradyrhizobium japonicum strains were estimated for N₂ fixation in soybean using the ¹⁵N isotope dilution technique. Strain USDA 110 was superior to the local isolates in nodulation and N₂ fixation when inoculated onto soybean cv TGX 1497-ID in a Nigerian soil and could therefore be used as an inoculant for enhanced N₂ fixation in soybean in Nigeria.     

Uptake and oxidation of aromatic substrates by Rhizobium leguminosarum MNF 3841 and Rhizobium trifolii TA1

Abstract Rhizobium trifolii TA1 and Rhizobium leguminosarum MNF 3841 grow on a range of aromatic substrates. R. trifolii TA1 possesses enzymes of both the catechol and protocatechuate pathways, whereas R. leguminosarum MNF 3841 only has enzymes of the latter pathway. The pathways are induced by growth on benzoate or 4-hydroxybenzoate, respectively, but they are not cross-inducible. 4-Hydroxybenzoate permease and hydroxylase are induced by growth on 4-hydroxybenzoate but not on protocatechuate, suggesting that they are regulated separately from protocatechuate dioxygenase. The uptake systems for both benzoate and 4-hydroxybenzoate are inhibited by azide, carbonyl cyanide m -chlorophenyl hydrazone and N , N '-dicyclohexylcarbodiimide but are insensitive to arsenate. Salicylate and protocatechuate interfere with benzoate and 4-hydroxybenzoate uptake, respectively.     

Chemical studies on the lipopolysaccharide of Rhizobium meliloti 10406 and its lipid A region

The structure of the lipopolysaccharide from Rhizobium meliloti 10406, a derivative of the wild-type strain MVII-1, was examined. The compositional analysis of its polysaccharide moiety demonstrated lack of heptose(s), but high contents in glucose, galacturonic acid and 2-keto-3-deoxy-octonate (dOclA) as characteristic features. The lipid A moiety consisted of a -1,6 linked glucosamine disaccharide carrying ester (at C-4) and glycosidically (at C-1) linked phosphate residues, both present exclusively as monoester phosphates but not as phosphodiesters. Ester- and amidelinked 3-hydroxy fatty acids were mostly present as non-3-O-acylated residues. Laser desorption mass spectrometry (LD-MS) revealed heterogeneity in the fatty acid substitution, as was also indicated by the non-stoichiometric ratios obtained by quantitative fatty acid analysis. The predominating lipid A structure contained at the reducing glucosamine residue ester-linked 3-hydroxy-tetradecanoic acid (3-OH-14:0) and amide-linked 3-OH-18:0, or 3-OH-18:1, respectively. The distal (non-reducing) glucosamine carried ester-bound the recently discovered 27-hydroxyoctacosanoic acid and 3-OH-14:0 and, as amide-linked fatty acid, mostly 3-hydroxy-stearic acid (3-OH-18:0).The isolated lipopolysaccharide exhibited a high extent of lethal toxicity in galactosamine-treated mice, comparable to that of enterobacterial lipopolysaccharide. The structural relationship of LPS and lipid A of Rhizobium meliloti to other rhizobial lipopolysaccharides and lipid A's with respect to questions of taxonomy and of phylogenetic relationships will be discussed.Abbreviations LPS lipopolysaccharide - dOclA 3-deoxy-D-mannooctulosonic acid (KDO) - GalA galacturonic acid - DOC sodium deoxycholate - PAGE polyacrylamide gel electrophoresis - LD-MS laser desorption-mass spectrometry     

Shifts in symbiotic associations in plants capable of forming multiple root symbioses across a long‐term soil chronosequence

Changes in soil nutrient availability during long‐term ecosystem development influence the relative abundances of plant species with different nutrient‐acquisition strategies. These changes in strategies are observed at the community level, but whether they also occur within individual species remains unknown. Plant species forming multiple root symbioses with arbuscular mycorrhizal (AM) fungi, ectomycorrhizal (ECM) fungi, and nitrogen‐(N) fixing microorganisms provide valuable model systems to examine edaphic controls on symbioses related to nutrient acquisition, while simultaneously controlling for plant host identity. We grew two co‐occurring species, Acacia rostellifera (N₂‐fixing and dual AM and ECM symbioses) and Melaleuca systena (AM and ECM dual symbioses), in three soils of contrasting ages (c. 0.1, 1, and 120 ka) collected along a long‐term dune chronosequence in southwestern Australia. The soils differ in the type and strength of nutrient limitation, with primary productivity being limited by N (0.1 ka), co‐limited by N and phosphorus (P) (1 ka), and by P (120 ka). We hypothesized that (i) within‐species root colonization shifts from AM to ECM with increasing soil age, and that (ii) nodulation declines with increasing soil age, reflecting the shift from N to P limitation along the chronosequence. In both species, we observed a shift from AM to ECM root colonization with increasing soil age. In addition, nodulation in A. rostellifera declined with increasing soil age, consistent with a shift from N to P limitation. Shifts from AM to ECM root colonization reflect strengthening P limitation and an increasing proportion of total soil P in organic forms in older soils. This might occur because ECM fungi can access organic P via extracellular phosphatases, while AM fungi do not use organic P. Our results show that plants can shift their resource allocation to different root symbionts depending on nutrient availability during ecosystem development.     

A rhizobia strain isolated from root nodule of gymnosperm Podocarpus macrophyllus

Symbiotic nitrogen fixation of rhizobia and leguminous plants is considered as the most important biologic nitrogen fixation system on earth. Symbiotic nodulation of gymnosperm Podocarpus macro-phyllus and rhizobia has never been reported. In this study, 11 endophytic bacteria strains were isolated from root nodules of P. macrophyllus and its variation P. macrophyllus var. maki. The plant infection tests on these strains indicated that the isolated strains could be nodulated on P. macrophyllus plants, and weak nitrogenase activity of nodules was found in acetylene reduction method. According to the physiological and biochemical characteristics of the 11 strains, GXLO 02 was selected as the representative strain. 16S rDNA full-length sequence analysis of GXLO 02 confirmed that the representative strain GXLO 02 belongs to Rhizobium sp.     

胡枝子属根瘤菌的多相分类研究

采用了数值分类、全细胞可溶性蛋白电泳分析、ＤＮＡＧ＋Ｃｍｏｌ％和ＤＮＡ相关性的测定以及１６ＳｒＤＮＡＰＣＲＲＦＬＰ分析等多相分类技术对来源于不同地区的１６种寄主的胡枝子根瘤菌进行了系统的分类研究。数值分类的结果表明,在６７％的相似性水平上,全部供试菌可以分为快生型根瘤菌和慢性型根瘤菌两大群,在８０％的相似性水平上又可分为四个亚群。在此基础上,对各亚群的胡枝子根瘤菌进行了ＤＮＡ相关性的测定,以进一步证实和确定它们的分类地位,并通过１６ＳｒＤＮＡＰＣＲＲＦＬＰ分析对各亚群的系统发育关系进行了初步研究。     

Invasive legume management strategies differentially impact mutualist abundance and benefit to native and invasive hosts

Determining the best management practices for plant invasions is a critical, but often elusive goal. Invasive removals frequently involve complex and poorly understood biotic interactions. For example, invasive species can leave potent legacies that influence the success of native species restoration efforts, and positive plant‐microbial feedbacks may promote continued reinvasion by an exotic species following restoration. Removal methods can vary in their effects on plant–soil feedbacks, with consequences for restoration of native species. We determined the effects of invasion by a leguminous shrub (French broom; Genista monspessulana) on the density and community composition of, and benefit conferred by, its microbial mutualists in its invading range. Densities of soil‐dwelling rhizobia were much higher in areas invaded by G. monspessulana relative to uninvaded areas, and this increased density of rhizobia fed back to increase seedling growth of both the invader and native legumes. We further compared how three techniques for removing G. monspessulana affected the densities of rhizobia relative to areas where G. monspessulana was still present. Removal by hand‐pulling reduced soil rhizobial densities, and reduced growth of one native legume, while having no effect on the growth of the invader. Overall, our results show that the consequences of restoration techniques, both above‐ and belowground, could be critical for the successful removal of an invasive legume and restoration of native species.     

Continuous ATP Regeneration Using Immobilized Yeast Cells

Arthrobacter simplex was screened as an α-keto-δ-guanidinovalerate (ketoarginine) assimilating organism. A characteristic feature was its growth on ketoarginine as a carbon source; it began to grow after an extremely long lag. Its growth was stimulated by addition of 0.02% yeast extract to the medium.

The results indicated the transamination of arginine-α-ketoglutarate (α-KGA) and the hydrolyzing reaction of ketoarginine into α-keto-δ-aminovalerate and urea. Two intermediates, ketoarginine and α-keto-δ-aminovalerate, were isolated and identified by various procedures. Coupling of the two reactions was demonstrated in cell-free extracts of arginine-grown cells; ketoarginine formed from arginine by transamination with α-KGA was hydrolyzed directly to α-keto-δ-aminovalerate and urea. The metabolic routes of arginine in microorganisms were discussed.