No abstract

In California valley grasslands, Avena fatua L. and other exotic annual grasses have largely displaced native perennial bunchgrasses such as Elymus glaucus Buckley and Nassella pulchra (A. Hitchc.) Barkworth. The invasion success and continued dominance of the exotics has been generally attributed to changes in disturbance regimes and the outcome of direct competition between species. Here, we report that exotic grasses can also indirectly increase disease incidence in nearby native grasses. We found that the presence of A. fatua more than doubled incidence of infection by barley and cereal yellow dwarf viruses (B/CYDVs) in E. glaucus. Because B/CYDV infection can stunt E. glaucus and other native bunchgrasses, the indirect effects of A. fatua on virus incidence in natives suggests that apparent competition may be an additional mechanism influencing interactions among exotic and native grasses in California. A. fatua's influence on virus incidence is likely mediated by its effects on populations of aphids that vector B/CYDVs. In our study, aphids consistently preferred exotic annuals as hosts and experienced higher fecundity on them, suggesting that the exotics can attract and amplify vector populations. To the best of our knowledge, these findings are the first demonstration that exotic plants can indirectly influence virus incidence in natives. We suggest that invasion success may be influenced by the capacity of exotic plant species to increase the pathogen loads of native species with which they compete.

A new type of manganese-oxidizing enzyme has been identified in two alphaproteobacteria, "Aurantimonas manganoxydans" strain SI85-9A1 and Erythrobacter sp. strain SD-21. These proteins were identified by tandem mass spectrometry of manganese-oxidizing bands visualized by native polyacrylamide gel electrophoresis in-gel activity assays and fast protein liquid chromatography-purified proteins. Proteins of both alphaproteobacteria contain animal heme peroxidase and hemolysin-type calcium binding domains, with the 350-kDa active Mn-oxidizing protein of A. manganoxydans containing stainable heme. The addition of both Ca 2؉ ions and H 2 O 2 to the enriched protein from Aurantimonas increased manganese oxidation activity 5.9-fold, and the highest activity recorded was 700 M min ؊1 mg ؊1 . Mn(II) is oxidized to Mn(IV) via an Mn(III) intermediate, which is consistent with known manganese peroxidase activity in fungi. The Mn-oxidizing protein in Erythrobacter sp. strain SD-21 is 225 kDa and contains only one peroxidase domain with strong homology to the first 2,000 amino acids of the peroxidase protein from A. manganoxydans. The heme peroxidase has tentatively been named MopA (manganese-oxidizing peroxidase) and sheds new light on the molecular mechanism of Mn oxidation in prokaryotes.

Cortical computations are an emergent property of neural dynamics. To understand how neural dynamics emerges within local cortical networks, we characterized the development and underlying mechanisms of spontaneous dynamics in cortical organotypic slices. We observed not only a quantitative increase in the levels of spontaneous dynamics, but a qualitative transition from brief bursts of activity to well defined Up states during the first 4 weeks in vitro. Analysis of cellular and synaptic properties indicates that these changes are driven by increasing excitatory drive accompanied by changes in the balance of excitation and inhibition. Examination of the structure of spontaneous dynamics revealed no evidence of precisely repeating patterns. Slices exposed to chronic patterned stimulation exhibited decreased levels of spontaneous activity, suggesting homeostatic control of the levels of network activity. Together, these results suggest that Up states reflect a fundamental mode of network dynamics that emerges through the orchestrated regulation of multiple cellular and synaptic properties in parallel.

Initial reactions in anaerobic oxidation of ethylbenzene were investigated in a denitrifying bacterium, strain EB1. Cells of strain EB1 mineralized ethylbenzene to CO 2 under denitrifying conditions, as demonstrated by conversion of 69% of [ 14 C]ethylbenzene to 14 CO 2 . In anaerobic suspensions of strain EB1 cells metabolizing ethylbenzene, the transient formation and consumption of 1-phenylethanol, acetophenone, and an as yet unidentified compound were observed. On the basis of growth experiments and spectroscopic data, the unknown compound is proposed to be benzoyl acetate. Cell suspension experiments using H 2 18 O demonstrated that the hydroxyl group of the first product of anoxic ethylbenzene oxidation, 1-phenylethanol, is derived from water. A tentative pathway for anaerobic ethylbenzene mineralization by strain EB1 is proposed.Anaerobic degradation of aromatic hydrocarbons receives significant attention for the unusual biochemical reactions involved and for its importance in intrinsic bioremediation. Benzene, toluene, ethylbenzene, and xylenes are relevant pollutants resulting from surface spills of gasoline or leaking underground storage tanks (32). Because of their relatively high solubility in water (8) and their toxicity (10, 30), these compounds often come in contact with groundwater and can create a potential health hazard. As oxygen concentrations in groundwater decrease at these sites as a result of degradation of gasoline components by aerobic microorganisms (16, 28), contaminated aquifers become anoxic. Subsequent biological removal of aliphatic and aromatic hydrocarbons at these sites depends on the activity of bacteria capable of metabolizing hydrocarbons under anoxic conditions.In all presently known pathways for mineralization of aromatic hydrocarbons under aerobic conditions, the first oxidation reactions are catalyzed by mono-or dioxygenases (16,31). In oxygenases, molecular oxygen acts as a strong oxidizing agent and is incorporated into the aromatic hydrocarbon (16, 31). The oxygenated aromatic metabolites are then further oxidized via conventional metabolic pathways. Until first postulated in 1984 (27), degradation of aromatic hydrocarbons was not thought to occur in the absence of molecular oxygen. However, in the last 6 years, several pure cultures that are capable of degrading alkylbenzenes under denitrifying (11,12,26,29,35), sulfate-reducing (5, 25), and iron-reducing (20) conditions have been isolated. Evidently, these bacteria are capable of catalyzing the oxidation of aromatic hydrocarbons in the absence of molecular oxygen, yet the biochemical mechanisms underlying the initial enzymatic oxidation reactions are unresolved.We have been investigating the anaerobic degradation of ethylbenzene by a denitrifying bacterium, strain EB1. Strain EB1 was isolated from treatment pond sediment of an oil refinery (3). We report the characterization of strain EB1 and experiments elucidating the first metabolic intermediates formed in anoxic ethylbenzene oxidation. Isolation conditions. Anae...

The first step in anaerobic ethylbenzene mineralization in denitrifying Azoarcus sp. strain EB1 is the oxidation of ethylbenzene to (S)-(؊)-1-phenylethanol. Ethylbenzene dehydrogenase, which catalyzes this reaction, is a unique enzyme in that it mediates the stereoselective hydroxylation of an aromatic hydrocarbon in the absence of molecular oxygen. We purified ethylbenzene dehydrogenase to apparent homogeneity and showed that the enzyme is a heterotrimer (

Microbial Mn(II) oxidation has important biogeochemical consequences in marine, freshwater, and terrestrial environments, but many aspects of the physiology and biochemistry of this process remain obscure. Here, we report genomic insights into Mn(II) oxidation by the marine alphaproteobacterium Aurantimonas sp. strain SI85-9A1, isolated from the oxic/anoxic interface of a stratified fjord. The SI85-9A1 genome harbors the genetic potential for metabolic versatility, with genes for organoheterotrophy, methylotrophy, oxidation of sulfur and carbon monoxide, the ability to grow over a wide range of O 2 concentrations (including microaerobic conditions), and the complete Calvin cycle for carbon fixation. Although no growth could be detected under autotrophic conditions with Mn(II) as the sole electron donor, cultures of SI85-9A1 grown on glycerol are dramatically stimulated by addition of Mn(II), suggesting an energetic benefit from Mn(II) oxidation. A putative Mn(II) oxidase is encoded by duplicated multicopper oxidase genes that have a complex evolutionary history including multiple gene duplication, loss, and ancient horizontal transfer events. The Mn(II) oxidase was most abundant in the extracellular fraction, where it cooccurs with a putative hemolysin-type Ca 2؉ -binding peroxidase. Regulatory elements governing the cellular response to Fe and Mn concentration were identified, and 39 targets of these regulators were detected. The putative Mn(II) oxidase genes were not among the predicted targets, indicating that regulation of Mn(II) oxidation is controlled by other factors yet to be identified. Overall, our results provide novel insights into the physiology and biochemistry of Mn(II) oxidation and reveal a genome specialized for life at the oxic/anoxic interface.

Learning ultimately relies on changes in the flow of activity within neural microcircuits. Plasticity of neural dynamics is particularly relevant for the processing of temporal information. Chronic stimulation of cultured rat cortical networks revealed ‘experience-dependent’ plasticity in neural dynamics. We observed changes in the temporal structure of activity that reflected the intervals used during training, suggesting that cortical circuits are inherently capable of temporal processing on short time scales.