Microbial retention of mercury from waste streams in a laboratory column containing merA gene bacteria

Abstract: The microorganisms used for the mercury retention experiments were natural isolates and genetically engineered bacteria. All mercury-resistant strains contained the merA gene. Column experiments with these strains were carried out by immobilizing them on different support materials. To obtain kinetic data of the reductase activity for whole cells and the crude extract, batch experiments were carried out under different conditions.     

Cloning and molecular analysis of the poly(3-hydroxybutyric acid) biosynthetic genes of Thiocystis violacea

From a genomic library of Thiocystis violaceae strain 2311 in L47, two adjacent EcoRI restriction fragments of 5361 base pairs (bp) and of 1978 bp were cloned. The 5361-bp EcoRI restriction fragment hybridized with a DNA fragment harbouring the Alcaligenes eutrophus poly(3-hydroxyalkanoate) (PHA) synthase operon (phbCAB) and restored the ability to synthesize and accumulate PHA in PHA-negative mutants derived from A. eutrophus. The nucleotide sequence analysis of both fragments revealed five open-reading frames (ORFs); at least three of them are probably relevant for PHA biosynthesis. The amino acid sequences of the putative proteins deduced from these genes indicate that they encode a -ketothiolase [phbA _Tv, relative molecular mass (M_r) 40850], which exhibited 87.3% amino acid identify with the -ketothiolase from Chromatium vinosum. The amino acid sequences of the putative proteins deduced from ORF2_Tv (M_r 41 450) and phbC _Tv (M_r 39 550), which were located upstream of and antilinear to phbA _Tv, exhibited 74.7% and 87.6% amino acid identify, respectively, with the corresponding gene products of C. vinosum. Downstream of and antilinear to phbC _Tv was located ORF5, which encodes for a protein of high relative molecular mass (M_r 76428) of unknown function. With respect to the divergent organisation of ORF2_Tv and phbC _Tv on one side and of phbA _Tv on the other side and from the homologies of the putative gene products, this region of the T. violaceae genome resembled very much the corresponding region of C. vinosum, which was identified recently. Correspondence to: A. Steinbüchel     

Soils in warmer and less developed countries have less micronutrients globally

Soil micronutrients are capital for the delivery of ecosystem functioning and food provision worldwide. Yet, despite their importance, the global biogeography and ecological drivers of soil micronutrients remain virtually unknown, limiting our capacity to anticipate abrupt unexpected changes in soil micronutrients in the face of climate change. Here, we analyzed >1300 topsoil samples to examine the global distribution of six metallic micronutrients (Cu, Fe, Mn, Zn, Co and Ni) across all continents, climates and vegetation types. We found that warmer arid and tropical ecosystems, present in the least developed countries, sustain the lowest contents of multiple soil micronutrients. We further provide evidence that temperature increases may potentially result in abrupt and simultaneous reductions in the content of multiple soil micronutrients when a temperature threshold of 12–14°C is crossed, which may be occurring on 3% of the planet over the next century. Altogether, our findings provide fundamental understanding of the global distribution of soil micronutrients, with direct implications for the maintenance of ecosystem functioning, rangeland management and food production in the warmest and poorest regions of the planet.     

Translocation of precytochrome C2 into intracytoplasmic membrane vesicles of Rhodobacter capsulatus requires a peripheral membrane protein

Rhodobacter capsulatus is a member of the group α-purple bacteria which are closely related to the ancestral endosymbiont that gave rise to mitochondria. It has therefore been hypothesized that the molecular mechanisms governing protein export in α-purple bacteria have been conserved during the evolution of mitochondria. To enable analysis of protein export in α-purple bacteria we describe here the development of a homologous cell-free synthesis/export system consisting entirely of components of R. capsulatus. Translocation of precytochrome C₂ into intracytoplasmic membrane vesicles of this organism was found to require the proton-motive force and proceed at a significantly higher efficiency when membranes were present during protein synthesis. Furthermore, we show that, in this cell-free system, translocation depends on a preparation of peripheral membrane proteins Which do not possess detectable SecA- and SecB-like actvities.     

Tumor necrosis factors in 1996

The 6th International Congress on Tumor Necrosis Factors and Related Molecules was held in Faliraki, Island of Rhodes, Greece, 8–12 May, 1996. This review summarizes the topics addressed and highlights some of the major advances presented during the meeting.     

Protonation,alkylation, addition and redox reactions of 16, 17 and 18 valence electron [Mo(L)(NO)('S4')] complexes [L = SPh,PMe3, NO; 'S4'2– = 1,2-Bis-(2-mercaptophenylthio)ethane(2-)]

In the quest for complexes modelling functional characteristics of metal sulfur oxidoreductases, a series of molybdenum nitrosyl complexes with sulfur-dominated coordination sphere was synthesized. Treatment of the 16, 17 and 18 valence electron (VE) complexes [Mo(L)(NO)('S₄')] (1–3) [L?=?SPh (1), PMe₃ (2), NO (3), 'S₄'^2–?=?1,2-bis-(2-mercaptophenylthio) ethane(2-)] with the Brönsted acid HBF₄ resulted in formation of different types of products. 1 and 3 were reversibly protonated at one thiolate atom of the 'S₄'^2– ligand;2, however, yielded the phosphonium salt [HPMe₃]BF₄ and the dinuclear [Mo(NO)('S₄')]₂. Alkylation of 1, 2 and 3 by Me₃OBF₄ or Et₃OBF₄ uniformly resulted in high yields of [Mo(L)(NO)(R-'S₄')]BF₄ complexes [L?=?SPh: R?=?Me (5), Et (6); L?=?PMe₃: R?=?Me (7); L?=?NO: R?=?Me (8), Et (9)] in which one thiolate atom of the 'S₄'^2– ligand had become alkylated; the NMR spectra of 5, 6, 8 and 9 indicated that only one out of four theoretically possible diastereoisomers had formed. 5 and 6 were characterized also by single-crystal X-ray structure analyses. A comparison of ν(NO) bands and redox potentials (cyclic voltammetry) of parent complexes and alkylated derivatives showed that alkylation leads to a decrease in electron density at the molybdenum center and to a positive shift in redox potentials. The 16 VE complex 1 could be reduced, also chemically, to give the corresponding 17 VE anion [1]^–, and inserted elemental sulfur into the Mo-SPh bond, forming the 18 VE phenylperthio complex [Mo(η²–SSPh)(NO)('S₄')] (11) which, upon reaction with PPh₃, gave SPPh₃ and regenerated the parent complex 1. These results are discussed with regard to the sequence of proton and electron transfer steps occurring in substrate conversions catalyzed by metal sulfur oxidoreductases.     

Global vegetation models: incorporating transient changes to structure and composition

Abstract. We describe an approach for developing a Dynamic Global Vegetation Model (DGVM) that accounts for transient changes in vegetation distribution over a decadal time scale. The DGVM structure is based on a linkage between an equilibrium global vegetation model and smaller scale ecosystem dynamics modules that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above-ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of forest dieback, is incorporated. We also discuss data needs for the development, calibration and validation of the model.