Evolution of Protein Molecules

Cyanobacteria are often the key organisms comprising microbial mats. They form dense micrometer-scale communities in which the full plethora of microbial metabolism can be present. Such mats are therefore excellent model systems and because of their analogy with Precambrian stromatolites they are also attractive subjects for evolutionary studies. Growth and metabolism of the oxygenic phototrophic cyanobacteria enrich the sediment with organic matter. However, in mature mats net growth of cyanobacteria appears to be of less importance. Most of the organic matter produced from photosynthetic CO2 fixation is liberated in the sediment by one of the following: fermentation, photorespiration, pouring out of solutes or secretion of mucus although grazing may also be important. This organic matter is degraded by chemotrophic microorganisms, among which sulphate-reducing bacteria are particularly prominent. The combined activities of the cyanobacteria and sulphate-reducing bacteria result in steep and fluctuating gradients of sulphide and oxygen. Cyanobacteria therefore have to cope with high concentrations of sulphide, oxygen supersaturated – and anoxic conditions. These physicochemical gradients force different functional groups of microorganisms to particular vertical stratified positions in the mat. This, and the fact that accretion of sediment fluctuates, gives rise to one of the most conspicuous properties of microbial mats namely their laminated structure. Modern microbial mats have this laminated structure in common with Precambrian stromatolites. Most modern mats do not lithify but this may also have been the case for Archean microbial mats. Only a few examples of modern calcifying stromatolithic microbial mats are known. A hypothesis has been developed which conceives a role for extracellular polysaccharides in calcification. Extracellular polysaccharides in cyanobacterial mats are often produced as the result of unbalanced growth caused by nitrogen deficiency. The mat organisms are embedded in the extensive polysaccharide matrix that inhibits calcification. All cyanobacterial mats can fix atmospheric dinitrogen, which covers part of their nitrogen demand, but the fluctuating physicochemical gradients limits the efficiency of this process.

Cyanobacterial Mats and Stromatolites

http://www.zebraskimmers.com/pdf_files/metalworking_fluids-mechanisms%20_and_performance_small.pdf

Metalworking fluids—Mechanisms and performance

Sulfur isotope fractionation during bacterial reduction and disproportionation of thiosulfate and sulfite

The objective of this work was to investigate the reaction stoichiometry, kinetics, and mechanism for Cr(VI) reduction by hydrogen sulfide in the aqueous phase Batch experiments with excess [Cr(VI)] over [H2S]T indicated that the molar amount of sulfide required for the reduction of 1 M Cr(VI) was 15, suggesting the following stoichiometry: 2CrO4(2-) + 3H2S + 4H+-->2Cr(OH)3(s) + 3S(s) + 2H2O Further study with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) confirmed that chromium hydroxide and elemental sulfur were the stable products The kinetics of Cr(VI) reduction by hydrogen sulfide was measured under various initial concentrations of Cr(VI) and sulfide as well as pH values controlled by HEPES, phosphate, and borate buffers Results showed that the overall reaction was second-order, ie, first-order with respect to Cr(VI) and first-order to sulfide The reaction rate increased as pH was decreased, and the pH dependence correlated well with the fraction of fully protonated sulfide (H2S) in the pH range of 65-10 The nature of buffers did not influence the reaction rate significantly in the homogeneous system The reaction kinetics could be interpreted by a three-step mechanism: formation of an inner-sphere chromate-sulfide intermediate complex ((H2O4CrVIS)2-), intramolecular electron transfer to form Cr(IV) species, and subsequent fast reactions leading to Cr(III)

Chromium(VI) Reduction by Hydrogen Sulfide in Aqueous Media: Stoichiometry and Kinetics

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods☆

Microbial degradation of water miscible metal working fluids

Determination of low thiourea concentrations in industrial process water and natural samples using reversed-phase high-performance liquid chromatography

Isolation of methanotrophic bacteria from termite gut

Abstract Anaerobic sulphide oxidation in the light was studied with seven cyanobacterial strains isolated from the southern Baltic Sea. All strains oxidized sulphide (1.2-3.5 mM) stoichio-metrically to thiosulphate. No elemental sulphur could be detected as end product of anoxy-genic photosynthesis. Sulphite as intermediate sulphur compound was released into the growth medium during anaerobic sulphide oxidation by these cyanobacteria. The formation of sulphite from sulphide was inhibited by the photosynthesis inhibitor DCMU. The cyanobacterium Oscillatoria sp. strain BO 32 produced another so far not identified intermediate sulphur compound which was probably stored within the cells.

Andreas Rabenstein

Papers

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods☆

Microbial degradation of water miscible metal working fluids

Determination of low thiourea concentrations in industrial process water and natural samples using reversed-phase high-performance liquid chromatography

Isolation of methanotrophic bacteria from termite gut

Sulphite as Intermediate Sulphur Compound in Anaerobic Sulphide Oxidation to Thiosulphate by Marine Cyanobacteria