Hexavalent chromium reduction by an actinomycete, Arthrobacter crystallopoietes ES 32

Environmental contamination by hexavalent chromium, Cr(VI), presents a serious public health problem. This study assessed the reduction of Cr(VI) by intact cells and a cell-free extract (CFE) of an actinomycete, Arthrobacter crystallopoietes (strain ES 32), isolated from soil contaminated with dichromate. Both intact cells and CFE of A. crystallopoietes, displayed substantial reduction of Cr(VI). Intact cells reduced about 90% of the Cr(VI) added within 12 h and Cr(VI) was almost completely reduced after 24 h. The K _M and V _max of Cr(VI) bioreduction by intact cells were 2.61 μM and 0.0142 μmol/min/mg protein, respectively. Cell-free chromate reductase of the A. crystallopoietes (ES 32) reduced hexavalent chromium at a K _M of 1.78 μM and a V _max of 0.096 μmol/min/mg protein. The rate constant (k) of chromate reduction was inversely related to Cr(VI) concentration and the half-life (t _1/2) of Cr(VI) reduction increased with increasing concentration. A. crystallopoietes produced a periplasmic chromate reductase that was stimulated by NADH. Results indicate that A. crystallopoietes ES 32 can be used to detoxify Cr(VI) in polluted sites, particularly in stressed environments.     

Prp19/Pso4 Is an Autoinhibited Ubiquitin Ligase Activated by Stepwise Assembly of Three Splicing Factors

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A study on the pretreatment of a sugarcane bagasse sample with dilute sulfuric acid

Experiments based on a 2³ central composite full factorial design were carried out in 200-ml stainless-steel containers to study the pretreatment, with dilute sulfuric acid, of a sugarcane bagasse sample obtained from a local sugar–alcohol mill. The independent variables selected for study were temperature, varied from 112.5°C to 157.5°C, residence time, varied from 5.0 to 35.0 min, and sulfuric acid concentration, varied from 0.0% to 3.0% (w/v). Bagasse loading of 15% (w/w) was used in all experiments. Statistical analysis of the experimental results showed that all three independent variables significantly influenced the response variables, namely the bagasse solubilization, efficiency of xylose recovery in the hemicellulosic hydrolysate, efficiency of cellulose enzymatic saccharification, and percentages of cellulose, hemicellulose, and lignin in the pretreated solids. Temperature was the factor that influenced the response variables the most, followed by acid concentration and residence time, in that order. Although harsher pretreatment conditions promoted almost complete removal of the hemicellulosic fraction, the amount of xylose recovered in the hemicellulosic hydrolysate did not exceed 61.8% of the maximum theoretical value. Cellulose enzymatic saccharification was favored by more efficient removal of hemicellulose during the pretreatment. However, detoxification of the hemicellulosic hydrolysate was necessary for better bioconversion of the sugars to ethanol.