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A bacterial strain able to produce κ-carrageenase, designated WZUC10, was isolated from a live specimen of the red alga mäçÅ~ãáìã=íÉäÑ~áêá~É collected in the East China Sea. The phylogenetic evidence and phenotypic features indicate that this strain belongs to the genus mëÉìÇç~äíÉêçãçå~ë. WZUC10 requires NaCl for growth and κ-carrageenan to induce κ-carrageenase synthesis; galactose and lactose do not induce it. The optimal growth temperature is 23~27°C. The secreted enzyme, which has a molecular mass of 45 kDa, breaks down κ-carrageenan into κ-neocarratetraose sulfate and larger oligosaccharides with a repeating β-D-Galé4S-(1→4)-α-D-AnGalé structure, but cannot degrade κ-neocarratetraose sulfate or κ-neocarrahexaose sulfate into κ-neocarrabiose sulfate. The enzyme retains 90% of its activity after 2 h at 40°C and is completely inactivated after 7.5 min at 70°C. The enzyme's optimal temperature is 30°C and its optimal pH is 7.5. The enzyme-catalyzed reaction follows Michaelis-Menten kinetics, with the Michaelis constant (h m ) and the turnover number (â) being 0.015 mM and 125 s −1 , respectively. WZUC10 produces 50 U/mL κ-carrageenase after cultivation at 25°C for 35 h on a medium containing 80 g/L glucose, 5 g/L corn steep liquor, 3 g/L κ-carrageenan, and 15 g/L NaCl. κ-Neocarratetraose sulfate was prepared simply with precipitation by ethanol:water (5:1, v/v). © KSBB hÉóïçêÇëW=κJÅ~êê~ÖÉÉå~ëÉI PseudoalteromonasI=ëìäÑ~íÉÇ=çäáÖçë~ÅÅÜ~êáÇÉI=κJåÉçÅ~êê~íÉíê~çëÉI=ÄáçÇÉÖê~Ç~íáçåI=ÅÜ~ê~ÅíÉêáò~íáçå= = = = =

A bacterial isolate (G161) with high Cr(VI)-reducing capacity was isolated from Cr(VI)-contaminated soil and identified as Leucobacter sp. on the basis of 16S rRNA gene sequence analysis. The isolate was a Gram-positive, aerobic rod. The hexavalent chromate-reducing capability of the isolate was investigated under three conditions of oxygen stress. The isolate was found to reduce Cr(VI) under all conditions but performed most effectively during aerobic growth followed by facultative anaerobic incubation. Under these conditions, the isolate tolerated K(2)Cr(2)O(7) concentrations up to 1,000 mg/l and completely reduced 400 mg/l K(2)Cr(2)O(7) within 96 h. The strain reduced Cr(VI) over a wide range of pH (6.0-11.0) and temperatures (15-45 °C) with optimum performance at pH 8.0 and 35 °C. The presence of other metals, such as Ca(2+), Co(2+), Cu(2+), Mn(2+), Ni(2+), and Zn(2+), induced no effect or else played a stimulatory role on Cr(VI)-reduction activity of the strain. The strain was tested for Cr(VI) removal in wastewaters and proved capable of completely reducing the contained Cr(VI). This is the novel report of a bacterial growth and Cr(VI)-reduction process under sequential aerobic growth and facultative anaerobic conditions. The study suggested that the isolate possesses a distinct capability for Cr(VI) reduction which could be harnessed for the detoxification of chromate-contaminated wastewaters.

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