Assessment of Serratia sp. isolated from iron ore mine in hexavalent chromium reduction: kinetics, fate and variation in cellular morphology

Ultrafast removal of toxic Cr(VI) by the marine bacterium Vibrio natriegens

The fastest-growing microbe Vibrio natriegens is an excellent platform for bioproduction processes. Until now, this marine bacterium has not been examined for bioremediation applications, where the production of substantial amounts of biomass would be beneficial. V. natriegens can perform extracellular electron transfer (EET) to Fe(III) via a single porin-cytochrome circuit conserved in Vibrionaceae. Electroactive microbes capable of EET to Fe(III) usually also reduce toxic metals such as carcinogenic Cr(VI), which is converted to Cr(III), thus decreasing its toxicity and mobility. Here, the performance of V. natriegens was explored for the bioremediation of Cr(VI). At a density of 100 mg/mL, V. natriegens removed 5-20 mg/L Cr(VI) within 30 s and 100 mg/L Cr(VI) within 10 min. In comparison, the model bacterium Escherichia coli grown to a comparable cell density removed Cr(VI) 36 times slower. To eliminate Cr(VI), V. natriegens had to be metabolically active, and functional outer-membrane c-type cytochromes were required. At the end of the Cr(VI) removal process, V. natriegens had reduced all of it into Cr(III) while adsorbing more than half of the metallic ions. These results demonstrate that V. natriegens, with its fast metabolism, is a viable option for the rapid treatment of aqueous pollution with Cr.

Hexavalent chromate bioreduction by a magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1 and the effect of magnetosome synthesis

Magnetotactic bacteria (MTB) are receiving attention for heavy metal biotreatment due to their potential for biosorption with heavy metals and the capability of the magnetic recovery. In this study, we investigated the characteristics of Cr(VI) bioreduction and biosorption by an MTB isolate, Magnetospirillum gryphiswaldense MSR-1, which has a higher growth rate and wider reflexivity in culture conditions. Our results demonstrated that the MSR-1 strain could remove Cr(VI) up to the concentration of 40 mg L^-1 and with an optimal activity at neutral pH conditions. The magnetosome synthesis existed regulatory mechanisms between Cr(VI) reduction and cell division. The addition of 10 mg L^-1 Cr(VI) significantly inhibited cell growth, but the magnetosome-deficient strain, B17316, showed an average specific growth rate of 0.062 h^-1 at the same dosage. Cr(VI) reduction examined by the heat-inactivated and resting cells demonstrated that the main mechanism for MSR-1 strain to reduce Cr(VI) was chromate reductase and adsorption, and magnetosome synthesis would enhance the chromate reductase activity. Finally, our results elucidated that the chromate reductase distributes diversely in multiple subcellular components of the MSR-1 cells, including extracellular, membrane-associated, and intracellular cytoplasmic activity; and expression of the membrane-associated chromate reductase was increased after the cells were pre-exposed by Cr(VI).

Decolorization of Reactive Red 120 by a novel bacterial consortium: Kinetics and heavy metal inhibition study

<abstract><p>Juru River is one of the most polluted rivers in Malaysia. A dye-degrading bacterial consortium has been isolated from the river's sediment. This consortium JR3 consists of <italic>Pseudomonas aeruginosa</italic> MM01, <italic>Enterobacter</italic> sp. MM05 and <italic>Serratia marcescens</italic> MM06, which were able to decolorize up to 700 ppm of the Reactive Red 120 (RR120) dye under optimal conditions with limited substrate available. Substrate inhibition kinetics were investigated, and, based on the best model, Aiba, the maximum growth rate was 0.795 h^–1, while the saturation constant and inhibitory constant were 0.185% and 0.14%, respectively. In addition, the influence of various metal ions on the growth and decolorization rate of this bacterial consortium on RR120 was investigated. Chromium showed the weakest effect on the decolorization of 200 ppm RR120, with 73.5% removal and bacterial growth of 11.461 log CFU mL^–1. Zinc yielded the second weakest effect, followed by silver and lead, with percentages of RR120 decolorization of 63.8%, 54.6% and 50.5%, respectively. Meanwhile, cadmium, arsenic and copper reduced the decolorization of RR120 in consortium JR3 by half. Mercury strongly inhibited decolorization by 32.5%. Based on the least inhibited heavy metal in RR120 decolorization activity of consortium JR3, the best inhibitory kinetic model was Levenspiel, with a maximum growth rate of 0.632 h^–1, while the saturation constant and inhibitory constants were 15.08% and 0.5783%, respectively. The metal-tolerant azo dye-degrading bacterial consortium will be very useful in dye remediation in metal-laden polluted environments.</p></abstract>

Modeling cometabolism of hexavalent chromium by iron reducing bacteria in tertiary substrate system

In this study, a bacterial strain Serratia sp. was employed for the reduction of synthetically prepared different concentration of Cr(VI) solution (10, 25, 40, 50 and 100 mg/L). Cometabolism study have been carried out in the binary substrate system as well as in the tertiary substrate system. The results revealed that when glucose was added as a co-substrate, at low Cr(VI) concentration, complete reduction was achieved followed by increased biomass growth, but when Cr(VI) concentration was increased to 100 mg/L, the reduction decline to 93%. But in presence of high carbon iron filings (HCIF) as co-substrate even at higher Cr(VI) concentration i.e. 100 mg/L, 100% reduction was achieved and the cell growth continued till 124 h. The study was illustrated via Monod growth kinetic model for tertiary substrate system and the kinetic parameters revealed that the HCIF and glucose combination showed least inhibition to hexavalent chromium reduction by Serratia sp.

High carbon iron filings (HCIF) and metal reducing bacteria (Serratia sp.) co-assisted Cr (VI) reduction: Kinetics, mechanism and longevity

Permeable reactive barriers (PRBs) have been an area of interest for in-situ remediation of groundwater. However, the corrosion of iron used in PRBs has been an area of concern. This study was aimed to enhance the long term performance for reduction of Cr (VI) by high carbon iron filings (HCIF) co-assisted with Serratia sp. Cr (VI) reduction by HCIF alone followed pseudo-first order kinetics and the reaction rate was 0.382 h^-1 for 50 mg/L of Cr (VI) which declined to 0.0017 mg^-1 L h^-1 in combined system. But in cyclic studies, the reduction of Cr (VI) with HCIF alone system declined to 70% after 2 cycles whereas more than 90% reduction was observed in combined system up to four cycles. The corrosion potential and XRD data supported that Serratia sp. have positive effect on longevity of HCIF for Cr (VI) reduction.