Kinetics of biodegradation of diethylketone by Arthrobacter viscosus

Optimization of growth and induction conditions for the production of recombinant whole cell cyclohexanone monooxygenase in Escherichia coli

Optimizing biocatalyst production conditions is essential for enhancing productivities and yields in biotransformation applications. This study focused on investigating the impact of the volumetric oxygen mass transfer coefficient (kLa) on the specific growth rate of recombinant E. coli cells and optimizing induction conditions for whole-cell cyclohexanone monooxygenase (CHMO) production. The results demonstrated that elevated kLa improved microbial growth rates, with optimal conditions achieved at kLa = 31 h⁻¹, where aerobic growth is no longer limited by dissolved oxygen. Additionally, the induction of CHMO during the exponential growth phase led to the highest specific biocatalyst activity, when used as resting cells. Further optimization of induction parameters, including the isopropyl-β-D-thiogalactopyranoside (IPTG) concentration and induction duration, significantly increased CHMO activity. The specific activity reached 54.4 U/g, representing an improvement of over 130%. Specifically, optimized conditions included a 5-hour cultivation period at kLa = 31 h⁻¹, resulting in a biocatalyst concentration of approximately 1 g/L, followed by a 20-minute induction with 0.16 mmol/L of IPTG. Bioreactor strategies for a biocatalytic Baeyer-Villiger oxidation process were evaluated, revealing that repeated batch experiments with cell washing between cycles maintained CHMO activity at 53 U/g over multiple cycles, making this the most favorable method for sustained CHMO activity and technology application. This study underscores the importance of induction optimization in maximizing biocatalyst activity for potential pilot-scale applications. These findings provide valuable insights into the optimization of biocatalytic processes, paving the way for enhanced efficiency and productivity in Baeyer-Villiger monooxygenase (BVMO)-driven processes.

Effect of oxygen mass transfer on the kinetics of Baeyer-Villiger oxidation using a recombinant whole-cell biocatalyst

Performance of resting cells of Escherichia coli expressing cyclohexanone monooxygenase was investigated in a Baeyer-Villiger (BV) oxidation. The impact of oxygen mass transfer on bicyclic lactone production and oxygen metabolic consumption was examined at varying biocatalyst and bicyclic ketone concentrations. Initial rate measurements were conducted with oxygen mass transfer coefficient (kLa) ranging from 19 h-1 to 83 h-1. Results varied notably depending on the initial bicyclic ketone concentration. Below 4 g/L, BV oxidation followed zero-order kinetics for the ketone and oxygen. Intrinsic specific rates for bicyclic lactone production and metabolic oxygen consumption were 1.4 mmol/g/h and 1.7 mmol/g/h, respectively. Mass transfer limitations intensified with higher biocatalyst concentrations and lower kLa-values. A refined conceptual model of oxygen demand for metabolism and BV oxidation was proposed. Above 4 g/L, substrate inhibition of BV oxidation was evident, while metabolic oxygen consumption was less affected. Bicyclic ketone consumption rates indicated intracellular ketone accumulation.

Pilot-scale sorption studies of diethylketone in the presence of Cd2+ and Ni2. ENVIRONMENTAL TECHNOLOGY 2019;40:942-953. [PMID: 29187066 DOI: 10.1080/09593330.2017.1411979]

The effect of pH on the sorption capacity of vermiculite towards cadmium and nickel was tested in batch systems and it was shown that the sorption percentages increase with an increase in the mass of vermiculite and with an increase in the initial pH. Maximum sorption percentages were obtained for a pH of 8 and 4 g of vermiculite (86.5% for Cd²⁺ and 86.1% for Ni²⁺, for solutions with 100 mg/L of metal). As a consequence, it was possible to establish a range of optimal pH for biosorption processes, by combining the so determined optimal sorption pH of vermiculite with the optimal growth pH of Streptococcus equisimilis, a bacterium used to treat contaminated water. Pilot-scale experiments with a S. equisimilis biofilm supported on vermiculite were conducted in closed-loop conditions, aiming to treat large volumes of diethylketone aqueous solutions, eventually containing Cd²⁺ or Ni²⁺. The excellent capacity of this joint system to simultaneously biodegrade diethylketone and biosorb Cd²⁺ or Ni²⁺was proved. The removal percentage and the uptake increase through time, even with the replacement of the initial solution by new ones. The breakthrough curves that best describe the results achieved for Cd²⁺ and Ni²⁺ are respectively the Adams-Bohart and the Yoon and Nelson model.

Co-metabolism kinetics and electrogenesis change during cyanide degradation in a microbial fuel cell

The co-metabolic degradation kinetics, microbial growth kinetics and electricity generation capacity were researched of strain MC-1 in a MFC (microbial fuel cell). The results show that Haldane and Aiba models suit the growth kinetics of a single substrate (sodium acetate) MFC with 0.995 correlation coefficient. Moreover, the Haldane model was appropriate to describe the growth kinetics of a single substrate (sodium cyanide) MFC with 0.986 correlation coefficient. The growth kinetics of a mixed substrate MFC can be explained well by the SKIP model with correlation coefficient 0.995. Second order and three-half order models were found to suitably describe the cyanide degradation process. The maximum output voltage of MFC and the cyanide degradation efficiency were significantly enhanced by using sodium acetate and cyanide as mixed substrates. Also, the trend of electricity production is related to the growth cycle of microorganisms in a MFC.

The co-metabolic degradation kinetics, microbial growth kinetics and electricity generation capacity were researched for strain MC-1 in a MFC.

Removal of pharmaceuticals and personal care products by ammonia oxidizing bacteria acclimated in a membrane bioreactor: Contributions of cometabolism and endogenous respiration

We carried out batch experiments using biomass from a membrane bioreactor (MBR) to study the influence of ammonia oxidizing bacteria (AOB) on the removal of 45 pharmaceuticals and personal care products (PPCPs). Kinetic parameters such as biodegradation constants and adsorption coefficients with and without AOB inhibition were estimated. No significant differences in adsorption tendency were found, but the biodegradability of most compounds was enhanced when ammonia was completely oxidized, indicating that AOB present in MBR played a critical role in eliminating the PPCPs. Moreover, target PPCPs were degraded in 2 stages, first by cometabolic degradation related to AOB growth, and then by endogenous respiration by microorganisms in the absence of other growth substrate. The compounds were classified into 3 groups according to removal performance and cometabolic degradation. Our approach provides new insight into the removal of PPCPs via cometabolism and endogenous respiration under AOB enrichment cultures developed in MBR.

Sorption studies of diethylketone in the presence of Al3+, Cd2+, Ni2+ and Mn2+, from lab-scale to pilot scale

The toxic effects of diethylketone (DEK) in aqueous solution with different concentrations of Al³⁺, Cd²⁺, Ni²⁺ and Mn²⁺ were evaluated at lab-scale. It was established that Streptococcus equisimilis is able to efficiently remove DEK with different concentrations with heavy metals. It was proved that this joint-system has excellent capacity to biodegrade high concentrations of DEK in the presence of Al³⁺, Cd²⁺, Ni²⁺ and Mn²⁺. With the exception of Al³⁺, the uptake for all metals increased as the initial concentration of each metal in the mixed solution increased. The breakthrough curves are best described by the Adams and Bohart model for Cd²⁺, by the Yoon and Nelson model for Ni²⁺ and by the Wolborska model for Mn²⁺.

Assessment of Arthrobacter viscosus as reactive medium for forming permeable reactive biobarrier applied to PAHs remediation

Polycyclic aromatic hydrocarbons (PAHs) are significant environmental contaminants as they are present naturally as well as anthropogenically in soil, air and water. In spite of their low solubility, PAHs are spread to the environment, and they are present in surface water, industrial effluent or groundwater. Amongst all remediation technologies for treating groundwater contaminated with PAHs, the use of a permeable reactive biobarrier (PRBB) appears to be the most cost-effective, energy efficient, and environmentally sound approach. In this technology, the microorganisms are used as reactive medium to degrade or stabilize the contaminants. The main limits of this approach are that the microorganisms or consortium used for forming the PRBB should show adequate characteristics. They must be retained in the barrier-forming biofilm, and they should also have degradative ability for the target pollutants. The aim of the present work is to evaluate the viability of Arthrobacter viscosus as bioreactive medium for forming PRBB. Initially, the ability of A. viscosus to remove PAHs, benzo[a]anthracene 100 μM and phenanthrene 100 μM was evaluated operating in a batch bench-scale bioreactor. In both cases, total benzo[a]anthracene and phenanthrene removals were obtained after 7 and 3 days, respectively. Furthermore, the viability of the microorganisms was evaluated in the presence of chromium in a continuous mode. As a final point, the adhesion of A. viscosus to sepiolite forming a bioreactive material to build PRBB was demonstrated. In view of the attained results, it can be concluded that A. viscosus could be a suitable microorganism to form a bioreactive medium for PAHs remediation.

Bioremoval of diethylketone by the synergistic combination of microorganisms and clays: uptake, removal and kinetic studies

The performance of two bacteria, Arthrobacter viscosus and Streptococcus equisimilis, and the effect of the interaction of these bacteria with four different clays on the retention of diethylketone were investigated in batch experiments. The uptake, the removal percentages and the kinetics of the processes were determined. S. equisimilis, by itself, had the best performance in terms of removal percentage, for all the initial diethylketone concentrations tested: 200, 350 and 700 mg/L. The uptake values are similar for both bacteria. A possible mechanism to explain the removal of diethylketone includes its degradation by bacteria, followed by the adsorption of the intermediates/sub-products by the functional groups present on the cells' surfaces. The assays performed with bacteria and clays indicated that the uptake values are similar despite of the clay used, for the same microorganism and mass of clay, but in general, higher values are reached when S. equisimilis is used, compared to A. viscosus. Kinetic data were described by pseudo-first- and pseudo-second-order models.