An approach to the metabolic degradation of diethylketone (DEK) by Streptococcus equisimilis: Effect of DEK on the growth, biodegradation kinetics and efficiency

Abstract

The degradation of diethylketone by Streptococcus equisimilis was evaluated. The toxicity of diethylketone was assessed evaluating the growth of the bacteria for the range of diethylketone concentration between 0 and 6.4 g L −1. The maximum specific growth rate achieved is 0.555 h −1 at 3.2 g L −1 of initial diethylketone concentration, followed by a slight decrease, suggesting that higher concentrations of diethylketone negatively affect the growth. The biodegradation efficiency (%) obtained was approximately 95%, for all the initial concentrations tested. The kinetic parameters were estimated using Monod, Powell, Haldane and Loung models. The experimental data is well fitted by the Loung and Haldane models, R 2 = 0.98 for both, as compared to Monod model (R 2 = 0.79) and Powell model (R 2 = 0.72). Once the previous intrinsic functions were established, a set of assays was also performed to evaluate the biodegradation of diethylketone using concentrated biomass for initial diethylketone concentrations ranging from 0.8 to 3.9 g L −1 in a bioreactor operating in batch mode with recirculation. These concentrated biomass assays aimed the optimization of operational conditions. The removal percentages obtained were approximately 100%, for all the initial ketone concentrations tested and the biodegradation rate followed the pseudo-second order kinetics. The mechanism involved in the degradation of diethylketone by this microorganism is not completely understood, but an approach to the metabolic degradation pathway was established by the identification of the metabolites involved on the process.

Biosorption of nickel and cadmium in the presence of diethylketone by a Streptococcus equisimilis biofilm supported on vermiculite

“…A blank, containing culture medium and bacteria was used to assess the standard growth of Streptococcus equisimilis. The toxicity of DEK towards S. equisimilis was reported by Costa et al (2014).…”

“…Since Ni(II) starts to precipitate in the form of Ni(OH) 2 at pH of 7.6, it is concluded that the decrease of Ni(II) concentration occurs by biological processes such as biosorption (Espinozo et al, 2012). These processes result from chemical bonds formed between the ion metal and functional groups present on the bacteria surface (phosphate, carbohydrate, amide I and amide II) (Costa et al, 2014).…”

Bioremoval of Ni and Cd in the presence of diethylketone by fungi and by bacteria – A comparative study

“…DEK's toxicity towards Penicillium sp., Alternaria sp. and Streptococcus equisimilis is reported in Costa et al (2014Costa et al ( , 2015.…”

Biosorption of Multicomponent Solutions: A State of the Art of the Understudy Case

“…The increased use of organic compounds in almost, if not all, industrial sectors as well as in household activities and consequent discharge and accumulation into the environment has increased in an extremely significant way in the past years [2,[12][13][14]. Most of these compounds are extremely toxic to humans due to (i) their general carcinogenic and mutagenic properties, (ii) their capacity to form intermediates with the same or even the higher level of toxicity [15] and (iii) their persistence and mobility into the different environmental matrices [7].…”