Efficient biodegradation of chlorophenols in aqueous phase by magnetically immobilized aniline-degrading Rhodococcus rhodochrous strain

Abstract

BackgroundChlorophenols are environmental contaminants, which are highly toxic to living beings due to their carcinogenic, mutagenic and cytotoxic properties. Bacterial degradation has been considered a cost-effective and eco-friendly method of removing chlorophenols, compared to the traditional physical–chemical processes.ResultsIn this study, we first developed an efficient process for the biodegradation of chlorophenols by magnetically immobilized Rhodococcus rhodochrous cells. R. rhodochrous DSM6263 degrades chlorophenols following the first step of hydroxylation at the ortho-positions of chlorophenolic rings. The cells immobilized by k-carrageenan with 9 g/L Fe3O4 nanoparticles could efficiently degrade 2-chlorophenol, 4-chlorophenol, 2,3-dichlorophenol and their mixture, which were even higher than those by free cells. The magnetically nanoparticle-immobilized cells could be used at least for six cycles.ConclusionGiven the much easier separation by an external magnetic field and high degradation efficiency, this study provides a promising technique for improving biocatalysts used in the bioremediation process for chlorophenols in wastewater.

Advanced Rhodococcus Biocatalysts for Environmental Biotechnologies

“…As shown by many authors, increased catalytic activities of IC could be a result of their enhanced tolerance to toxic substrates or extended cell loads achieved by immobilization [84,87]. For immobilized rhodococci, enhanced catalytic activities and increased tolerance were reported [13,40,68,[88][89][90][91], as well as the lack of significant differences with SC [70,83,85,[92][93][94][95][96]. In reference [70], the authors clearly demonstrated that, although immobilized Rhodococcus cells were similar to suspended ones and even underperformed them in catalytic activities, immobilization allowed a convenient (+4 • C, no humidity control) and long-term (12 months) storage of biocatalysts without losses in cell viability and functional activity.…”

“…Magnetically immobilized rhodococci oxidized a target compound (2-chlorophenol) four times faster than SC or cells immobilized without magnetic nanoparticles. While particular mechanisms of these effects remain unclear, they are related perhaps to the increased contact area between cells and 2-chlorophenol, thus facilitating the substrate transfer into the cells [96]. In another work [70], rhodococcal cells were entrapped into porous ceramic-like materials.…”

“…Rhodococcus strain(s) Recently, some advanced methods were proposed to immobilize Rhodococcus strains intended for environmental applications. In the work [96], Rhodococcus cells were magnetically held in the κ-carrageenan gel. For this, freshly prepared soft κ-carrageenan gel was mixed with Rhodococcus rhodochrous cells and Fe 3 O 4 nanoparticles and then solidified.…”

“…Various gel-type polymers, both natural (agar, agarose, alginate, κ-carrageenan, and gellan gels) and synthetic (hydroxypropylcellulose, poly(N-isopropylacrylamide), poly(acrylamide), PAAG, and poly(vinylalcohol), PVA) are used for Rhodococcus cell entrapment [83,85,91,96,101,119]. Moreover, the advanced macroporous cryogels (hydroxypropylcellulose, poly(N-isopropylacrylamide), cryo-PAAG, and cryo-PVA) were developed, having a spongy-like structure of large pores (50-200 µm) filled with water and surrounded by thin walls that favors diffusion of molecules and improves equilibrium sorption properties.…”

“…Cryo-PVA has additional advantages over other cryogels, namely high micro-and macroporosity, advanced water-holding capacity, perfect rheological properties, and relatively low biodegradability [77,101]. Among natural gels, κ-carrageenan has increased mechanical, chemical, thermal, and biological stability, and a loosened inner structure favoring substrate transport to bacterial cells [96].…”