Microfluidically supported characterization of responses of Rhodococcus erythropolis strains isolated from different soils on Cu-, Ni-, and Co-stress

Jialan Cao,Charmi Chande,Michael Köhler,Franziska Kalensee,Tim Schüler

doi:10.1007/s42770-021-00495-2

Abstract

We present a new methodological approach for the assessment of the susceptibility of Rhodococcus erythropolis strains from specific sampling sites in response to increasing heavy metal concentration (Cu2+, Ni2+, and Co2+) using the droplet-based microfluid technique. All isolates belong to the species R. erythropolis identified by Sanger sequencing of the 16S rRNA. The tiny step-wise variation of metal concentrations from zero to the lower mM range in 500 nL droplets not only provided accurate data for critical metal ion concentrations but also resulted in a detailed visualization of the concentration-dependent response of bacterial growth and autofluorescence activity. As a result, some of the isolates showed similar characteristics in heavy metal tolerance against Cu2+, Ni2+, and Co2+. However, significantly different heavy metal tolerances were found for other strains. Surprisingly, samples from the surface soil of ancient copper mining areas supplied mostly strains with a moderate sensitivity to Cu2+, Ni2+, and Co2+, but in contrast, a soil sample from an excavation site of a medieval city that had been covered for about eight centuries showed an extremely high tolerance against cobalt ion (up to 36 mM). The differences among the strains not only may be regarded as results of adaptation to the different environmental conditions faced by the strains in nature but also seem to be related to ancient human activities and temporal partial decoupling of soil elements from the surface. This investigation confirmed that microfluidic screening offers empirical characterization of properties from same species which has been isolated from sites known to have different human activities in the past.

Highlights

Closed-loop processes are one of the most important challenges for a sustainable material management
Among the numerous of microorganisms, the genus Rhodococcus has attracted a lot of interest during the last decades due to the ability of several strains for bioremediation of phenol, dye, fuel, or solvent-contaminated soils [3,4,5,6]
Bacteria as R. erythropolis can promote the bioremediation by direct utilization of organic contaminants as well as by supporting the bioflocculation process [7]

Summary

Introduction

Closed-loop processes are one of the most important challenges for a sustainable material management. Among the numerous of microorganisms, the genus Rhodococcus has attracted a lot of interest during the last decades due to the ability of several strains for bioremediation of phenol-, dye-, fuel-, or solvent-contaminated soils [3,4,5,6]. Bacteria as R. erythropolis can promote the bioremediation by direct utilization of organic contaminants as well as by supporting the bioflocculation process [7]. Rhodococcus is of interest for the degradation of crude oil [9], is usable for the desulfurization of fuels [10], and can play an important role in the bio-recycling of lignocellulose, which is very crucial for the usage of renewable materials [11]. Rhodococcus can be applied for the production of biosurfactants [16, 17] and for the transformation of terpenes usable in the production of fragrances [18] and in the modification of steroids, which is important for drug production [19]

Methods

Results

Conclusion