Degradation of a Mixture of Hydrocarbons, Gasoline, and Diesel Oil Additives by Rhodococcus aetherivorans and Rhodococcus wratislaviensis

International audienc

Isolation and characterization of a new Mycobacterium austroafricanum strain, IFP 2015, growing on MTBE

A new Mycobacterium austroafricanum strain, IFP 2015, growing on methyl tert-butyl ether (MTBE) as a sole carbon source was isolated from an MTBE-degrading microcosm inoculated with drain water of an MTBE-supplemented gasoline storage tank. M. austroafricanum IFP 2015 was able to grow on tert-butyl formate, tert-butyl alcohol (TBA) and ?-hydroxyisobutyrate. 2-Methyl-1,2-propanediol was identified as the TBA oxidation product in M. austroafricanum IFP 2015 and in the previously isolated M. austroafricanum IFP 2012. M. austroafricanum IFP 2015 also degraded ethyl tert-butyl ether more rapidly than M. austroafricanum IFP 2012. Specific primers designed to monitor the presence of M. austroafricanum strains could be used as molecular tools to detect similar strains in MTBE-contaminated environment.NRC publication: Ye

Improving isopropanol tolerance and production of Clostridium beijerinckii DSM 6423 by random mutagenesis and genome shuffling

Random mutagenesis and genome shuffling was applied to improve solvent tolerance and isopropanol/butanol/ethanol (IBE) production in the strictly anaerobic bacteria Clostridium beijerinckii DSM 6423. Following chemical mutagenesis with N-methyl-N-nitro-N-nitrosoguanidine (NTG), screening of putatively improved strains was done by submitting the mutants to toxic levels of inhibitory chemicals or by screening for their tolerance to isopropanol (>35 g/L). Suicide substrates, such as ethyl or methyl bromobutyrate or alcohol dehydrogenase inhibitors like allyl alcohol, were tested and, finally, 36 mutants were isolated. The fermentation profiles of these NTG mutant strains were characterized, and the best performing mutants were used for consecutive rounds of genome shuffling. Screening of strains with further enhancement in isopropanol tolerance at each recursive shuffling step was then used to spot additionally improved strains. Three highly tolerant strains were finally isolated and able to withstand up to 50 g/L isopropanol on plates. Even if increased tolerance to the desired end product was not always accompanied by higher production capabilities, some shuffled strains showed increased solvent titers compared to the parental strains and the original C. beijerinckii DSM 6423. This study confirms the efficiency of genome shuffling to generate improved strains toward a desired phenotype such as alcohol tolerance. This tool also offers the possibility of obtaining improved strains of Clostridium species for which targeted genetic engineering approaches have not been described yet

Ethyl tert-butyl ether (ETBE) biodegradation by a syntrophic association of Rhodococcus sp. IFP 2042 and Bradyrhizobium sp. IFP 2049 isolated from a polluted aquifer

International audienceEthyl tert-butyl ether (ETBE) enrichment was obtained by adding contaminated groundwater to a mineral medium containing ETBE as the sole carbon and energy source. ETBE was completely degraded to biomass and CO2 with a transient production of tert-butanol (TBA) and a final biomass yield of 0.37 ± 0.08 mg biomass (dry weight).mg−1 ETBE. Two bacterial strains, IFP 2042 and IFP 2049, were isolated from the enrichment, and their 16S rRNA genes (rrs) were similar to Rhodococcus sp. (99 % similarity to Rhodococcus erythropolis) and Bradyrhizobium sp. (99 % similarity to Bradyrhizobium japonicum), respectively. Rhodococcus sp. IFP 2042 degraded ETBE to TBA, and Bradyrhizobium sp. IFP 2049 degraded TBA to biomass and CO2. A mixed culture of IFP 2042 and IFP 2049 degraded ETBE to CO2 with a biomass yield similar to the original ETBE enrichment (0.31 ± 0.02 mg biomass.mg−1 ETBE). Among the genes previously described to be involved in ETBE, MTBE, and TBA degradation, only alkB was detected in Rhodococcus sp. IFP 2042 by PCR, and none were detected in Bradyrhizobium sp. IFP 2049