Fungal biotransformation of short-chain n-alkylcycloalkanes.

The cycloalkanes, comprising up to 45% of the hydrocarbon fraction, occur in crude oil or refined oil products (e.g., gasoline) mainly as alkylated cyclohexane derivatives and have been increasingly found in environmental samples of soil and water. Furthermore, short-chain alkylated cycloalkanes are components of the so-called volatile organic compounds (VOCs). This study highlights the biotransformation of methyl- and ethylcyclohexane by the alkane-assimilating yeast Candida maltosa and the phenol- and benzoate-utilizing yeast Trichosporon mucoides under laboratory conditions. In the course of this biotransformation, we detected 25 different metabolites, which were analyzed by HPLC and GC-MS. The biotransformation process of methylcyclohexane in both yeasts involve (A) ring hydroxylation at different positions (C2, C3, and C4) and subsequent oxidation to ketones as well as (B) oxidation of the alkyl side chain to hydroxylated and acid products. The yeast T. mucoides additionally performs ring hydroxylation at the C1-position and (C) oxidative decarboxylation and (D) aromatization of cyclohexanecarboxylic acid. Both yeasts also oxidized the saturated ring system and the side chain of ethylcyclohexane. However, the cyclohexylacetic acid, which was formed, seemed not to be substrate for aromatization. This is the first report of several new transformation reactions of alkylated cycloalkanes for eukaryotic microorganisms.

Agricultural soil and drilosphere as reservoirs of new and unusual assimilators of 2,4-dichlorophenol carbon.

2,4-Dichlorophenol (2,4-DCP) is a potential soil and groundwater contaminant. Earthworms modulate growth and activities of soil microbiota. Thus, active 2,4-DCP degraders in agricultural soil and drilosphere (i.e. burrow walls, gut content and cast) were identified by comparative amplicon pyrosequencing-based 16S rRNA stable isotope probing in soil columns. In situ relevant concentrations of [U-(13) C]2,4-DCP were consumed in soil within 19 and 41 days in the presence and absence of the endogeic earthworm Aporrectodea caliginosa, respectively. [U-(14) C]2,4-DCP mineralization was higher in cast, burrow wall and soil from columns with than without earthworms. [U-(14) C]2,4-DCP mineralization was lowest in gut contents. Data indicated a strong impact of earthworms on the active microbial community. Novosphingobium, Comamonas and Desulfitobacterium sp. assimilated 2,4-DCP-[(13)C] in the absence of earthworms. Pseudomonas, Flavobacterium and Clostridium sp. assimilated 2,4-DCP-[(13)C] in the drilosphere. Novosphingobium- and Variovorax-related taxa dominated [U-(13)C]2,4-DCP consumers in soil slurries with drilosphere and bulk soil material. 16S rRNA sequences suggested species level novelty. The collective data demonstrates that new Bacteroidetes and Alphaproteobacteria/Betaproteobacteria were involved in 2,4-DCP-C transformation and indicated that diverse and hitherto unknown microbes associated with carbon flow from 2,4-DCP are shaped by earthworms.