Fifty‐four bacterial strains belonging to 37 species were tested for their ability to assimilate short chain and/or medium chain liquid n‐alkanes. A gene probe derived from the alkB gene of Pseudomonas oleovorans ATCC 29347 was utilized in hybridization experiments. Results of Southern hybridization of PCR‐amplificates were compared with those of colony hybridization and dot blot hybridization. Strongest signals were received only from Gram‐negative bacteria growing solely with short n‐alkanes (C10). Hybridization results with soil isolates growing with n‐alkanes of different chain lengths suggested as well that alkB genes seem to be widespread only in solely short‐chain n‐alkane‐degrading pseudomonads. PCR products of Rhodococcus sp., Nocardioides sp., Gordona sp. and Sphingomonas sp. growing additionally or solely with medium‐chain n‐alkane as hexadecane had only few sequence identity with alkB though hybridizing with the gene probe. The derived amino acid sequence of the alkB‐amplificate of Pseudomonas aureofaciens showed high homology (95%) with AlkB from Ps. oleovorans. alkB gene disruptants were not able to grow with decane.
An n-alkane-assimilating strain of Candida tropicalis was selected in sandy soil inoculated with microorganisms from contaminated sites. Competition experiments with n-alkane utilizers from different strain collections confirmed that yeasts overgrow bacteria in sandy soil. Acidification of the soil is one of the colonization factors useful for the yeasts. It can be counteracted by addition of bentonite, a clay mineral with high ion exchange capacity, but not, however, by kaolin. Strains of different yeast species showed different levels of competitiveness. Strains of Arxula adeninivorans, Candida maltosa, and Yarrowia lipolytica overgrew strains of C. tropicalis, C. shehatae or Pichia stipitis. Two strains of C. maltosa and Y. lipolytica coexisted during several serial transfers under microcosm conditions.
The composition of microbial communities degrading trimethylolpropaneoleate, a synthetic fatty acid ester, was studied under conditions similar to a frequently used degradation test. A combination of conventional phenotypic tests and molecular biological methods, internal rRNA gene spacer amplification and randomly amplified DNA assay, was used for strain monitoring. Few bacterial species were selected from the large diversity of the inocula during degradation in the batch cultures. Growth depended on activity of extracellular lipases in the bacterial community. However, the enzyme producers made up only a minority. The dominating bacteria were not able to hydrolyze the synthetic ester in pure culture.
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