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Applied and Environmental Microbiology, April 2008, p. 2511-2517, Vol. 74, No. 8
0099-2240/08/$08.00+0     doi:10.1128/AEM.02229-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Monolayer Adsorption of a "Bald" Mutant of the Highly Adhesive and Hydrophobic Bacterium Acinetobacter sp. Strain Tol 5 to a Hydrocarbon Surface{triangledown}

Katsutoshi Hori,1* Hisami Watanabe,2 Shun'ichi Ishii,2 Yasunori Tanji,2 and Hajime Unno2

Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan,1 Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8501, Japan2

Received 30 September 2007/ Accepted 20 February 2008

The affinity of microbial cells for hydrophobic interfaces is important because it directly affects the efficiency of various bioprocesses, including green biotechnologies. The toluene-degrading bacterium Acinetobacter sp. strain Tol 5 has filamentous appendages and a hydrophobic cell surface, shows high adhesiveness to solid surfaces, and self-agglutinates. A "bald" mutant of this bacterium, strain T1, lacks the filamentous appendages and has decreased adhesiveness but retains a hydrophobic cell surface. We investigated the interaction between T1 cells and an organic solvent dispersed in an aqueous matrix. During a microbial-adhesion-to-hydrocarbon (MATH) test, which is frequently used to measure cell surface hydrophobicity, T1 cells adhered to hexadecane droplet surfaces in a monolayer, whereas wild-type cells aggregated on the droplet surfaces. The adsorbed T1 cells on the hexadecane surfaces hindered the coalescence of the droplets formed by vortexing, stabilizing the emulsion phase. Following the replacement of the aqueous phase with fresh pure water after the MATH test, a proportion of the T1 cells that had adsorbed to the hydrocarbon surface detached during further vortexing, suggesting a reversible adsorption of T1 cells. The final ratio of the adhering cells to the total cells in the detachment test coincided with that in the MATH test. The adhesion of T1 cells to the hydrocarbon surface conformed to the Langmuir adsorption isotherm, which describes reversible monolayer adsorption. Reversible monolayer adsorption should be useful for green technologies employing two-liquid-phase partitioning systems and for bioremediation because it allows effective reaction and transport of hydrophobic substrates at oil-water interfaces.

* Corresponding author. Mailing address: Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan. Phone and fax: 81-52-735-5214. E-mail: hori.katsutoshi{at}nitech.ac.jp

{triangledown} Published ahead of print on 29 February 2008.

Applied and Environmental Microbiology, April 2008, p. 2511-2517, Vol. 74, No. 8
0099-2240/08/$08.00+0     doi:10.1128/AEM.02229-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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