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J. Bacteriol. doi:10.1128/JB.00930-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Phenotypic Diversification and Adaptation of Serratia marcescens MG1 Biofilm Derived Morphotypes

The Centre for Marine Biofouling and Bio-Innovation, The University of New South Wales, Sydney NSW 2052 Australia; The School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney NSW 2052 Australia; Center for Biomedical Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

^* To whom correspondence should be addressed. Email: S.Kjelleberg{at}unsw.edu.au,

	Abstract

We report here the characterisation of dispersal variants from microcolony-type biofilms of Serratia marcescens MG1. Biofilm formation proceeds through a reproducible process of attachment, aggregation, microcolony development, hollow colony formation, and dispersal. From the time when hollow colonies were observed in flow cell biofilms after 3 - 4 days, at least six different morphological colony variants were consistently isolated from the biofilm effluent. The timing and pattern of variant formation were found to follow a predictable sequence, where some variants, such as a smooth variant with a sticky colony texture (SSV), could be consistently isolated at the time when mature hollow colonies were observed, while a variant which produced copious amounts of capsular polysaccharide (SUMV) was always isolated at late stages of biofilm development and coincided with cell death and biofilm dispersal or sloughing. The morphological variants differed extensively from the wild-type in attachment, biofilm formation, and cell ultrastructure properties. For example, SSV formed two- to three-fold more biofilm biomass than the wild type in batch biofilm assays, despite having a similar growth rate and attachment capacity. Interestingly, the SUMV, and no other variants, was readily isolated from an established SSV biofilm, indicating that the SUMV is a second generation genetic variant derived from SSV. Planktonic cultures showed significantly lower frequencies of variant formation than the biofilms (5.05 x 10^-8 vs. 4.83 x 10^-6 respectively) suggesting that there is strong, diversifying selection occurring within biofilms and that biofilm dispersal involves phenotypic radiation with divergent phenotypes.

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