The emergence of degradative biofilms

Abstract

The aim of this work was to determine the role of cellular recombination and positioning in the emergence of biofilm communities. This involved monitoring a biofilm community cultivated in a flow cell and subjected to cyclic environmental transitions from labile to refractory substrates. Laser microscopy of flow cells revealed that transitions from labile to refractory substrates resulted in a decrease in the thickness and percent area coverage of the biofilm communities. Repeated inoculation of flow cell communities with a composite inoculum resulted in an increase in the number and diversity of emigrants as well as greater thickness and area coverage of the biofilms than when the communities were inoculated only at the beginning of the experiment. This suggested that juxtapositioning through organismal recombination enhanced the growth of biofilm communities subjected to environmental stresses. Repeated environmental cycling also enhanced the growth of biofilm communities, suggesting that the functionality of cellular positioning may have accrued from one cycle to another, representing a form of heritable community-level information. Patterns of emigration that emerged during adaptation of biofilm communities to substrate transitions showed the appearance and disappearance of discrete sets of organisms. In addition, when biofilm communities cultivated using tryptic soy broth (TSB) were plated on benzoate-containing agar, higher plating efficiencies were detected at lower dilutions. This was concomitant with the formation of satellite colonies around primary colonies of benzoate-resistant bacteria. Plating assays and radiolabeled-benzoate mineralization experiments revealed that efficient benzoate degradation by the primary colonies protected the satellite strains against inhibitory concentrations of sodium benzoate. This protection also occurred during batch and flow cell cultivation. When a microbial community derived from a pristine soil environment was subjected to a substrate shift from TSB to benzoate, inclusion of a benzoate-degrading strain of Pseudomonas fluorescens (BD1) enhanced community stability. This suggested that bacteria may respond to environmental stresses as sets of spatially-related organisms as opposed to functioning exclusively as individuals. The emergence of protective synergisms also suggests that strategies based on association between microorganisms should be a consideration in food preservation, human health as well as in biodegradation.