Coaggregation between bacteria isolated from tap water : role of extracellular polymeric substances production and evidence of a bridging bacteria

摘要

Six dominant heterotrophic bacteria isolated from tap water coming from a drinkingwater distribution system in the North of Portugal were identified by 16S ribosomalDNA gene sequencing. Their coaggregation partnerships were determined immediatelyafter dual bacteria mixture, 24 h and 48 h later, using the visual coaggregation assay.Interspecies interactions were also analysed by scanning electron microscopy (SEM)and epifluorescence microscopy using a DNA binding stain. Extracellular polymericsubstances – EPS (proteins and polysaccharides) were assessed along time andcorrelated with the coaggregation properties. The bacteria isolated were Acinetobactercalcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacteriummucogenicum, Sphingomonas capsulata, Staphilococcus sp. Only A. calcoaceticuscoaggregated with all the five other strains. The other bacteria had not the ability tocoaggregate in the absence of A. calcoaceticus. Coaggregation after immediate bacteriaassociation was higher for A. calcoaceticus/B. cepacia, being the only interaction thatdecreased coaggregation score along time (24 h and 48 h later). The other interactionsmaintained (A. calcoaceticus/Staphilococcus sp.) and increased (A.calcoaceticus/Methylobacterium sp., A. calcoaceticus/M. mucogenicum, A.calcoaceticus/S. capsulata) coaggregation scores along time. Microscopic analysisrevealed a higher degree of interaction between species than the one obtained by thevisual coaggregation assay. Coaggregation ability was not related with EPS productionbecause the variation along time of the extracellular proteins and polysaccharidescontent seemed not to account for coaggregation phenomenon.Biofilm formation (single and mixed species) studies using an in vitro microplate assayare under running in order to ascertain the function of A. calcoaceticus as bridgingbacteria in biofilm development and to correlate coaggregation results with biofilmformation ability.