Assessment of changes in biodiversity when a community of ultramicrobacteria isolated from groundwater is stimulated to form a biofilm

This combination of molecular-based and metabolic-based methods expanded th e insight into monitoring the changes in bacterial biodiversity.The stimula tion of groundwater bacteria to form biofilms, for the remediation of pollu ted aquifers, is subjected to environmental regulations that include measur ement of effects on microbial biodiversity. Groundwater microorganisms cont ain a proportion of unidentified and uncharacterized ultramicrobacteria (UM B) that might play a major role in the bioclogging of geological materials. This study aimed to assess the changes in genetic and metabolic biodiversi ty when a community of UMB, isolated from groundwater, is stimulated to for m biofilms on a ceramic surface. UMB were stimulated with aerobic condition s and injection of molasses, in reactors reproducing groundwater compositio n and temperature. Concentration of planktonic viable UMB, secretion of ext racellular polymeric substances (EPS), and biofilm thickness were monitored . The assessment of changes in biodiversity was achieved by comparing the i nitial UMB community to the biofilm community, using the single strand conf ormational polymorphism (SSCP) method, the cloning and sequencing of 16S rR NA gene (16S rDNA) sequences, and the Biolog microplate system. The hypothe sis stating that indigenous UMB would play a significant role of in the bio film development was corroborated. Within 13 days of stimulation, the UMB p roduced 700 mg L-1 of planktonic EPS and formed a biofilm up to a thickness of 1100 mum. This stimulation led to a decrease in genetic diversity and a n increase in metabolic diversity. The decrease in genetic diversity was sh own by a reduced number of single strand DNA fragments in the SSCP profiles . As such, 16S rDNA sequences from the biofilm revealed the predominance of four bacterial groups: Zoogloea, Bacillus/Paenibacillus, Enterobacteriacea e, and Pseudomonads. A significant increase in metabolic diversity was show n by a highest substrate richness profile and a lower substrate evenness pr ofile of the biofilm bacterial population (p = 0.0 and p = 0.09, respective ly). This higher metabolic diversity might be a consequence of the stimulat ion that seemed to favor the growth of bacteria having a high nutritional v ersatility. Stimulation of UMB, isolated from groundwater, was effective to form a biofilm having a high metabolic biodiversity.