The importance of extracellular DNA (eDNA) in biofilm formation has become increasingly clear from research on clinically relevant bacteria. This study aimed to determine whether the quantity of eDNA produced can be linked to the ability to form biofilm. We systematically quantified eDNA over time during planktonic growth and biofilm formation in Reinheimera sp. F8 and three other environmental isolates belonging to the genera Pseudomonas, Microbacterium and Serratia. eDNA in biofilms was visualised by fluorescence microscopy and quantified by PicoGreen(®) labelling without further sample preparation, whereas eDNA in planktonic cultures was precipitated before labelling and quantification. The effect of eDNA removal was investigated by DNase treatment. eDNA appeared in the early exponential growth phase of planktonic batch cultures and the concentration peaked in the stationary phase. The concentration in biofilms differed substantially between strains and over time during biofilm development. eDNA was important for the initial attachment in all strains, and DNase treatment reduced biofilm formation in three of four strains. The extent to which eDNA accumulated in planktonic cultures or biofilms did not reflect its significance to biofilm formation, and even very low concentrations of eDNA affected biofilm formation strongly. The significance of eDNA for biofilm formation in nature may thus be more widespread than previously anticipated.

Biofilms on food processing equipment cause food spoilage and pose a hazard to consumers. The bacterial community on steel surfaces in a butcher's shop was characterized, and bacteria representative of this community enriched from minced pork were used to study biofilm retention. Stainless steel (SS) was compared to two novel nanostructured sol-gel coatings with differing hydrophobicity. Surfaces were characterized with respect to roughness, hydrophobicity, protein adsorption, biofilm retention, and community composition of the retained bacteria. Fewer bacteria were retained on the sol-gel coated surfaces compared to the rougher SS. However, the two sol-gel coatings did not differ in either protein adsorption, biofilm retention, or microbial community composition. When polished to a roughness similar to sol-gel, the SS was colonized by the same amount of bacteria as the sol-gel, but the bacterial community contained fewer Pseudomonas cells. In conclusion, biofilm retention was affected more by surface roughness than chemical composition under the condition described in this study.

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Multiple independent approaches were applied for monitoring the abundance and identity of sulfate-reducing bacteria (SRB) in pulp of a paper-recycling plant suffering from excessive sulfide emission. The methods applied included most-probable-number (MPN) enumeration of cultivable SRB, rate measurements, FISH and PCR-based retrieval of the functional marker genes dsrA and B (encoding the two major subunits of dissimilatory bisulfite reductase) and 16S rRNA genes. The SRB community was composed of phylogenetically highly different lineages all of low abundance relative to the total microbial community in the pulp, which hampered the applicability of FISH. It was also demonstrated that dsrA- or B-targeted PCR primers commonly used for denaturing gradient gel electrophoresis and real-time PCR analyses were biased. However, using a novel approach combining MPN-PCR and terminal restriction fragment length polymorphism analysis of dsrAB amplicons generated from serially diluted DNA extracts allowed the enumeration and identification of the quantitatively most important members of the SRB community. For fast quantification of SRB in the pulp, the dsrAB-MPN-PCR assay and sulfate reduction rate measurements were found to be most suitable.

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