The mat (or ecp) fimbrial operon is ubiquitous and conserved in Escherichia coli, but its functions remain poorly described. In routine growth media newborn meningitis isolates of E. coli express the meningitis-associated and temperature-regulated (Mat) fimbria, also termed E. coli common pilus (ECP), at 20 6C, and here we show that the six-gene (matABCDEF)-encoded Mat fimbria is needed for temperature-dependent biofilm formation on abiotic surfaces. The matBCDEF deletion mutant of meningitis E. coli IHE 3034 was defective in an early stage of biofilm development and consequently unable to establish a detectable biofilm, contrasting with IHE 3034 derivatives deleted for flagella, type 1 fimbriae or S-fimbriae, which retained the wild-type biofilm phenotype. Furthermore, induced production of Mat fimbriae from expression plasmids enabled biofilm-deficient E. coli K-12 cells to form biofilm at 20 6C. No biofilm was detected with IHE 3034 or MG1655 strains grown at 37 6C. The surface expression of Mat fimbriae and the frequency of Mat-positive cells in the IHE 3034 population from 20 6C were high and remained unaltered during the transition from planktonic to biofilm growth and within the matured biofilm community. Considering the prevalence of the highly conserved mat locus in E. coli genomes, we hypothesize that Mat fimbria-mediated biofilm formation is an ancestral characteristic of E. coli. INTRODUCTIONEscherichia coli is a multifaceted bacterium that colonizes the mammalian intestine as a harmless commensal but also causes a repertoire of intestinal and extraintestinal infectious diseases (Dobrindt, 2005) and survives in the environment (Savageau, 1983). E. coli from the mother and/or the surrounding environment are generally among the earliest colonizers in the oxygenous neonatal gut. During the first months of life a succession of bacterial populations progresses to a complex, more stable and adult-like microbial community dominated by strict anaerobes (Adlerberth & Wold, 2009). However, some E. coli strains are able to persist as a member of the normal microbiota and constitute a major portion of the facultative intestinal flora on adult mucosal surfaces. E. coli also frequently colonizes anatomical locations outside the gastrointestinal tract, e.g. vagina and urinary bladder (Obata-Yasuoka et al., 2002; Rosen et al., 2007). The population structure of E. coli is largely clonal (Ochman & Selander, 1984;Selander et al., 1986), and isolates are frequently categorized into distinct pathogroups according to specific combinations of phenotypic traits. Based on multilocus enzyme electrophoresis, E. coli strains fall into four main phylogenetic groups (designated A, B1, B2 and D), each containing varying proportions of different pathogroups and non-pathogens. E. coli strains resident in childhood and adult microbiota commonly include pathogenic variants (Sarff et al., 1975;Siitonen, 1992), predominantly belonging to the virulenceassociated phylogenetic group B2 (Nowrouzian et al., 2005; Obata-Yasuoka et al., 200...

The common colonization factor of Escherichia coli, the Mat (also termed ECP) fimbria, functions to advance biofilm formation on inert surfaces as well as bacterial adherence to epithelial cells and subsequent colonization. We used global mini-Tn5 transposon mutagenesis to identify novel regulators of biofilm formation by the meningitic E. coli isolate IHE 3034. Of the 4,418 transformants, we found 17 that were impaired in biofilm formation. Most of these mutants were affected in lipopolysaccharide synthesis and were reduced in growth but not in Mat fimbria expression. In contrast, two mutants grew well but did not express Mat fimbria. The insertions in these two mutants were located at different sites of the rcsB gene, which encodes a DNA-binding response regulator of the Rcs response regulon. The mutations abrogated temperature-dependent biofilm formation by IHE 3034, and the phenotype correlated with loss of mat expression. The defect in biofilm formation in the rcsB mutant was reversed upon complementation with rcsB as well as by overexpression of structural mat genes but not by overexpression of the fimbria-specific activator gene matA. Monitoring of the mat operon promoter activity with chromosomal reporter fusions showed that the RcsB protein and an RcsAB box in the mat regulatory region, but not RcsC, RcsD, AckA, and Pta, are essential for initiation of mat transcription. Gel retardation assays showed that RcsB specifically binds to the mat promoter DNA, which enables its function in promoting biofilm formation by E. coli. Bacterial growth in biofilm provides many advantages compared to a planktonic lifestyle. In a biofilm, bacteria gain resistance to antimicrobial agents and defense systems of the host as well as better protection from predation and other environmental assaults, such as hydrodynamic shear forces and desiccation (9,20). This protective effect probably explains why bacterial biofilm growth is common in many environmental, clinical, and industrial settings and why it complicates the elimination of biofilmassociated bacteria. Following initial attachment to a surface, bacterial cells undergo profound physiological and metabolic adjustments along the transition from a single-cell state into a communal lifestyle. This complex process of biofilm development requires integration of a variety of environmental, cell-to-cell, and intracellular signals into an interplay of regulatory networks (25,50).Escherichia coli is a commensal bacterium in the gastrointestinal tract as well as a pathogen of intra-and extraintestinal body sites. E. coli expresses an arsenal of surface appendages that confer tissue-adhesive and biofilm formation capacity upon the bacterium (27, 28). Meningitis-associated and temperature-regulated (Mat) fimbriae (or E. coli common pili [ECP]) promote biofilm growth on inert surfaces (34) and adhesion to human epithelial cell lines in vitro (4,32,53,55). Available data also indicate that the fimbria is expressed in vivo in the human body and in the intestine of infant mouse (32, 5...

Conversion of dissolved P by ferric sulfate into a particulate form sparingly available to algae was studied in 15 ditches in Finland using stand-alone dispensers for ferric sulfate administration. Ferric sulfate typically converted 60–70 % of dissolved P into iron-associated form, a process which required 250–650 kg per kg dissolved P. Mean cost was 160 EUR per kg P converted (range 20–400 EUR kg−1). The costs were lowest at sites characterized by high dissolved P concentrations and small catchment area. At best, the treatment was efficient and cost-effective, but to limit the costs and the risks, ferric sulfate dispensers should only be installed in small critical source areas.

Cold subarctic pond ecosystems will be threatened due to the increase in global temperatures. Therefore, it is important to gain more knowledge on how their biota may respond to global warming. The aim of this research was to illustrate the variability in diatom species richness and community composition along environmental gradients in northernmost Finland and Norway and reveal the variables most strongly associated with diatom biodiversity. We also compared diatom biodiversity among different biotope types and placed emphasis on the distribution of rare diatom taxa. A total of 100 subarctic ponds from the Finnish and Norwegian Lapland covering an elevational gradient of 8–887 m above sea level were sampled. A generalised linear model and hierarchical partitioning were used to identify variables associated with diatom species richness. To identify variables associated with diatom community composition, a non‐metric multidimensional scaling ordination was performed. Finally, a principal component analysis and permutational multivariate analysis of variance were used for the investigation of environmental and biotic differences among biotope types. Water pH, aluminium concentration, and air temperature best explained the variation in species richness and community composition. Diatom species richness and community composition did not differ among the biotope types, but environmental variables in pine forests differed significantly from other biotope types. Many diatom species occupied the entire elevational gradient, while rare taxa seemed to appear at the ends of the elevational gradient as well around the mid‐elevational zone. We found that elevation was not sufficient to explain the variation in diatom species richness and community composition, but diatom biodiversity was shaped by a variety of local‐scale environmental variables, some of which are in turn correlated with elevation. Our findings suggest that local abiotic factors and especially water chemistry are important factors in describing the variability in diatom community composition and species richness in subarctic ponds. It seems that the lowest and the highest elevations provide suitable habitats for rare diatom taxa that have unique environmental preferences but some of the rare taxa were also constrained to mid elevations. Our study provides new insights into the role of local abiotic variables in shaping subarctic mountain pond biodiversity. We urge researchers not only to study elevational gradients per se in mountain areas, but also pay special attention to environmental covariates that may play a notable role in maintaining freshwater biodiversity in the subarctic.

Agricultural constructed wetlands (CWs) are intended to retain sediment and phosphorus (P) carried off with runoff and drainage water. The accumulated sediment, with adsorbed P, is often advised to be recycled to agricultural land, but little is known about the fertilizer value of sediment‐associated P. This study examined the effects on P adsorption characteristics and P plant availability of mixing CW sediment into soil. Although the total P content in the sediment was approximately equal to that in catchment soil and the NaOH‐extractable P content was higher to that in catchment soil, in adsorption‐desorption tests sediment P solubility decreased and affinity for P increased with increasing addition rate of CW sediment to soil. Already the lowest sediment addition rate (12.5% of dry weight) decreased the equilibrium P concentration (EPC0') by 60% on average compared to unamended catchment soil. In a greenhouse pot experiment, Italian ryegrass (Lolium multiflorum L.) yield was largely unaffected by CW sediment application, but P uptake systematically decreased when the rate of sediment application to soil increased. When 12.5% dry weight of sediment was added, plant P uptake decreased by 6–50% in P‐unfertilized pots and by 6–17% in P‐fertilized pots (150 mg P kg−1) compared with P uptake of ryegrass grown in unamended field soil. Our other results suggest that the plant availability of P in CW sediments is very low due to high clay content and high concentrations of aluminium (Al) and iron (Fe) (hydr)oxides in the sediment. Thus, if applied to agricultural fields in large quantities, dredged CW sediment may impair crop P supply.