Phylogenetic relationships of nonaxenic filamentous cyanobacterial strains based on 16S rRNA sequence analysis

In order to determine the nearly complete 16S rRNA gene sequences of cyanobacteria originating from nonaxenic cultures, a cyanobacterium-specific oligonucleotide probe was developed to distinguish polymerase chain reaction (PCR) products of the cyanobacterial rRNA operons from those resulting from amplification of contaminating bacteria. Using this screening method the 16S rRNA genes of four nonaxenic filamentous cyanobacterial strains belonging to the generaLeptolyngbya andOscillatoria were cloned and sequenced. For the genusLeptolyngbya, the 16S rRNA sequence of the axenic strain PCC 73110 was also determined. Phylogenetic trees were constructed based on complete and partial sequences. The results show that the strainsLeptolyngbya foveolarum Komárek 1964/112,Leptolyngbya sp. VRUC 135 Albertano 1985/1, andLeptolyngbya boryanum PCC 73110 belong to the same cluster. StrainOscillatoria cf.corallinae SAG 8.92, which contains the rare photosynthetic pigment CU-phycoerythrin, is not closely related to other CU-phycoerythrin-containing cyanobacteria.Oscillatoria agardhii CYA 18, which is a representative of planktonicOscillatoria species that form toxic blooms in Norwegian inland waters, has no close relatives in the tree.     

Biofilm formation by different strains of Salmonella typhimurium in artificial systems

The ability of 14 different strains of Salmonella typhimurium to biofilm formation depending on genotype and culture conditions was investigated in artificial systems: in 96-well plastic microtitre plates, plastic and glass tubes, plastic Petri dishes and on microscope glasses. Quantitative biofilm growth was monitored by using an assay based on crystal violet staining, while planctonic growth in the same cultures was monitored by absorbance in iEMS Reader MF, and qualitatively--by digital photo and visually. Optimal rate between growth and biofilm indications for all strains was determined at initial cell concentration 10(6-7) KOE/ml and culture incubation at t degrees 28 degrees C. The nutrient content of the medium significantly influenced the quantity of produced biofilm. The nutrient broth LB without NaCl was more effective in promoting biofilm formation, than LB itself. The least quantity of biofilm was formed in water. The genotype of the strains also critically influenced the quantity of produced biofilm. Nonmotile mutants cells had reduced ability to form biofilm. RpoS mutant cells produced significantly less biofilm as compared with cells of isogenic parent strains. The chemical content of plastic and glass also influenced biofilm formation.     

Biofilm formation by ica-positive and ica-negative strains of Staphylococcus epidermidis in vitro

Staphylococcus epidermidis is a clinically important opportunistic pathogen that forms biofilm infections on nearly all types of indwelling medical devices. The biofilm forming capability of S. epidermidis has been linked to the presence of the ica operon in the genome, and the amount of biofilm formation measured by the crystal violet (CV) adherence assay. Six S. epidermidis strains were characterized for their ica status using PCR, and their biofilm forming ability over 6 days, using the CV assay and a flow cell system. Ica-negative strains characterized as ‘negative for biofilm formation’ based on the CV assay were demonstrated to form strongly attached biofilms after 6 days. However, the biofilms were not as extensive as the ica-positive strains. It was concluded that ica is not required for biofilm formation, nor is the 24-h CV assay generalizable for predicting the 6-day biofilm-forming ability for all S. epidermidis strains.     

Biofilm formation and interactions of bacterial strains found in wastewater treatment systems

Biofilm formation and adherence properties of 13 bacterial strains commonly found in wastewater treatment systems were studied in pure and mixed cultures using a crystal violet microtiter plate assay. Four different culture media were used, wastewater, acetate medium, glucose medium and diluted nutrient broth. The medium composition strongly affected biofilm formation. All strains were able to form pure culture biofilms within 24 h in at least one of the tested culture media and three strains were able to form biofilm in all four culture media, namely Acinetobacter calcoaceticus ATCC 23055, Comamonas denitrificans 123 and Pseudomonas aeruginosa MBL 0199. The adherence properties assessed were initial adherence, cell surface hydrophobicity, and production of amyloid fibers and extracellular polymeric substances. The growth of dual-strain biofilms showed that five organisms formed biofilm with all 13 strains while seven formed no or only weak biofilm when cocultured. In dual-strain cultures, strains with different properties were able to complement each other, giving synergistic effects. Strongest biofilm formation was observed when a mixture of all 13 bacteria were grown together. These results on attachment and biofilm formation can serve as a tool for the design of tailored systems for the degradation of municipal and industrial wastewater.     

Biofilm formation by asymptomatic and virulent urinary tract infectious Escherichia coli strains

Escherichia coli is the most common organism associated with asymptomatic bacteriuria (ABU) in humans. In contrast to uropathogenic E. coli (UPEC) that cause symptomatic urinary tract infection, very little is known about the mechanisms by which these strains colonize the urinary tract. Here, we have investigated the biofilm-forming capacity on abiotic surfaces of groups of ABU strains and UPEC strains in human urine. We found that there is a strong bias; ABU strains were significantly better biofilm formers than UPEC strains. Our data suggest that biofilm formation in urinary tract infectious E. coli seems to be associated with ABU strains and appears to be an important strategy used by these strains for persistence in this high-flow environment.     

Phages of the marine cyanobacterial picophytoplankton

Cyanobacteria of the genera Synechococcus and Prochlorococcus dominate the prokaryotic component of the picophytoplankton in the oceans. It is still less than 10 years since the discovery of phages that infect marine Synechococcus and the beginning of the characterisation of these phages and assessment of their ecological impact. Estimations of the contribution of phages to Synechococcus mortality are highly variable, but there is clear evidence that phages exert a significant selection pressure on Synechococcus community structure. In turn, there are strong selection pressures on the phage community, in terms of both abundance and composition. This review focuses on the factors affecting the diversity of cyanophages in the marine environment, cyanophage interactions with their hosts, and the selective pressures in the marine environment that affect cyanophage evolutionary biology.     

Biofilm formation in plant-microbe associations

Bacteria adhere to environmental surfaces in multicellular assemblies described as biofilms. Plant-associated bacteria interact with host tissue surfaces during pathogenesis and symbiosis, and in commensal relationships. Observations of bacteria associated with plants increasingly reveal biofilm-type structures that vary from small clusters of cells to extensive biofilms. The surface properties of the plant tissue, nutrient and water availability, and the proclivities of the colonizing bacteria strongly influence the resulting biofilm structure. Recent studies highlight the importance of these structures in initiating and maintaining contact with the host by examining the extent to which biofilm formation is an intrinsic component of plant-microbe interactions.     

Biofilm formation in Streptococcus pneumoniae

Biofilm‐grown bacteria are refractory to antimicrobial agents and show an increased capacity to evade the host immune system. In recent years, studies have begun on biofilm formation by Streptococcus pneumoniae, an important human pathogen, using a variety of in vitro model systems. The bacterial cells in these biofilms are held together by an extracellular matrix composed of DNA, proteins and, possibly, polysaccharide(s). Although neither the precise nature of these proteins nor the composition of the putative polysaccharide(s) is clear, it is known that choline‐binding proteins are required for successful biofilm formation. Further, many genes appear to be involved, although the role of each appears to vary when biofilms are produced in batch or continuous culture. Prophylactic and therapeutic measures need to be developed to fight S. pneumoniae biofilm formation. However, much care needs to be taken when choosing strains for such studies because different S. pneumoniae isolates can show remarkable genomic differences. Multispecies and in vivo biofilm models must also be developed to provide a more complete understanding of biofilm formation and maintenance.     

Decolorization of azo dyes by marine Shewanella strains under saline conditions

Azo dye decolorization was studied with Shewanella strains under saline conditions. Growing cells of Shewanella algae and Shewanella marisflavi isolated from marine environments demonstrated better azo dye decolorization capacities than the other three strains from non-saline sources. Cell suspensions of S. algae and S. marisflavi could decolorize single or mixed azo dyes with different structures. Decolorization kinetics were described with Michaelis–Menton equation, which indicated better decolorization performance of S. algae over S. marisflavi. Lactate and formate were identified as efficient electron donors for amaranth decolorization by the two strains. S. algae and S. marisflavi could decolorize amaranth at up to 100 g?L^?1 NaCl or Na₂SO₄. However, extremely low concentration of NaNO₃ exerted strong inhibition on decolorization. Both strains could remove the color and COD of textile effluent during sequential anaerobic–aerobic incubation. Lower concentrations of NaCl (20–30 g?L^?1) stimulated the activities of azoreductase, laccase, and NADH-DCIP reductase. The decolorization intermediates were identified by high-performance liquid chromatography and Fourier transform infrared spectroscopy. Decolorization metabolites of amaranth were less toxic than original dye. These findings improved our knowledge of azo-dye-decolorizing Shewanella species and provided efficient candidates for the treatment of dye-polluted saline wastewaters.     

Biofilm formation by strains of Burkholderia cepacia complex in dependence of their phenotypic and genotypic characteristics

Biofilm formation was studied in 54 strains of Burkholderia cepacia complex isolated in 7 Moscow hospitals. 80% of strains (biofilm groups I and II) had the capacity to biofilm formation and only 16.7% of strains (group III) were not capable to biofilm formation. Molecular genetic methods allowed to identify one of the epidemic markers (CBL, IS hybrid sequence, Burkholderia Cepacia Epidemic Strain Marker - BCESM) in 46.7, 23.3, and 33.3% of strains from group I, II, and III respectively. Gene cepR from the Quorum Sensing system was identified in three biofilm groups in nearly equal frequency (92.3, 96.2 and 100% for group I, II, and III respectively), whereas cepl gene was found more often in group I (76.9%) and II (65.4%). Strains from all three groups had protease and lipase activity and 13.3% of group I strains had chitinolytic activity. B. cepacia strains from group I produced hemolysin in 33.3% of cases, from group II--in 26.6%, and from group III--in 11.1% of cases. The majority of Moscow hospital strains of B. cepacia complex were identified as B. cenocepacia (genomovar III, group A). RAPD-PCR method enabled to differentiate isolated strains into several genotypic variants. 13.3% of strains from group I were susceptible to imipenem/ciprofloxacin, as well as 33.3% of isolates from group II and 44.4% of isolates from group III.     

M13-based genotyping of marine cyanobacterial strains from the Indian subcontinent and maintained in the NFMC germplasm collection

The aim of this study was to analyze marine cyanobacterial culture collections strains of the Indian subcontinent at the level below species. This is important to improve the abilities of service culture collections to provide their user community with correctly identified and clean organisms. A total of 50 marine cyanobacterial strains were genotyped with M13 polymerase chain reaction (PCR) fingerprinting to provide diagnostic fingerprints for each culture. Depending on the strains, 9 to 26 bands were observed for the primer tested. Within the species, strains representing different isolates were genetically clearly different. Data obtained from genomic fingerprinting were used to construct binary distance matrix, and the neighbor-joining tree constructed demonstrated the ability of this method to differentiate strains at the intraspecific level. An important and useful result obtained in this study is the application of the M13 PCR fingerprinting method on almost all forms of cyanobacteria for strain and species discrimination.     

Biofilm formation by Acinetobacter baumannii strains isolated from urinary tract infection and urinary catheters

Systemic infections in avian species caused by avian pathogenic Escherichia coli (APEC) are economically devastating to poultry industries worldwide. To unravel factors possibly involved in APEC pathogenicity, suppression subtractive hybridization was applied, leading to the identification of a putative APEC autotransporter adhesin gene aatA in our previous study. In this study, pathogenic mechanism of AatA was further determined. A deletion mutant of aatA was constructed in the APEC DE205B, which results in the reduced capacity to adhere to DF-1 cells, defective virulence in vivo, and decreased colonization capacity in lung during the systemic infection compared with the wild-type strain. Furthermore, these capacities were restored in the complementation strains. These results indicated that AatA makes a significant contribution to APEC virulence through bacterial adherence to host tissues in vivo and in vitro. In addition, aggregation assays for strain AAEC189 expressing aatA indicated that AatA mediates cell aggregation and settling of cells. However, this cell aggregation is blocked by Type I fimbriae. This study illustrates the first examination of the role of AatA in aggregation and systemic infection.     

Biofilm formation and sloughing in Serratia marcescens are controlled by quorum sensing and nutrient cues

We describe here a role for quorum sensing in the detachment, or sloughing, of Serratia marcescens filamentous biofilms, and we show that nutrient conditions affect the biofilm morphotype. Under reduced carbon or nitrogen conditions, S. marcescens formed a classical biofilm consisting of microcolonies. The filamentous biofilm could be converted to a microcolony-type biofilm by switching the medium after establishment of the biofilm. Similarly, when initially grown as a microcolony biofilm, S. marcescens could be converted back to a filamentous biofilm by increasing the nutrient composition. Under high-nutrient conditions, an N-acyl homoserine lactone quorum-sensing mutant formed biofilms that were indistinguishable from the wild-type biofilms. Similarly, other quorum-sensing-dependent behaviors, such as swarming motility, could be rendered quorum sensing independent by manipulating the growth medium. Quorum sensing was also found to be involved in the sloughing of the filamentous biofilm. The biofilm formed by the bacterium consistently sloughed from the substratum after approximately 75 to 80 h of development. The quorum-sensing mutant, when supplemented with exogenous signal, formed a wild-type filamentous biofilm and sloughed at the same time as the wild type, and this was independent of surfactant production. When we removed the signal from the quorum-sensing mutant prior to the time of sloughing, the biofilm did not undergo significant detachment. Together, the data suggest that biofilm formation by S. marcescens is a dynamic process that is controlled by both nutrient cues and the quorum-sensing system.     

Biofilm formation in attached microalgal reactors

The objective of this study was to investigate the fundamental question of biofilm formation. First, a drum biofilm reactor was introduced. The drums were coated with three porous substrates (cotton rope, canvas, and spandex), respectively. The relationships among the substrate, extracellular polymeric substances (EPS), and adhesion ratio were analyzed. Second, a plate biofilm reactor (PBR) was applied by replacing the drum with multiple parallel vertical plates to increase the surface area. The plates were coated with porous substrates on each side, and the nutrients were delivered to the cells by diffusion. The influence of nitrogen source and concentration on compositions of EPS and biofilm formation was analyzed using PBR under sunlight. The results indicated that both substrate and nitrogen were critical on the EPS compositions and biofilm formation. Under the optimal condition (glycine with concentration of 1 g l^?1 and substrate of canvas), the maximum biofilm productivity of 54.46 g m^?2 d^?1 with adhesion ratio of 84.4 % was achieved.     

Biofilm formation in water cooling systems

Biofilm formation on stainless steel samples immersed in cooling water has been evaluated by exposing metal samples to cooling seawater for 30 days. Anaerobic bacteria were then at 1.6 × 10⁶/cm², with sulphate-reducing species predominating. Aerobic bacteria and fungi were 2600 and 140/cm², respectively. After 60 days, numbers of aerobic microorganisms remained constant whereas the count of anaerobic microorganisms had increased to 1.8×10⁹/cm². Scanning electron microscopy showed the presence of morphologically different microorganisms in deposits and as a mucilaginous net. No signs of corrosion were detected on the stainless steel surface.The authors are with the Departamento de Engenharia Bioquimica Centro de Tecnologia, Bloco E. Universidade Federal do Rio de Janeiro Ilha do Fundão, 21941-900 Rio de Janeiro, Brazil