Combinatorial materials research applied to the development of new surface coatings XVI: fouling-release properties of amphiphilic polysiloxane coatings

High-throughput methods were used to prepare and characterize the fouling-release (FR) properties of an array of amphiphilic polysiloxane-based coatings possessing systematic variations in composition. The coatings were derived from a silanol-terminated polydimethylsiloxane, a silanol-terminated polytrifluorpropylmethylsiloxane (CF3-PDMS), 2-[methoxy(polyethyleneoxy)propyl]-trimethoxysilane (TMS-PEG), methyltriacetoxysilane and hexamethyldisilazane-treated fumed silica. The variables investigated were the concentration of TMS-PEG and the concentration of CF3-PDMS. In general, it was found that the TMS-PEG and the CF3-PDMS had a synergist effect on FR properties with these properties being enhanced by combining both compounds into the coating formulations. In addition, reattached adult barnacles removed from coatings possessing both TMS-PEG and relatively high levels of CF3-PDMS displayed atypical base-plate morphologies. The majority of the barnacles removed from these coatings exhibited a cupped or domed base-plate as compared to the flat base-plate observed for the control coating that did not contain TMS-PEG or CF3-PDMS. Coating surface analysis using water contact angle measurements indicated that the presence of CF3-PDMS facilitated migration of TMS-PEG to the coating/air interface during the film formation/curing process. In general, coatings containing both TMS-PEG and relatively high levels of CF3-PDMS possessed excellent FR properties.

The uronic acids assay: a method for the determination of chemical activity on biofilm EPS

In this work, the uronic acids assay was evaluated for its potential to function as a bioassay to screen for antagonistic activity against the production of microbial biofilm exopolysaccharide (EPS). The assay was first applied to biofilms produced in the presence of two universal disinfectants (sodium hypochlorite and sodium dodecyl sulfate) known to inhibit microbial growth and biofilm formation. The performance of the assay was then characterized through statistical assessment of threshold concentrations for disinfection efficiency and consistency relative to values reported in the literature. The assay was then evaluated for its utility in screening for enzymatic or chemical inhibitors of biofilm formation (eg glycosidases, halogenated furanones, and semi-crude fractions extracted from minimally fouled marine plants) and its ability to distinguish between true anti-biofilm activity and simple disinfection. Activity was characterized as (i) no effect, (ii) a true positive effect (ie increased biofilm EPS), (iii) anti-bacterial activity (ie decreased biofilm EPS and analogous decrease in planktonic growth), and (iv) anti-biofilm EPS activity (ie decreased biofilm EPS, without analogous decrease in planktonic growth). Results demonstrate that the uronic acids assay can augment existing biofilm characterization methods by providing a quantitative measure of biofilm EPS.

Combinatorial materials research applied to the development of new surface coatings IV. A high-throughput bacterial biofilm retention and retraction assay for screening fouling-release performance of coatings

A high-throughput bacterial biofilm retention screening method has been augmented to facilitate the rapid analysis and down-selection of fouling-release coatings for identification of promising candidates. Coatings were cast in modified 24-well tissue culture plates and inoculated with the marine bacterium Cytophaga lytica for attachment and biofilm growth. Biofilms retained after rinsing with deionised water were dried at ambient laboratory conditions. During the drying process, retained biofilms retracted through a surface de-wetting phenomenon on the hydrophobic silicone surfaces. The retracted biofilms were stained with crystal violet, imaged, and analysed for percentage coverage. Two sets of experimental fouling-release coatings were analysed with the high-throughput biofilm retention and retraction assay (HTBRRA). The first set consisted of a series of model polysiloxane coatings that were systematically varied with respect to ratios of low and high MW silanol-terminated PDMS, level of cross-linker, and amount of silicone oil. The second set consisted of cross-linked PDMS-polyurethane coatings varied with respect to the MW of the PDMS and end group functionality. For the model polysiloxane coatings, HTBRRA results were compared to data obtained from field immersion testing at the Indian River Lagoon at the Florida Institute of Technology. The percentage coverage calculations of retracted biofilms correlated well to barnacle adhesion strength in the field (R(2)=0.82) and accurately identified the best and poorest performing coating compositions. For the cross-linked PDMS-polyurethane coatings, the HTBRRA results were compared to combinatorial pseudobarnacle pull-off adhesion data and good agreement in performance was observed. Details of the developed assay and its implications in the rapid discovery of new fouling-release coatings are discussed.

Peptidoglycan from Bacillus cereus mediates commensalism with rhizosphere bacteria from the Cytophaga-Flavobacterium group

Previous research in our laboratory revealed that the introduction of Bacillus cereus UW85 can increase the populations of bacteria from the Cytophaga-Flavobacterium (CF) group of the Bacteroidetes phylum in the soybean rhizosphere, suggesting that these rhizosphere microorganisms have a beneficial relationship (G. S. Gilbert, J. L. Parke, M. K. Clayton, and J. Handelsman, Ecology 74:840-854, 1993). In the present study, we determined the frequency at which CF bacteria coisolated with B. cereus strains from the soybean rhizosphere and the mechanism by which B. cereus stimulates the growth of CF rhizosphere strains in root exudate media. In three consecutive years of sampling, CF strains predominated among coisolates obtained with B. cereus isolates from field-grown soybean roots. In root exudate media, the presence of B. cereus was required for CF coisolate strains to reach high population density. However, rhizosphere isolates from the phylum Proteobacteria grew equally well in the presence and absence of B. cereus, and the presence of CF coisolates did not affect the growth of B. cereus. Peptidoglycan isolated from B. cereus cultures stimulated growth of the CF rhizosphere bacterium Flavobacterium johnsoniae, although culture supernatant from B. cereus grown in root exudate media did not. These results suggest B. cereus and CF rhizosphere bacteria have a commensal relationship in which peptidoglycan produced by B. cereus stimulates the growth of CF bacteria.

In vitro cultivation and antibiotic susceptibility of a Cytophaga-like intracellular symbiote isolated from the tick Ixodes scapularis

A Cytophaga-like organism (CLO), isolated from the tick Ixodes scapularis (IsCLO), was adapted to growth in insect cell lines and its antibiotic sensitivity was tested. IsCLO were introduced to four insect cell lines, and their growth was measured by quantitative polymerase chain reaction. IsCLO propagated well in a mosquito cell line, AeAl-2, and caused cytopathic effects in host cells. A lepidopteran cell line, HZ-AM1, was also suitable for propagation of IsCLO and kept a steady state with bacterial growth. Using IsCLO-infected AeAl-2, antibiotics effective against the bacteria included ampicillin, chloramphenicol, penicillin-G, rifampicin, and tetracycline. These antibiotics will be useful for eliminating CLO from host arthropods, which is necessary for in vivo studies of the intracellular facultative symbiotes.

Zobellia galactanovorans gen. nov., sp. nov., a marine species of Flavobacteriaceae isolated from a red alga, and classification of [Cytophaga] uliginosa (ZoBell and Upham 1944) Reichenbach 1989 as Zobellia uliginosa gen. nov., comb. nov

A mesophilic, aerobic, non-flagellated, gliding bacterium, forming yellow colonies and designated DsijT, was isolated from a red alga on the sea-shore of Roscoff, Brittany, France. DsijT was selected for its ability to actively degrade both agars and carrageenans. The Gram-negative cells occurred singly or in pairs as long rods. The temperature range for growth was 13-45 degrees C, with an optimum at 35 degrees C. The pH range for growth at 35 degrees C was from 6.0 to 8.5, with an optimum around pH 7.0. The NaCl concentrations required for growth at 35 degrees C and pH 7.0 ranged from 5 to 60 g l(-1), with an optimum around 25 g l(-1). The G+C content of the genomic DNA was 42-43 mol%. Phylogenetic analysis of 16S rRNA gene sequences indicated that strain DsijT is closely related to [Cytophaga] uliginosa DSM 2061T. Phenotypic features, however, allowed DsijT and [Cytophaga] uliginosa strains to be distinguished on the basis of ten traits (spreading behaviour, assimilation of eight compounds and amylase production). Their total protein profiles were also different and DNA-DNA hybridization experiments confirmed that DsijT constitutes a new species, distinct from [Cytophaga] uliginosa. Based on the phenotypic features and the phylogenetic relationships of the Flavobacteriaceae, a new genus designated Zobellia gen. nov. is proposed to include Zobellia galactanovorans gen. nov., sp. nov., while [Cytophaga] uliginosa becomes Zobellia uliginosa comb. nov. The type strain of Zobellia galactanovorans is DsijT (= DSM 12802T = CIP 106680T).

Acetate acts as a protonophore and differentially affects bead movement and cell migration of the gliding bacterium Cytophaga johnsonae (Flavobacterium johnsoniae)

Cells of Cytophaga johnsonae (now Flavobacterium johnsoniae) are able to translocate on solid surfaces but are unable to swim in liquid media. Organelles that may be involved in this gliding motility have not been detected, and the mechanism(s) responsible remains unknown. The movement of latex beads attached to the cell surface is considered by some to be a manifestation of the gliding machinery. In this study, acetate (in nutrient-level quantity, 45 mM) was found to inhibit bead movement on cell surfaces, whilst formation and movement of groups of cells (rafts) and typical colony spread were not affected; generation time (in liquid culture) was only slightly increased. Since acetate is a weak acid and is recognized as a protonophore, various electron-transport-associated features were assessed in an effort to understand the differential effects of acetate on bead movement and cell motility. Selected protonophores and electron transport inhibitors were tested to compare their effects on cell translocation and metabolic activities with those of acetate. Although O2 consumption was not significantly affected in the presence of acetate and the protonmotive force decreased only minimally, ATP levels were markedly decreased. Arsenate and cyanide were also shown to inhibit bead movement but did not inhibit either movement of rafts of cells or colony spreading. Cyanide lowered O2 consumption, while arsenate did not; both compounds effected substantial decreases in cellular ATP content, but little or no decrease in protonmotive force. The inhibitory effects of these compounds on bead movement over cell surfaces contrasted with the continued ability of cells to form rafts, to glide and to form spreading colonies and led to the conclusion that bead movement is not a complete correlate of the gliding machinery of C. johnsonae. In addition, it seems likely that bead movement is more affected by the level of cellular ATP than it is by the protonmotive force, which has been assumed to provide the energy (derived from the transmembrane gradients) for the gliding machinery.

Negative chemotaxis in Cytophaga johnsonae

Chemotaxis, both positive and negative, has been extensively studied in flagellated bacteria, such as Escherichia coli and Salmonella typhimurium, but not in gliding bacteria. The rapidly motile gliding bacterium Cytophaga johnsonae has been seen to be repelled by H2O2, OCl-, and N-chlorotaurine, as well as by low pH. Its response to H2O2 was eliminated by catalase. Nalidixic acid at 200 microM, which inhibits the growth but not the motility of C. johnsonae, did not interfere with its negative chemotactic response to H2O2, whereas sodium phosphate at 10 mM, which inhibits motility, did so. Cytophaga johnsonae was not repelled by taurine, n-octanol, phenol, L-valine, or high pH. Chemotaxis can be conveniently studied in gliding bacteria such as C. johnsonae.

Temporal sequence of the recovery of traits during phenotypic curing of a Cytophaga johnsonae motility mutant

The lack of cell translocation and the resulting formation of nonspreading colonies of mutants of the gram-negative gliding bacterium Cytophaga johnsonae have been correlated with the loss of cell surface features of the organism. These cell surface traits include the ability to move polystyrene-latex beads over the cell surface and the ability to be infected by bacteriophages that infect the parent strain. In order to assess whether these traits reflect structures or functions that actually play a role in gliding, we studied a mutant (21A2I) selected for its inability to form spreading colonies; it is deficient in sulfonolipid, lacks bead movement ability, and is resistant to at least one bacteriophage. The provision of cysteate (a specific sulfonolipid precursor) restores lipid content and gliding to the mutant; hence, the lipids are necessary for motility. Growth with cysteate also restores bead movement and phage sensitivity. In order to determine the temporal relationship of these traits, we undertook a kinetic study of the appearance of them after addition of cysteate to the mutant. One predicts that appearance of a trait essential for cell translocation will either precede or accompany the appearance of this ability, while a nonessential trait need not do so. Sulfonolipid synthesis was the only trait that appeared before gliding; this is consistent with its established importance for motility. Bead movement and phage sensitivity first appeared only after gliding started, suggesting that the machinery involved in those processes is not necessary, at least for the initiation of gliding.

Evidence for the participation of N-acetylated amino sugars in the coaggregation between Cytophaga species strain DR2001 and Actinomyces israelii PK16

Coaggregation between Cytophaga sp. strain DR2001 and Actinomyces israelii PK16 was partially inhibited by certain N-acetylated amino sugars (N-acetylneuraminic acid, N-acetylgalactosamine, and N-acetylglucosamine) and was completely inhibited by the trisaccharide neuraminin-lactose. The monosaccharides exerted their effect at concentrations between 30 to 100 mM, whereas the trisaccharide was an effective inhibitor at significantly lower concentrations. Outer membrane preparations caused A. israelii PK16 cells to aggregate; however, vesicles released from the cell envelope during growth failed to do so. Adherence studies with a non-coaggregating mutant of the cytophaga suggest that the spheroidal hydroxyapatite attachment sites and coaggregation receptors are separate entities.

Increased extracellular production of a cholinesterase-solubilising factor by Cytophaga NCMB 1314 during magnesium starvation

A Cytophaga sp. with the property of liberating a cholinesterase which is found in body muscle of plaice was studied. The liberation was caused by a factor of which more than 90% was found outside the bacterial cell and might possibly be associated within the slime material surrounding the bacteria. Magnesium limitation during growth of Cytophaga sp. in batch cultures resulted in an about 10-fold increase in extracellular factor activity. The increase could be immediately stopped by addition of magnesium ions or chloramphenicol to the medium. The effect of the latter might indicate that the increase in factor activity is dependent on protein synthesis under magnesium-limiting conditions.

Sensitivity of cellulolytic bacteria to antibiotics

The sensitivity of eight cellulolytic bacterial strains to eight antibiotics was tested. The results showed that, in general, the strains belonging to Cytophaga, Cellvibrio, and Cellfalcicula are more sensitive to antibiotics than those strains that belong to Sporocytophaga and Cellulomonas. The inhibitory activity of the tested antibiotics, though differing with different strains, showed the following categories: tetracycline, erythromycin, and chloromycetin were most active, kanamycin, streptomycin, and neomycin were intermediate, while novobiocin and penicillin showed low activity.

Surface structure of gliding bacteria after freeze-etching

Ultrastructural studies of gliding bacteria demonstrate 10- to 11-nm beads on the inner surface of the outer bilayer of Cytophaga columnaris. These were not found in Myxococcus xanthus. On treatment with glutaraldehyde and ethanol, the beads appear in linear arrays.

The isolation and enumeration of cytophagas

A comparison of 20 media based on degraded milk protein or tryptone, yeast extract, and sodium acetate snowed that various new formulae were superior to standard media for enumeration of cytophagas from aquatic habitats, for their isolation, and for maximum expression of the spreading characteristic. The use of 0.1 μliter/liter Tween 20 in dilution blanks increased counts of cytophagas up to threefold, but incorporation of Tween 20 into the plating agar had no significant effect on the numbers recovered. Sodium lauryl sulfate (S.L.S.) was examined as a possible screening agent for identification of cytophagas. A concentration of 0.1% S.L.S. inhibited the growth of 97% of the 66 cytophagas tested, but more than 80% of the other 41 organisms tested were also affected. However, 91% of the cytophagas were sensitive to S.L.S. and showed proteolysis on skim acetate medium compared to 53% of the Flavo-bacteria and 50% of the other organisms tested. None of the third group of organisms could be confused morphologically with the cytophaga group; thus it is suggested that S.L.S. susceptibility performed on skim acetate medium could be a useful screening test for cytophagas.