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This investigation is focused on the combined effect of bacterial physicochemical characteristics and motility on cell adhesion and deposition using a flow-through quartz crystal microbalance with dissipation (QCM-D). Three model flagellated strains with different degrees of motility were selected, including a highly motile Escherichia coli K12 MG1655, an environmental strain Sphingomonas wittichii RW1, and a nonmotile (with paralyzed flagella) Escherichia coli K12 MG1655 ΔmotA that is incapable of encoding the motor torque generator for flagellar movement. Of the three strains, S. wittichii RW1 is highly hydrophobic, while E. coli strains are equally hydrophilic. Consideration of the hydrophobicity provides an alternative explanation for the bacterial adhesion behavior. QCM-D results show that motility is a critical factor in determining bacterial adhesion, as long as the aquatic chemical conditions are conducive for motility and the substratum and bacterial surface are similarly hydrophobic or hydrophilic. Once their properties are not similar, the contribution of hydrophobic interactions becomes more pronounced. QCM-D results suggest that during adhesion of the hydrophobic bacterium, S. wittichii RW1, the initial step of adhesion and maturation of bacteria-substratum interaction on hydrophilic surface includes a dynamic change of the viscoelastic properties of the bond bacterium-surface becoming more viscously oriented.

A parasitic chytrid that attacks the green alga Haematococcus pluvialis was recently isolated in our laboratory and identified as a novel species from the phylum Blastocladiomycota, named herein Paraphysoderma sedebokerensis (nom. prov.). A method for early and precise detection of chytrid infections was developed using the fluorescent dye, Nile red, which stained the chytrids' sporangia. Using this technique we determined the specificity of Paraphysoderma sedebokerensis for 13 algal species belonging to the Chlorophyta. Algal species tested including: Chlamydomonas nivalis, Chlorella emersonii, Chlorella vulgaris, Chlorococcum sp., Chlorogonium elongatum, Monoraphidium braunii, Muriella zofigiensis, Scenedesmus obliquus, Scenedesmus vacuolatus (two strains), and Scotiellopsis oocystiformis were either resistant to infection, or only experienced slight levels of infection during exponential growth. During exponential growth phase 100% Chlorella zofigiensis Donz cells were infected, but none developed any infection during resting stage. Only in cultures of H. pluvialis did infections develop rapidly (3-4 days) and intensively (100% cells infected) during both the logarithmic and stationary stages of growth. We suggest that the newly isolated chytrid, Paraphysoderma sedebokerensis (nom. prov.), is highly specific for H. pluvialis, but has a limited capacity to infect other green algae.

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In the present study, we investigate the possible contribution of Sphingomonas spp. glycosphingolipids (GSL) and its extracellular polymeric substances (EPS) to the initial colonization and development of biofilm bodies on reverse osmosis (RO) membranes. A combination of an RO cross-flow membrane lab unit, a quartz crystal microbalance with dissipation (QCM-D), and a rear stagnation point flow (RSPF) system with either model bacteria (Sphingomonas wittichii, Escherichia coli, and Pseudomonas aeruginosa) or vesicles made of the bacterial GSL or LPS was used. Results showed noticeable differences in the adhesion LPS versus GSL vesicles in the QCM-D, with the latter exhibiting 50% higher adhesion to polyamide coated crystals (mimicking an RO membrane surface). A similar trend was observed for EPS extracted from S. wittichii, when compared to the adhesion tendency of EPS extracted from P. aeruginosa. By applying the whole-cell approach in the RO lab unit, the cumulative impact of S. wittichii cells composing GSL and probably their EPS reduced the permeate flux during bacterial accumulation on the membrane surface. Experiments were conducted with the same amount of Sphingomonas spp. or Escherichia coli cells resulting in a two times greater flux decline in the presence of S. wittichii. The distinct effects of Sphingomonas spp. on RO membrane biofouling are likely a combination of GSL presence (known for enhancing adhesion when compared to non-GSL containing bacteria) and the EPS contributing to the overall strength of the biofilm matrix.