Potential of mechanical cleaning of membranes from a mebrane bioreactor
Brink, P. van den; Vergeldt, F.J. ; As, H. van; Zwijnenburg, A. ; Temmink, H. - \ 2013
Journal of Membrane Science 429 (2013). - ISSN 0376-7388 - p. 259 - 267.
drinking-water - biofilm reactor - critical flux - waste-water - exopolysaccharides - denitrification - precipitation - communities - limitation - bacteria
Several membrane fouling mechanisms have been identified in membrane bioreactors. While cake layers can be removed by physical cleaning, irreversible fouling such as a gel layer is difficult to remove by physical cleaning during filtration. Harsh mechanical cleaning was applied in this study to evaluate how much fouling could be maximally removed and distribution of remaining fouling was investigated. The fouling resistance of several membranes operated at different relatively low fluxes was followed during long term continuous flux operation. Remaining fouling was observed with scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Dead-end filtration tests with mechanically cleaned membranes showed a decreased permeability. To determine whether bacteria were present in the remaining fouling, oxygen consumption was quantified. Even after harsh mechanical cleaning, membrane samples showed considerable oxygen consumption. SEM did not show fouling inside the membrane. Of several membranes operated for at least 1 year, the permeate side was covered with bacteria and extracellular polymeric substances (EPS). These results show that fouling cannot be removed completely by harsh mechanical cleaning and that both feed and permeate side of the membrane contains biofouling. This fouling on the permeate side should not be neglected when designing membrane cleaning.
Histological examination of horse chestnut infection by Pseudomonas syringae pv aesculi and non-destructive heat treatment to stop disease progression
Keijzer, J. de; Broek, L.A.M. van den; Ketelaar, T. ; Lammeren, A.A.M. van - \ 2012
PLoS ONE 7 (2012). - ISSN 1932-6203 - 12 p.
alginate production - bacterial polysaccharides - suberin deposition - bleeding canker - fire blight - tree bark - virulence - lignin - leaves - exopolysaccharides
Since its emergence in Northwest Europe as a pathogen that infects trunks and branches of Aesculus spp. (the horse chestnuts) approximately one decade ago, Pseudomonas syringae pv. aesculi has rapidly established itself as major threat to these trees. Infected trees exhibit extensive necrosis of phloem and cambium, which can ultimately lead to dieback. The events after host entry leading to extensive necrosis are not well documented. In this work, the histopathology of this interaction is investigated and heat-treatment is explored as method to eradicate bacteria associated with established infections. The early wound-repair responses of A. hippocastanum, both in absence and presence of P. s. pv. aesculi, included cell wall lignification by a distinct layer of phloem and cortex parenchyma cells. The same cells also deposited suberin lamellae later on, suggesting this layer functions in compartmentalizing healthy from disrupted tissues. However, monitoring bacterial ingress, its construction appeared inadequate to constrain pathogen spread. Microscopic evaluation of bacterial dispersal in situ using immunolabelling and GFP-tagging of P. s. pv. aesculi, revealed two discriminative types of bacterial colonization. The forefront of lesions was found to contain densely packed bacteria, while necrotic areas housed bacterial aggregates with scattered individuals embedded in an extracellular matrix of bacterial origin containing alginate. The endophytic localization and ability of P. s. pv aesculi to create a protective matrix render it poorly accessible for control agents. To circumvent this, a method based on selective bacterial lethality at 39 °C was conceived and successfully tested on A. hippocastanum saplings, providing proof of concept for controlling this disease by heat-treatment. This may be applicable for curing other tree cankers, caused by related phytopathogens
Heterologous expression of the pneumococcal serotype 14 polysaccharide in Lactococcus lactis requires lactococcal epsABC regulatory genes
Nierop Groot, M.N. ; Godefrooij, J. ; Kleerebezem, M. - \ 2008
Applied and Environmental Microbiology 74 (2008)3. - ISSN 0099-2240 - p. 912 - 915.
streptococcus-pneumoniae - capsular polysaccharide - cell-wall - exopolysaccharides - length - cpsd
The pneumococcal serotype 14 polysaccharide was produced in Lactococcus lactis by coexpressing pneumococcal polysaccharide type 14-specific genes (cpsFGHIJKL(14)) with the lactococcal regulatory and priming glucosyltransferase-encoding genes specific for B40 polysaccharide (epsABCD(B40)). The polysaccharide produced by Lactococcus was secreted in the medium, simplifying downstream processing and polysaccharide isolation from culture broth