Heidi Schraft’s research while affiliated with Lakehead University and other places

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Publications (33)


Structure of cake layer in a submerged anaerobic membrane bioreactor
  • Article

May 2011

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192 Reads

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151 Citations

Journal of Membrane Science

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A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) was used for thermomechanical pulping whitewater treatment. Sludge cake formation on membrane surfaces was identified as the dominant mechanism of membrane fouling. The spatial distribution of physical, chemical and microbiological structure of cake layers was characterized by various analytical techniques, including micro-tome slicing technique, confocal laser scanning microscopy (CLSM), conventional optical microscopy (COM), scanning electron microscopy (SEM)-energy-dispersive X-ray analyzer (EDX), particle size distribution (PSD) analysis, Fourier transform infrared (FTIR) spectroscopy, extraction and chemical analysis of extracellular polymeric substances (EPS), and polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). The results showed that the areal porosity decreased from the top layer to the bottom layer. Smaller flocs had a higher tendency to accumulate on membrane surfaces but the consolidation of cake sludge in the bottom layers resulted in larger flocs as compared to the fresh cake sludge formed on the top layers. There was an increase in the bound EPS density (mg EPS/cm(3) wet sludge) and a decrease in the ratio of proteins to polysaccharides in bound EPS from the top to bottom layers. PCR-DGGE study showed that there were significant differences in microbial community population density along the cake layer depth. Through the CLSM and COM images, cake layer was found to have a loose outer surface when compared with the cake bottom. The results provide a new insight in cake layer structure and suggest that structures change significantly from the top layer to the bottom layer.


Electrochemical and microbiological characterization of paper mill biofilms

October 2010

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22 Reads

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11 Citations

Biofouling

Biofilm samples collected from inside and outside the press and former sections of paper machines in a Northwestern Ontario paper mill for a period of 2 years were characterized microbiologically and electrochemically. Bacterial community profiling was done using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and selected bacterial isolates were identified using 16S rDNA analysis. The bacterial community showed the presence of Proteobacteria, Firmicutes, and Actinobacteria. Sphingomonas sp. was found to be the most common bacterial species, which showed the highest production of extracellular polymeric substances. Bacteria isolated from biofilms showed better adhesion properties than those from water samples. Cyclic voltammetry and electrochemical impedance spectroscopy studies showed that bacteria isolated from biofilms and feed water collected from inside the machine were more easily oxidized than those from outside, suggesting the need for a more rigorous biofilm abatement strategy for inside paper machines.


Figure 1. Schematic diagram of lignin degradation by basidiomycetes white-rot fungi: the major steps and enzymes involved (refer to text). 
Table 1 . The features of the main two groups of fungal ligninolytic enzymes
Table 2 . Mechanisms and enzymes involved in the production of • OH in different fungi
Fungal biodegradation and enzymatic modification of lignin
  • Article
  • Full-text available

May 2010

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3,250 Reads

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622 Citations

International Journal of Biochemistry and Molecular Biology

Lignin, the most abundant aromatic biopolymer on Earth, is extremely recalcitrant to degradation. By linking to both hemicellulose and cellulose, it creates a barrier to any solutions or enzymes and prevents the penetration of lignocellulolytic enzymes into the interior lignocellulosic structure. Some basidiomycetes white-rot fungi are able to degrade lignin efficiently using a combination of extracellular ligninolytic enzymes, organic acids, mediators and accessory enzymes. This review describes ligninolytic enzyme families produced by these fungi that are involved in wood decay processes, their molecular structures, biochemical properties and the mechanisms of action which render them attractive candidates in biotechnological applications. These enzymes include phenol oxidase (laccase) and heme peroxidases [lignin peroxidase (LiP), manganese peroxidase (MnP) and versatile peroxidase (VP)]. Accessory enzymes such as H(2)O(2)-generating oxidases and degradation mechanisms of plant cell-wall components in a non-enzymatic manner by production of free hydroxyl radicals (·OH) are also discussed.

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A novel selective growth medium-PCR assay to isolate and detect

March 2010

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106 Reads

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47 Citations

Journal of Microbiological Methods

Sphingomonas species can be found ubiquitously in the environment and can be frequently found in surface biofilms. Some Sphingomonas strains are well known for metabolizing complex organic pollutants but some are opportunistic human pathogens. Despite the importance of the Sphingomonas species, a reliable system to isolate this group of bacteria from the environment has not been developed. In this study, a combined streptomycin-piperacillin selective growth medium/polymerase chain reaction (PCR) detection approach is developed to isolate and identify the Sphingomonas bacteria. A total of 72 known Sphingomonas strains (including 21 different Sphingomonas species type strains) and 14 non-Sphingomonas species were tested using a new Sphingomonas-specific growth medium containing 100 and 50 microg/ml streptomycin and piperacillin, respectively. All the Sphingomonas strains showed positive growth on the selective medium and no growth was shown by the non-Sphingomonas species. In addition, two sets of PCR primers targeting the serine palmitoyltransferase gene (spt), a crucial sphingolipid biosynthesis gene, were developed. With the exception of the Sphingomonas subarctica type strain, 71 of the 72 known Sphingomonas samples were amplified positively by either one or both of the spt-specific primers. None of the non-Sphingomonas bacteria were amplified by the spt primers. To verify the effectiveness of this novel approach for use in environmental screening applications the Sphingomonas selective medium was used to isolate 165 potential Sphingomonas isolates, including 101 yellow, 4 orange and 58 unpigmented isolates, from the influent water and biofilm samples of a pulp and paper mill in Northwestern Ontario. Screening of these isolates with the two Sphingomonas spt-PCR primer sets showed that 98% of the yellow isolates and 100% of the orange isolates were positive to the spt-PCR test. None of the unpigmented isolates was positive to the spt-PCR assay. The 16S rDNA of 17% of the spt+ve and -ve isolates were sequenced and analyzed. All of the yellow and orange pigmented isolates were Sphingomonas while none of the unpigmented isolates were Sphingomonas. REP-PCR was performed on 79 Sphingomonas samples randomly selected from the paper mill and hospital isolates and showed that a diverse group of Sphingomonas can be grown or isolated by our Sphingomonas selective growth medium. Therefore, by using the streptomycin-piperacillin selective growth medium in combination with the colour pigmentation and the positive spt-PCR reactions of the isolates, a diverse population of Sphingomonas strains can be isolated and identified from complex microbial communities with high accuracy.


Some of the lignocellulosic residues produced by different industries and potential for ethanol production 
Examples of different fungi producing different lignocellulolytic enzymes and their substrates. 
Overview of the three groups of fungal cellulolytic enzymes and their main features. 
Fungal Bioconversion of Lignocellulosic Residues; Opportunities & Perspectives

September 2009

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1,309 Reads

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783 Citations

International Journal of Biological Sciences

The development of alternative energy technology is critically important because of the rising prices of crude oil, security issues regarding the oil supply, and environmental issues such as global warming and air pollution. Bioconversion of biomass has significant advantages over other alternative energy strategies because biomass is the most abundant and also the most renewable biomaterial on our planet. Bioconversion of lignocellulosic residues is initiated primarily by microorganisms such as fungi and bacteria which are capable of degrading lignocellulolytic materials. Fungi such as Trichoderma reesei and Aspergillus niger produce large amounts of extracellular cellulolytic enzymes, whereas bacterial and a few anaerobic fungal strains mostly produce cellulolytic enzymes in a complex called cellulosome, which is associated with the cell wall. In filamentous fungi, cellulolytic enzymes including endoglucanases, cellobiohydrolases (exoglucanases) and beta-glucosidases work efficiently on cellulolytic residues in a synergistic manner. In addition to cellulolytic/hemicellulolytic activities, higher fungi such as basidiomycetes (e.g. Phanerochaete chrysosporium) have unique oxidative systems which together with ligninolytic enzymes are responsible for lignocellulose degradation. This review gives an overview of different fungal lignocellulolytic enzymatic systems including extracellular and cellulosome-associated in aerobic and anaerobic fungi, respectively. In addition, oxidative lignocellulose-degradation mechanisms of higher fungi are discussed. Moreover, this paper reviews the current status of the technology for bioconversion of biomass by fungi, with focus on mutagenesis, co-culturing and heterologous gene expression attempts to improve fungal lignocellulolytic activities to create robust fungal strains.


Paper mill biofilms: A comprehensive study

January 2009

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34 Reads

Biofilms collected from a paper mill in Northwestern Ontario were characterized with respect to physical, chemical, microbiological and electrochemical properties. Biofilm samples were collected from inside and outside of the paper machines during extended periods of maintenance shutdown and were analysed for properties such as pH, texture, total culturable bacterial counts, bacterial community structure, adhesion studies using biofilm bacterial isolates and adsorption and desorption properties using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Water samples collected at the same sampling points were also analysed for pH, temperature and total culturable microbial load. The results showed a higher bacterial count (105 -108 cfu/ml) in biofilms than in the water samples (102 -106 cfu/ml). The pH of biofilms collected from the inside surfaces of paper machines was lower (2.9-5.5) than that from the outside surfaces (6.4-6.9). The bacterial community structure studied using nucleic acid finger printing (DGGE) techniques and 16S rDNA profiling revealed the presence of several groups of bacteria; Proteobacteria, firmicutes and actinobacteria. Sphingomonas sp. was found to be the most common bacterial species that also produced the highest volume of extracellular polymeric substances. Biofilm formation assay using bacterial isolates showed the presence of good and weak biofilm formers. Finally, the cyclic voltammetry studies showed that biofilms from inside the machine and the bacteria isolated from inside water were easier to oxidize than those from outside the machine and outside water samples.


Chromosomal gfp labelling of Pseudomonas aeruginosa using a mini-Tn7 transposon: application for studies of bacteriahost interactions

January 2008

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111 Reads

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13 Citations

Analysis of bacterial interactions with host cells using multiple techniques is essential for studies on microbial pathogenesis and for the development of new antimicrobial therapies. Pseudomonas aeruginosa is an important opportunistic pathogen that can cause severe, often life-threatening pulmonary infections in individuals with impaired host defense mechanisms. Using a mini-Tn7 transposon delivery system, we have chromosomally labelled the strain P.aeruginosa PAK with a green fluorescent protein gene (gfp) and tested PAKgfp as a research tool for studies of bacteriahost interactions. We were able to reliably and rapidly measure the interactions of PAKgfp with A549 human lung epithelial cells by using flow cytometry, a fluorometric microplate reader-based assay, and fluorescence microscopy. With these analytical tools, we have demonstrated the adhesion of PAKgfp to the extracellular matrix protein fibronectin and the involvement of fibronectin in PAKgfpA549 cell interactions. PAKgfp can be successfully used to explore the effects of various pharmacological compounds on P.aeruginosa host cell interactions in both in vitro and in vivo systems, with potentially important medical applications.


A Diffusion-Reaction Model of a Mixed-Culture Biofilm Arising in Food Safety Studies

January 2008

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29 Reads

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13 Citations

Bacterial biofilms are communities of microorganisms that develop on interfaces in aqueous environments. We formulate a density-dependent diffusion-reaction model for the growth of a dual-species biofilm. Both bacteria respond differently to their environment and develop different types of biofilms: One is a classical aerobic biofilm former that produces the characteristic cluster-and-channel biofilm morphology, the other one also develops under anaerobic conditions and tends to form flat, creeping biofilms. A previously developed nonstandard finite-difference scheme is adapted for the computer simulation. In a numerical experiment it is shown how variations of a single parameter (growth rate) can trigger different spatial structure and organisation of the biofilm community.


Direct growth of biofilms on an electrode surface and its application in electrochemical biosensoring

December 2007

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52 Reads

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20 Citations

Journal of Electroanalytical Chemistry

In this study, a Sphingomonas Strain 264 isolated from pulp and paper biofilms was used for electrochemical studies towards applications in biosensor development based on its high ability to produce extracellular polymeric substances (EPS), along with its rapid growth and tendency to flocculate. The Strain 264 biofilm was directly grown on an Au thin film and was studied with a combination of optical and electrochemical methods. The Strain 264 biofilm is stable in a wide potential range from −0.7 V to 1.0 V versus SCE; it is partially oxidized when the potential is above 1.0 V. In addition, the Strain 264 biofilm was used as an immobilization matrix for biosensor fabrication using horseradish peroxidase (HRP) as a model enzyme. Our electrochemical measurements show that the fabricated biosensor based on immobilized HRP in the Strain 264 biofilm exhibits a wide linear range (1–18 mM) and a high sensitivity (90 μA mM−1) for H2O2 detection, demonstrating that the formed biofilm provides a favourable microenvironment for enzyme to retain its activity. This study has also shown that direct growth of biofilms is a feasible and effective approach for promising applications of biofilms in electrochemical biosensor development.


Time Lapse Confocal Microscopy Studies of Bacterial Adhesion to Self-Assembled Monolayers and Confirmation of a Novel Approach to the Thermodynamic Model

June 2007

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36 Reads

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13 Citations

Langmuir

In this study, we use thermodynamic theory to develop a novel model that allows for the quantitative determination of the Gibbs free energy of adhesion for the initial bacterial attachment process. This model eliminates the need to calculate interfacial free energies and instead relies on easily measurable contact angles to determine DeltaG(adh). We experimentally verify our model using real-time observation of the initial attachment of Pseudomonas putida to methyl- and hydroxyl-terminated self-assembled monolayers. We also test the applicability of our model to a variety of experimental conditions using data available in the literature. We show that the initial attachment process is governed by dispersion forces and is accurately predicted by our model. Also, we find that our model is simple to apply and accurate for a variety of experimental conditions.


Citations (29)


... The constructed low-density biochip contains 12 probes in duplicate. Highly specific probes covering the taxa of interest were selected for subsequent testing from the publications (Al-Humam et al. 2018;Loy et al. 2002;Qin et al. 2003;Schraft and Griffiths 1995;van Waasbergen et al. 2000;Zinkevich and Beech 2000; https://pubmlst.org/ rhodococcus/info/Rhodococcus_ MLST_primers.pdf). ...

Reference:

Study of Arsenic-Contaminated Soil Bacterial Community Using Biochip Technology
Specific Oligonucleotide Primers for Detection of Lecithinase-Positive Bacillus spp. by PCR
  • Citing Article
  • June 1995

... P. spp. usually cause infections of gastrointestinal tract in human and animal [11][12][13]. Bacillus is Gram-positive, aerobic, ubiquitous bacteria that live in every natural environment [11][12][13][14]. Humans may come in contact with B. spp. that may cause illness in them [9]. ...

Bacillus cereus gastroenteritis
  • Citing Chapter
  • January 2006

... Nevertheless, occasional reports for more sever form of diarrhoeal type of illnesses, ubiquitous presence and heat-stable endospore forming nature of the organism. The unique properties such as heat resistance, endospore forming ability, toxin production and psychrotrophic nature give amplescope for this organism to be a prime cause of public health hazard [15]. This study revealed the incidence of B.cereus in stool of food poisoning patients was (4%). ...

Bacillus cereus food poisoning, in Cliver, D O and Riemann, H P
  • Citing Article
  • January 2002

... ZnO nanostructures have recently been created in various methods and grown on various surfaces with successfully, as hydrothermally [21,22]. ZnO nanostructures are widely employed in many different fields, electro-catalytic [23], light-emitting diodes [24], piezoelectric nanogenerators [25], ZnO nanoparticles quantum dot [26], solar cells [27], study light-emitting from ZnO nanowire [28], and electrochemical biosensoring [29]. ZnO's enormous potential for a wide range of useful applications, including optoelectronic devices (LEDs, lasers (nanogenerators), electronic devices (transistors), and sensors), catalysts, and active ingredients in sunscreens, is the main driving force behind ZnO research [30]. ...

Direct growth of biofilms on an electrode surface and its application in electrochemical biosensoring
  • Citing Article
  • December 2007

Journal of Electroanalytical Chemistry

... Taking all of these effects into consideration, we believe 1.5 mJ Á m À2 is a likely upper bound to the work of adhesion between the fresh spore adhesive and the PDMS tip. By way of comparison, we note that Pseudomonas putida bacteria under water [44] have been observed to adhere to a OH-terminated self-assembled monolayer (SAM) with a work of adhesion equal to 1.44 mJ Á m À2 , and to a methyl-terminated SAM with a work of adhesion of 7.66 mJ Á m À2 . ...

Bacterial Interaction with Hydrophobic and Hydrophilic Interfaces

... Prema Tompkinu [65], više od četiri CCP u jednom HACCP planu značajno otežava mogućnost realne primene takvog plana iz razloga prevelikog radnog angažmana i preobimne dokumentacije. Prevelik broj CCP nije preporučljiv ali nije ni približno "poguban" po bezbednost proizvoda kao njihov nedovoljan broj[55]. ...

HACCP: A Practical Approach, Sara Mortimore and Carol Wallace, Aspen Publishers, 403 pages, ISBN: 0-412-75440-1
  • Citing Article
  • August 1999

Food Research International

... It is recognized that proteins and carbohydrates possess hydrophobic and hydrophilic characteristics, respectively. Hence, proteins indicate more affinity for sludge than carbohydrates because of their hydrophobicity (Chen et al., 2017b;Gao et al., 2011Gao et al., , 2012. A lab-scale AnMBR was employed for over 160 d to estimate the potential to treat kraft pulp mill evaporator condensate. ...

Structure of cake layer in a submerged anaerobic membrane bioreactor
  • Citing Article
  • May 2011

Journal of Membrane Science

... Some models consider a unique partial differential equation that describes the growth of a single colony of bacteria [14], while others consider the interaction of a microbial population with a surrounding substrate of nutrients [16]. Other systems of partial differential equations consider the joint growth of different colonies of microbes in an environment of nutrients [15], and more complex models describe the interaction of the substrate with a biological bulk formed by a biologically active mass, an inert portion and the extracellular polymeric matrix [13]. Each of these (and other) models considers particular biological assumptions that in some degree represent realistic features observed in the laboratory but, as one would inevitably expect, the more assumptions used to derive a mathematical model, the more complicated the calculation of exact solutions for meaningful problems. ...

A Diffusion-Reaction Model of a Mixed-Culture Biofilm Arising in Food Safety Studies
  • Citing Chapter
  • January 2008

... Overall, the "global" scope employed and emphasis on elucidating local contamination risk factors are particularly pertinent given the myriad of local/regional conditions potentially influencing Cryptosporidium and/or VTEC prevalence and survival and ultimately their prevalence in groundwater. Similarly, the approach implemented follows reported regional variability in clinical cases and outbreaks linked to groundwater use (Watterworth et al., 2006;Avery et al., 2008;Bain et al., 2014;Saxena et al., 2015;Efstratiou et al., 2017a;Newell and La Ragione, 2018;Delahoy et al., 2018). The potential for (wide) regional variability in groundwater pathogenic prevalence and infection is perhaps best exemplified by the high rates of notifications of VTEC infections attributed to groundwater consumption in Ireland relative to EEA countries (Garvey et al., 2016;ECDC, 2019). ...

Survival of various ERIC-genotypes of Shiga toxin-producing Escherichia coli in well water
  • Citing Article
  • November 2006

Water Air and Soil Pollution

... Lm like many other bacterial species can form biofilms, which also counteract general cleaning and disinfection procedures and make it difficult to remove this pathogen from food processing surfaces (Bridier et al., 2015). It is of note that Lm can enter a VBNC state within a biofilm (Chae and Schraft, 2001;Giao and Keevil, 2014;Brauge et al., 2018). Highmore et al. (2018) showed that VBNC Lm adhering to the surface of spinach leaves are present at junctions and stomata, a location favoring biofilm formation on the leaf surface. ...

Cell viability of Listeria monocytogenes biofilms
  • Citing Article
  • February 2001

Food Microbiology