Exopolymer Production Research Articles

Isolation and characterization of halophilic bacteria producing exopolymers with emulsifying and antioxidant activities

Abstract Halophilic bacteria are considered a great source of new strains producing novel exopolymers with functional properties. In this work we isolated ten halophilic strains producing exopolymers from different hypersaline environments in Morocco. Phenotypic characterization showed that the strains were moderately halophilic, mesophilic and neutrophilic with the ability to produce some hydrolytic enzymes. Strains identification based on 16S rRNA gene sequences comparison showed that nine strains, designed as N1, N2, N5, N7, N8, N9, N10, N11 and N12 belong to Halomonas genus and one strain, designed as N4, to Marinobacter genus. The majority of the strains showed high levels of exopolymer production. The study of emulsifying and antioxidant activities revealed that all the polymers have an interesting emulsifying and antioxidant activities with the polymer from Marinobacter sp. N4 forming the highest and most stable emulsions and exhibiting the best antioxidant activity in comparison with other exopolymers produced by Halomonas strains. The obtained results demonstrate the great potential of exopolymers from halophilic bacteria to be applied as emulsifying and antioxidant agents in food, cosmetics and oil industries.

Rheo-chemical characterization of exopolysaccharides produced by plant growth promoting rhizobacteria

Abstract Background Modern agriculture recognizes soil biota as major contributors for availabilities of nitrogen and phosphorus to plants. Centralizing focus on exopolymer production of these living entities is need of time to emphasize their impact on soil structural restoration and heavy metal intoxication. Material and methods Mung bean rhizosphere collected from 25 locations was serially diluted and poured onto MY agar plates that were incubated for 120 h at 25°C to isolate bacteria having watery mucoidal appearance. Liquid broths of secluded cultures were then tested for optical scattering and were treated with ethanol to precipitate Exopolysaccharides (EPS) for their physicochemical characterization. Results Anion-exchange and high-performance size exclusion chromatographic analysis indicated two main monosaccharides, Mannose (52%) and Glucose (29%) fractions of EPS. EPS have substantial (0.2%) protein contents, capacity related to emulsify several hydrophobic substances. 0.5% EPS solution had low viscosity with pseudoplastic behaviour, least suspended particles producing less turbid solutions. Conclusion Six strains (M2, M3, M11, M16, M19, and M22) secreted noticeably greater amounts of exopolymers than other strains. Organic nature and pseudoplasticity of these exopolymers helps in soil structural restoration, sulfates and phosphates helps in heavy metals detoxication.

Microbial community changes during a toxic cyanobacterial bloom in an alkaline Hungarian lake.

The Carpathian Basin is a lowland plain located mainly in Hungary. Due to the nature of the bedrock, alluvial deposits, and a bowl shape, many lakes and ponds of the area are characterized by high alkalinity. In this study, we characterized temporal changes in eukaryal and bacterial community dynamics with high throughput sequencing and relate the changes to environmental conditions in Lake Velence located in Fejér county, Hungary. The sampled Lake Velence microbial populations (algal and bacterial) were analyzed to identify potential correlations with other community members and environmental parameters at six timepoints over 6weeks in the Spring of 2012. Correlations between community members suggest a positive relationship between certain algal and bacterial populations (e.g. Chlamydomondaceae with Actinobacteria and Acidobacteria), while other correlations allude to changes in these relationships over time. During the study, high nitrogen availability may have favored non-nitrogen fixing cyanobacteria, such as the toxin-producing Microcystis aeruginosa, and the eutrophic effect may have been exacerbated by high phosphorus availability as well as the high calcium and magnesium content of the Carpathian Basin bedrock, potentially fostering exopolymer production and cell aggregation. Cyanobacterial bloom formation could have a negative environmental impact on other community members and potentially affect overall water quality as well as recreational activities. To our knowledge, this is the first prediction for relationships between photoautotrophic eukaryotes and bacteria from an alkaline, Hungarian lake.

Biogeochemical cycling of gold: Transforming gold particles from arctic Finland

(Bio)geochemical cycling of gold (Au) has been demonstrated in present-day (semi)-arid, (sub)-tropical and temperate environment. Hereby biofilms on Au-bearing mineral- and Au-particle surfaces drive Au dispersion and reconcentration, thereby (trans)forming the particles. However, it is unknown if biogeochemical cycling of Au occurs in polar environments, where air temperatures can reach −40 °C and soils remain frozen for much of the year. Therefore, placer Au-particles, soils and waters were collected at two placer mining districts in arctic Finland, i.e., the Ivalojoki and Lemmenjoki goldfields. Sites were chosen based on contrasting settings ((glacio)-fluvial vs. glacial-till deposits) and depths (surface to 5 m below current surface). Gold particles were studied using a combination of tagged 16S rRNA gene next generation sequencing and electron microscopic/micro-analytical techniques. Across all sites a range of Au-particle morphologies were observed, including morphotypes indicative of Au dissolution and aggregation. Elevated Au concentrations indicative of Au mobility were detected in placer particle bearing soils at both districts. Typically Au-particles were coated by polymorphic biofilm layers composed of living and dead cells embedded in extracellular polymeric substances. Intermixed were biominerals, clays and iron-sulfides/oxides and abundant secondary Au morphotypes, i.e., nano-particles, micro-crystals, sheet-like Au, branched Au networks and overgrowths and secondary rims. Biofilms communities were composed of Acidobacteria (18.3%), Bacteroidetes (15.1%) and Proteobacteria (47.1%), with β-Proteobacteria (19.5%) being the most abundant proteobacterial group. Functionally, biofilms were composed of taxa contributing to biofilm establishment, exopolymer production and nutrient cycling, abundant taxa capable of Au mobilization, detoxification and biomineralization, among them Cupriavidus metallidurans, Acinetobacter spp. and Pseudomonas spp., were detected. In conclusion, these results demonstrate that placer Au-particle transformation and Au dispersion occur in cold, arctic environments. This corroborates the existence of biogeochemical Au cycling in present-day cold environments.

De novo evolved interference competition promotes the spread of biofilm defectors

Biofilms are social entities where bacteria live in tightly packed agglomerations, surrounded by self-secreted exopolymers. Since production of exopolymers is costly and potentially exploitable by non-producers, mechanisms that prevent invasion of non-producing mutants are hypothesized. Here we study long-term dynamics and evolution in Bacillus subtilis biofilm populations consisting of wild-type (WT) matrix producers and mutant non-producers. We show that non-producers initially fail to incorporate into biofilms formed by the WT cells, resulting in 100-fold lower final frequency compared to the WT. However, this is modulated in a long-term scenario, as non-producers evolve the ability to better incorporate into biofilms, thereby slightly decreasing the productivity of the whole population. Detailed molecular analysis reveals that the unexpected shift in the initially stable biofilm is coupled with newly evolved phage-mediated interference competition. Our work therefore demonstrates how collective behaviour can be disrupted as a result of rapid adaptation through mobile genetic elements.

Control of Grifola frondosa Morphology by Agitation and Aeration for Improving Mycelia and Exo-Polymer Production.

The present study describes the improved mycelia and exo-polymer production under control of Grifola frondosa morphology by changing the aeration rate and agitation intensity in a 25-L stirred fermentor. The aeration rate of 1.0vvm yielded a highest mycelia biomass of 24.754g/L with the lowest pellet percentage of 20.5%. The maximum exo-polymer (2.324g/L) was achieved at 0.75vvm with mycelia polysaccharide production (0.321g/g), whereas clumps and filaments dominated the ratios of 45.6 and 33.9%, respectively. The change of aeration rate and agitation intensity had slight influence on the monosaccharide compositions in exo-polymers and significantly affected glucose and mannose contents in the mycelia polysaccharides. These findings will provide a clue for exploring the relationship between fermentation parameters, morphologies, and polysaccharide synthesis pathway of G. frondosa.

A statistical approach on optimization of exopolymeric substance production by Halomonas sp. S19 and its emulsification activity

An exopolymer producing bacterial strain was identified as Halomonas sp. S19 by 16S rRNA gene sequencing isolated from Mandapam, Southeast coast of India. Strain S19 produces a significant amount of exopolymer (320 mg L−1) in a medium optimized with 2.5 % glucose, 0.6 % peptone, 7.5 % salt and pH 7.5 at 35 °C. The exopolymer consists of total sugars (65 %), proteins (4.07 %), uronic acids (8.08 %) and sulphur contents (6.39 %). FT-IR and 1H NMR analysis revealed the presence of functional groups corresponding to carbohydrates, proteins and sulphates. The exopolymer of Halomonas sp. S19 emulsifies different oils. However, 10 % exopolymer shows 55.18, 55.18, 49.81 and 24.62 % of emulsifying activity for sesame oil, coconut oil, paraffin and kerosene. The present study was focused on optimisation of exopolymer production using Box–Behnken experimental design and its possibility for potential emulsification index.

Production of exopolymers (EPS) by cyanobacteria: impact on the carbon-to-nutrient ratio of the particulate organic matter

Freshwater cyanobacteria can produce large amount of mucilage, particularly during large 11 blooms. The production of these carbon-rich exopolymers (EPS) should influence the carbon-to-12 nutrient ratios of the organic matter (OM), which are regularly used as a proxy for the herbivorous 13 food quality. However, little is known about the consequences of EPS production on the carbon-to-14 nutrient ratio of the OM. Two EPS forms can be distinguished: the free fraction composed of Soluble 15 Extracellular Polymeric Substances (S-EPS) and the particulate fraction corresponding to the 16 Transparent Exopolymer Particles (TEP). The aim of the study was to determine whether the TEP and 17 S-EPS productions by cyanobacteria influence the carbon-to-nutrient ratios of the particulate OM 18 (POM). Five cyanobacteria species were grown in batch culture and characterized in terms of 19 photosynthetic activity, EPS production, and C, N, P contents. The variability in EPS production was 20 compared with the variability in stoichiometry of the POM. Most of cyanobacteria live in association 21 with heterotrophic bacteria (HB) within the mucilage. The effect of the presence/absence of HB on 22 EPS production and the carbon-to-nutrient ratios of the POM was also characterized for the 23 cyanobacteria Microcystis aeruginosa. We showed that TEP production increased the carbon-to-24 nutrient ratios of the POM in the absence of HB, while the stoichiometry did not significantly change 25 when HB were present. The C:N ratio of the POM decreased with production of S-EPS by the five 26 species. Lastly, the three colonial species (Chroococcales) tend to produce more TEP than the two 27 filamentous species (Oscillatoriales), with the two picocyanobacteria being the most productive of 28 both TEP and S-EPS. 29 30 2

Continuous harvesting of microalgae by new microfluidic technology for particle separation

A new microfluidic chip based on a trilobite structure, designed for continuously concentrating particles in moving fluids, was investigated as a pre-concentration method for microalgal harvesting. The chip has a 5-μm gap limit and was tested for concentrating the microalgae Rhodomonas baltica, Chaetoceros sp. and Thalassiosira weissflogii. The chip was able to concentrate rigid cells and to sort them according to size. However, optimization with respect to cell properties, such as size and flexibility, needs further work. Although no clogging of the chip was seen for R. baltica and Chaetoceros sp., production of exopolymers by T. weissflogii made harvesting challenging for this species. The Trilobite™ microfluidic chip appears to be a promising tool for pre-concentrating microalgae that are difficult to harvest due to their repelling properties or small size.

Corrosion of carbon steel by sulphate reducing bacteria: Initial attachment and the role of ferrous ions

A study of the effect of ferrous ions on the initial attachment of sulphate reducing bacteria (SRB) and subsequent corrosion of carbon steel has been performed. It was found that the initial bacterial attachment process is complex, depending upon time period investigated. Early stages (⩽60min) of attachment showed no dependence on the iron level in the media. After 60min, more attachment and exopolymer production was observed in iron rich medium compared to iron deficient medium. The results suggest that monitoring of ferrous ion levels might be helpful in detection of MIC attack by SRB.

Screening metal-dye-tolerant photoautotrophic microbes from textile wastewaters for biohydrogen production

In the present study, tolerance of ten microalgal strains isolated from wastewaters of different textile mills in relation to two metals and dyes was studied based on cell growth estimated spectrophotometrically. Three cyanobacterial strains that were found to tolerate both Cr(VI) and Co(II) along with the dyes reactive red 198 (RR 198) and crystal violet (CV) were investigated further for the concen- tration of various photosynthetic pigments and exopolymer production in the presence of the dyes and metals. All three tolerant species—Nostoc linckia HA-46, Myxosarcina spectabilis HP-43 and Gloeocapsa calcarea HP-45—showed a significantly higher concentration (P 0.05). Production of hydrogen by these photoautotrophic microbes was moderate (19-28 nmol h �1 mg �1 dry wt). The best performing strain, N. linckia, when examined further for its hydrogen production potential in the presence of the two dyes and metals, showed significantly higher rates of hydrogen production in the presence of Cr, Co and RR 198. Its hydrog- enase activity also followed the same trend. Immobilization of the microbe into alginate beads almost doubled the hydrogen production by the organism in the control as well as in the presence of suitable concentrations of the two metals (10 mg L �1 ) and dyes (50 mg L �1 ).

Surface adhesion of microphytobenthic biofilms is enhanced under Hediste diversicolor (O.F. Müller) trophic pressure

In soft-bottom tidal flats, sediment stability is one of the crucial parameters modulating the abundance and composition of benthic assemblages. It is dependent on a wide range of variables, both abiotic and biotic. Investigating how these variables and their interactions influence sediment stability is therefore essential to understand how benthic assemblages are distributed in their environment. In this context, we designed a microcosm study to examine how microorganisms and macrofauna interact to alter sediment stability. We cultured a natural microbial community, enriched with diatoms, both alone and together with the common ragworm Hediste diversicolor, and monitored their effects on photosynthetic biomasses, bacterial abundances, exopolymer secretions and sediment stability. We also assessed the consumption of biofilm by worms using fatty acid biomarkers. Our results demonstrate that even if H. diversicolor fed on diatoms, they stimulated biofilm development, in terms of photosynthetic biomass and exopolymer production. Also, sediment cohesiveness was enhanced when both diatoms and H. diversicolor were cultured together; this result was unexpected since macrofauna, through consumption of microorganisms and modification of sediment properties, is often considered to have a destabilising effect on sediment. Predicting the effect of macrofauna on microphytobenthic biofilms and their associated influence of sediment stability is therefore not straightforward. Similar experiments including different types of organisms or more complex assemblages might help to further characterise the effect of biota on sediment stability.

Effects of Marinobacter adhaerens HP15 on polymer exudation by Thalassiosira weissflogii at different N:P ratios

In the ocean, exopolymer accumulation and the resulting aggregation of marine phytoplankton drive the flux of sinking organic matter. Little is known about the contribution of bacteria to the release and build-up of such exudates. We describe an in-depth investigation of exopolymer production under differing nutrient conditions using a diatombacteria model system. Responses of the marine diatom Thalassiosira weissflogii to different nutrient re gimes and the impact of the co-incubated bacterium Marinobacter adhaerens on algal exudation were evaluated by ana- lyzing quantity and quality of exudation products. Cul- tures of T. weissflogii were grown at nutrient-balanced conditions (Redfield ratio N:P = 16) as well as at nitro- gen- or phosphorus-depleted conditions (N:P = 1 and N:P = 95, respectively) in the presence or absence of M. adhaerens. The impact of M. adhaerens on the con- centration of dissolved organic carbon and transparent exopolymer particles (TEP), as well as on the composi- tion of amino acids and carbohydrates, depended on the nutrient regime. Under nutrient-balanced con - ditions, M. adhaerens stimulated both T. weissflogii growth and TEP production. Under nutrient-depleted conditions, TEP production was enhanced regardless of whether bacteria were present. Phosphorus limita- tion resulted in an appreciable change in the %mol composition of dissolved amino acids in xenic and axenic treatments. Differential lec tin staining revealed that the presence of M. adhae rens enhanced and modified the pro duction of specific extracellular sub- stances. A better understan ding of the effects of diatombacteria interactions on the accumulation of exudation products is crucial in modelling and predict- ing consequences of environmental changes on oceanic organic matter and nutrient cycling.

Metal tolerance of an indigenous cyanobacterial strain, Lyngbya putealis

Response of an indigenous cyanobacterial strain ( Lyngbya putealis) isolated from contaminated site to increasing levels of copper and cobalt was investigated in single metal systems. This cyanobacterial strain showed better response when the medium was spiked with metal. As compared to cobalt treatment, copper had more favorable effect. In single metal systems (copper or cobalt), metal treatments positively effected the cyanobacterial growth as indicated by higher concentration of the primary and accessory photosynthetic pigment (chlorophyll and phycobiliproteins), and biomass production at 0.5 mg/L ( M 0.5) as compared to that at control ( M 0). Exopolymer production (exopolysaccharides and extracellular proteins) too tended to increase significantly in response to both copper and cobalt in L. putealis and found to be maximum at metal concentration M 2.0. This species also showed increased accumulation of starch and carbohydrates in presence of metal (copper or cobalt) at M 0.1. But the overall response was better for copper as compared to cobalt in single metal systems for almost all the studied parameters which show that the strain offered good protection against copper but was sensitive to cobalt.

Discriminating multi-species populations in biofilms with peptide nucleic acid fluorescence in situ hybridization (PNA FISH).

BackgroundOur current understanding of biofilms indicates that these structures are typically composed of many different microbial species. However, the lack of reliable techniques for the discrimination of each population has meant that studies focusing on multi-species biofilms are scarce and typically generate qualitative rather than quantitative data.Methodology/Principal FindingsWe employ peptide nucleic acid fluorescence in situ hybridization (PNA FISH) methods to quantify and visualize mixed biofilm populations. As a case study, we present the characterization of Salmonella enterica/Listeria monocytogenes/Escherichia coli single, dual and tri-species biofilms in seven different support materials. Ex-situ, we were able to monitor quantitatively the populations of ∼56 mixed species biofilms up to 48 h, regardless of the support material. In situ, a correct quantification remained more elusive, but a qualitative understanding of biofilm structure and composition is clearly possible by confocal laser scanning microscopy (CLSM) at least up to 192 h. Combining the data obtained from PNA FISH/CLSM with data from other established techniques and from calculated microbial parameters, we were able to develop a model for this tri-species biofilm. The higher growth rate and exopolymer production ability of E. coli probably led this microorganism to outcompete the other two [average cell numbers (cells/cm2) for 48 h biofilm: E. coli 2,1×108 (±2,4×107); L. monocytogenes 6,8×107 (±9,4×106); and S. enterica 1,4×106 (±4,1×105)]. This overgrowth was confirmed by CSLM, with two well-defined layers being easily identified: the top one with E. coli, and the bottom one with mixed regions of L. monocytogenes and S. enterica.SignificanceWhile PNA FISH has been described previously for the qualitative study of biofilm populations, the present investigation demonstrates that it can also be used for the accurate quantification and spatial distribution of species in polymicrobial communities. Thus, it facilitates the understanding of interspecies interactions and how these are affected by changes in the surrounding environment.

Exopolysaccharide Production from Sweet Potato-Shochu Distillery Wastewater by Lactobacillus Sakei CY1

ABSTRACTIn order to examine a potential use of sweet potato-shochu distillery wastewater, we investigated the production of exopolysaccharides (EPSs) by bacteria grown in wastewater-supplemented media. The supernatant of the clarified distillery by-product contains 40.5 g/L protein, 3.47 g/L nitrogen, and 32 g/L total organic carbon. Lactobacillus sakei CY1, which was obtained from cucumber fermentation, was cultured in this wastewater for exopolymer production. The highest yield of Lactobacillus sakei EPS were obtained at 4.6 g/L on basal medium supplemented with 75% shochu wastewater at 30°C and pH 6.2. Under these culture conditions, the EPSs produced comprised 25.5% glucose and 13.2% galactose, along with other sugars. The sweet potato-shochu distillery wastewater contains nutrients that support Lactobacillus sakei CY1 growth. Because the culture media required no or very little supplementation with expensive commercial nutrients, this process was not expensive.

Bacterivorous nematodes stimulate microbial growth and exopolymer production in marine sediment microcosms

The cohesive strength of intertidal soft sediments depends on a large range of physico- chemical parameters, but the production of exopolymers by the inhabiting organisms is increasingly recognized as a major stabilizing factor. It is likely that the vast majority of these polymers are pro- duced by microorganisms but very few studies have addressed the impact of benthic meiofauna on this microbial production. The major aim of this study was thus to estimate the impact of nematodes (often the main contributor to meiofauna abundance and biomass in temperate intertidal habitats) on the EPS (extracellular polymeric substances) production of marine sediments. Bacterivorous nema- todes Diplolaimelloides meyli Timm, 1961 and D. oschei Meyl, 1954, bacteria and diatoms were grown in laboratory experiments both separately and together to estimate their respective influence. Our experiment revealed a positive impact of bacterivorous nematodes on microbial density and EPS production. Surprisingly, the biofilm structure (in terms of microbial abundance/biomass and EPS content) was better explained by the complexity (i.e. the number of trophic levels) of the assemblages rather than by any specific types of organisms involved in the experiment.

Sedimentary organic matter distributions, burrowing activity, and biogeochemical cycling: Natural patterns and experimental artifacts

The coupling between biogenic reworking activity and reactive organic matter patterns within deposits is poorly understood and often ignored. In this study, we examined how common experimental treatments of sediment affect the burrowing behavior of the polychaete Nephtys incisa and how these effects may interact with reactive organic matter distributions to alter diagenetic transport – reaction balances. Sediment and animals were recovered from a subtidal site in central Long Island Sound, USA. The upper 15 cm of the sediment was sectioned into sub-intervals, and each interval separately sieved and homogenized. Three initial distributions of sediment and organic substrate reactivity were setup in a series of microcosms: (1) a reconstituted natural pattern with surface-derived sediment overlying sediment obtained from progressively deeper material to a depth of 15 cm (Natural); (2) a 15 cm thick sediment layer composed only of surface-derived sediment (Rich); and (3) a 15 cm thick layer composed of uniformally mixed sediment from the original 15 cm sediment profile (Averaged). The two last treatments are comparable to that used in microcosms in many previous studies of bioturbation and interspecific functional interaction experiments. Sediment grain size distributions were 97.5% silt-clay and showed no depth dependent patterns. Sediment porosity gradients were slightly altered by the treatments. Nepthys were reintroduced and aquariums were X-rayed regularly over 5 months to visualize and quantify spatial and temporal dynamics of burrows. The burrowing behaviour of adult populations having similar total biovolume, biomass, abundance, and individual sizes differed substantially as a function of treatment. Burrows in sediment with natural property gradients were much shallower and less dense than those in microcosms with altered gradients. The burrow volume/biovolume ratio was also lower in the substrate with natural organic reactivity gradients. Variation in food resources or in sediment mechanical properties associated with treatments, the latter in part coupled to remineralization processes such as exopolymer production, may explain the burrowing responses. In addition to demonstrating how species may respond to physical sedimentation events (substrate homogenization) and patterns of reactive organic matter redistribution, these experiments suggest that infaunal species interactions in microcosms, including the absolute and relative fluxes of remineralized solutes, may be subject to artifacts depending on exactly how sediments are introduced experimentally. Nonlocal transport and cylinder microenvironment transport – reaction models readily demonstrate how the multiple interactions between burrowing patterns and remineralization rate distributions can alter relative flux balances, decomposition pathways, and time to steady state.

Production of mycelial biomass and exo-polymer by Hericium erinaceus CZ-2: Optimization of nutrients levels using response surface methodology

The Doehlert experimental design was used to optimize the production of mycelial biomass and exopolymer from Hericium erinaceus CZ-2 in this study. Statistical analysis showed that the linear and quadric terms of 3 variables: corn flour, yeast extract, and corn steep liquor had significant effects. The optimized combination of these 3 variables was confirmed through validation experiments. The optimal conditions for higher production of mycelial biomass (19.92 g/L) were estimated when the media composition concentrations were set as: 30.85 g/L, corn flour; 2.81 g/L, yeast extract; 16.9 mL/L, corn steep liquor; 10 g/L, glucose; 1 g/L, KH2PO4; and 0.5 g/L, MgSO4·7H2O; while a maximal exo-polymer yield (1.653 g/L) could be achieved when setting concentrations of: 32.71 g/L, corn flour; 2.35 g/L, Yeast extract; 14.42 mL/L, Corn steep liquor; 10 g/L, glucose; 1 g/L, KH2PO4; and 0.5 g/L, MgSO4·7H2O. The upscale production was also investigated using a 15 L fermentor using the optimized medium.

Incorporating pore blocking, cake filtration, and EPS production in a model for constant pressure bacterial fouling during dead-end microfiltration

Microfiltration is used in a wide range of municipal and industrial settings to remove particulate matter including pathogenic microorganisms such as bacteria and protozoa. As more water is filtered at constant pressure, the accumulation of retained particles on the membrane decreases the filtration rate; a process commonly referred to as fouling. Mathematical treatment of flux decline has proved to be a useful tool in diagnosing filtration data even though the mathematical underpinnings are not completely understood. In particular, little is known about the transition between fouling phenomena (e.g. pore blocking to cake filtration). Moreover, less is known about the effect of extracellular polymeric substances (EPS) production by bacteria when they accumulate on a membrane over extended durations. In this manuscript, we develop a novel approach to model bacterial microfiltration by considering the effects of both differential binding and exopolymer production. Spatial gradients in bacteria concentrations initially occur due to the non-uniform membrane surface porosity and differential deposition caused by the stochastic nature of microorganism adhesion. These heterogeneities in bacterial deposition and associated pore blocking result in variable secretion of extracellular polymers. Long-term fouling is quantified as the cumulative resistance posed by both bound bacteria and EPS. We compare numerical simulations quantitatively and qualitatively to previously published experimental data and investigate variations of microbial deposition patterns across the membrane. We find substantial agreement between the model and experimental observations. We are also able to conclude that fluid dynamics must be important if the dominant variability is in the membrane structure, rather than in bacterial adhesion. However, variation in bacterial adhesion alone can also induce substantial spatial heterogeneity.