A computational model for microbial colonisation of an antifouling surface

Biofouling of marine surfaces such as ship hulls is a major industrial problem. Antifouling (AF) paints delay the onset of biofouling by releasing biocidal chemicals. We present a computational model for microbial colonization of a biocide-releasing AF surface. Our model accounts for random arrival from the ocean of microorganisms with different biocide resistance levels, biocide-dependent proliferation or killing, and a transition to a biofilm state. Our computer simulations support a picture in which biocide-resistant microorganisms initially form a loosely attached layer that eventually transitions to a growing biofilm. Once the growing biofilm is established, immigrating microorganisms are shielded from the biocide, allowing more biocide-susceptible strains to proliferate. In our model, colonization of the AF surface is highly stochastic. The waiting time before the biofilm establishes is exponentially distributed, suggesting a Poisson process. The waiting time depends exponentially on both the concentration of biocide at the surface and the rate of arrival of resistant microorganisms from the ocean. Taken together our results suggest that biofouling of AF surfaces may be intrinsically stochastic and hence unpredictable, but immigration of more biocide-resistant species, as well as the biological transition to biofilm physiology, may be important factors controlling the time to biofilm establishment

Dataset for the Southampton doctoral thesis: Developing Remote Sensing Tools for Quantifying Ship-Borne Marine Fouling Biofilms

Supporting data for thesis including spectra, pigment data, and images</span

A marine biofilm flow cell for in situ determination of drag, structure and viscoelastic properties

It is not straightforward to link biofilm parameters to frictional drag, likely because of the heterogeneous nature of slime. Here we present the design and calibration of a pragmatic, small scale flow-cell in which biofilms can either be cultured under flow or grown statically and then assessed under flow for drag and other properties. The flow cell test section comprised a rectangular channel (870x10x55mm) constructed by sandwiching together rigid opaque PVC panels and side panels of clear acrylic, which allow natural light to enter. A maze-like entry section evened out the inlet flow. Seawater flow rate through the channel was monitored by an in-line digital flowmeter, and pressure drop (ΔP) along the test section was measured using a differential pressure sensor. The friction coefficient (Cf) of the flow cell was found by measuring the ΔP at various flow velocities (u) over the entire pump range (maximum Re ~22,000). Flow cell calibration was carried out using a clean inert marine coating, and various roughness grades (P40, P80 and P120) of waterproof sandpaper sheets, fixed to the wide faces of the channel, to find Cf for each rigid roughness. ΔP was proportional to u2, indicating flow was turbulent in this region (R = 99%). When fouled panels are used as the channel floor and a clear acrylic panel as the ceiling, the flow cell allows for simultaneous measurement of Cf of the lower surface and biofilm physico-mechanical properties (e.g. thickness, roughness, viscoelasticity) by optical coherence tomography (OCT) imaging, which generates depth profiles of translucent samples. Changes to biofilm physico-mechanical properties during flow loading/unloading cycles, determined by image analysis, can be compared to simultaneously collected ΔP measurements scaled to a one-sided sandpaper Cf calibration. Future experiments will assess physico-mechanical and drag properties of marine fouling biofilms in flow using ΔP and OCT

A marine biofilm flow-cell for screening antifouling marine coatings using optical coherence tomography

A novel fouling marine flow-cell was designed and fitted with a top clear 5 mm thick plastic lid to allow real time imaging of the biofilm using optical coherence tomography (OCT). The OCT was used to analyse biofilm removal and mechanical properties during shear-stress experiments. The OCT measures intensity depth profiles from translucent samples such as biofilms. Consecutive scans provide a cross-sectional view of the biofilm structure which are then combined to give volumetric representations. The scanning speed of the OCT reached up to 30,000 scans/s and covers a field of view of 9x9 mm2. The bottom plate of the flow-cell was machined to allow the insertion of fouled microscope slides (25 x 55 x 1 mm). Marine biofilms were grown on spray coated (inert coating) slides in seawater for up to 2 years to test mechanical properties (triplicates). Marine biofilms were grown dynamically on 6 different antifouling coatings (A, B, C, D, E, F) for 8 weeks to test biofilm removal (duplicates). Marine biofilms were also grown statically and dynamically on an antifouling coating G to assess biofilm removal. Biofilm mechanical behaviour and removal were assessed by increasing (load cycle) or decreasing (unload cycle) the flow velocity (and therefore shear stress) in a stepwise manner over the entire pump range. Each step interval lasted 30 s except at the highest flow which was held for 5 min before starting the unloading cycle. The OCT was set to measure 10 xz-cross sections along the flow for each velocity step. 3D C-scans were also acquired before the loading cycle and at the end of the unloading cycle. The OCT images were analysed using ImageJ and Matlab. The angle of deformation of individual biofilm clusters were measured for each shear stress to obtain a stress/strain curve. Stress/strain curves showed classic viscoelastic biofilm behaviour. From the initial linear region of the load cycle the shear modulus (G) was estimated to be G = 46.2 ±5.43 Pa (n = 3). The biofilm also showed a residual strain εR = 0.28± 0.01 (n = 2). The % cross-sectional area removed (%A) as a function of the shear stress was measured from the OCT images for each antifouled slide. The %A value increases exponentially for all the antifouling coatings until a shear stress of ~25 Pa, when it reached a plateau. Considering a shear stress of 15 Pa, %A of coating C (A% = 75%) was significantly higher than the value of the other coatings showing best performance. The %A of the biofilm grown on coating G statically (A% = 68%) was lower than the value of the biofilm grown dynamically (A% = 82%). These results show that the marine biofilm flow-cell combined with OCT can be used to assess mechanical properties of marine biofilms and detect differences (in terms of removal) in biofilms grown on different coatings. Future testing will focus on assessing how mechanical properties of biofilms interact with their physical properties (roughness, thickness, extent) to produce drag

A marine biofilm flow cell for in situ screening marine fouling control coatings using optical coherence tomography

A novel fouling marine flow cell was designed and fitted with a clear plastic lid to allow real-time imaging of biofilms using optical coherence tomography (OCT). Marine biofilms were grown under controlled shear flow on coupons coated with 6 different biocidal antifouling coatings (SPC1, SPC2, SPC3, SPC4, CDP1 and CDP2, AkzoNobel) and one inert coating which contained no biocidal actives (NB-D) for 8 weeks. One set of coupons coated with NB was statically immersed in sea water during the same time period (NB-S). Biofilm removal was assessed by increasing the flow velocity while OCT simultaneously measured the biofilm cross-sectional area (CSA). The highest initial removal rates were observed for NB-S, NB-D, and SPC2. Percent biofilm cross-sectional area reduction (%CSAred) was higher on SPCs (&gt;60%) compared to CDPs (&lt;50%). SPCs had the highest percent reduction in biofilm surface area coverage (%SACred &gt;60%) compared to the CDPs (&lt;20 %). The marine biofilm flow cell combined with OCT can be used to screen for coating-specific differences in biofilm growth and removal in real time rather than traditional before and after surface area coverage measurements. Future testing will focus on how the biofilm-coatings interactions interact with biofilm mechanical and structural properties to produce drag

A marine biofilm flow cell for in situ determination of drag and biofilm structure

It is not straightforward to link biofilm parameters to frictional drag, because of the heterogeneous distribution and viscoelasticity of the produced matrix. Here we present the design and calibration of a flow cell in which marine biofilms can be cultured under flow and then assessed for drag, structural and mechanical properties. The flow cell test section comprised a rectangular channel constructed by sandwiching together rigid PVC panels and side panels of clear acrylic, which allow natural light to enter. The Fanning friction factor (Cf) of the flow cell was found by measuring the pressure drop (ΔP) at various flow velocities (u). Flow cell calibration was carried out using a clean inert marine coating, and various roughness grades of sandpaper sheets to find Cf for each rigid roughness. ΔP was proportional to u2, indicating flow was turbulent (R2 = 0.99). The top panel of the flow cell can be substituted with a clear acrylic lid to allow simultaneous measurement of Cf and biofilm physico-mechanical properties by optical coherence tomography (OCT). Here, we demonstrated that the flow cell can be used to image microbial fouling using OCT. Future experiments will assess physico-mechanical and drag properties of marine fouling biofilms under flow

Dataset to support the journal article: &quot;Surface properties influence marine biofilm rheology, with implications for ship drag&quot;

The data is to support the journal article: Surface properties influence marine biofilm rheology, with implications for ship drag, published in the Soft Matter Journal. Data included are all excel spreadsheets; some present the raw data with mean +/- SD calculated and others show data that have been inputted into equations to give required results. Some figures used in the manuscripts are also included in the spreadsheets.</span

A rapid benchtop method to assess biofilm on marine fouling control coatings

A rapid benchtop method to measure the torque associated with minidiscs rotating in water using a sensitive analytical rheometer has been used to monitor the drag caused by marine fouling on coated discs. The method was calibrated using sandpaper surfaces of known roughness. Minidiscs coated with commercial fouling control coatings, plus an inactive control, were exposed in an estuarine harbour. After 176 days the drag on the fouling control-coated discs, expressed as a moment coefficient, was between 73% and 90% less than the drag on the control coating. The method has potential use as a screen for novel anti-fouling and drag reducing coatings and surfaces. Roughness functions derived using Granville’s indirect similarity law are similar to patterns found in the general hydrodynamics literature, and so rotational minidisc results can be considered with reference to other fouling drag datasets