An eco-friendly way to prevent biofouling
Guezennec, J., Herry, J.M., Kouzayha, A., Bachere, E., Mittelman, M.W., Noelle, M., Fontaine, B., (2012), Exopolysaccharides from unusual marine environments inhibit early stages of biofouling, International Biodeterioration & Biodegradation, 66(1):1-7
Marine biofouling causes numerous problems for water-contacting structures. These detrimental effects are due to microbial biofilm formation and successional colonisation of macroorganisms. Prevention techniques rely on antimicrobial agents, which despite being successful, also show toxicity to non-target organisms and other non-toxic surface modification techniques have shown limited efficiency with some causing partial detachment of the biofilm, leading to a high risk of microbial-induced corrosion. It is therefore necessary to develop an effective and environmentally compatible technology to prevent such problems.
One approach is through the coating of surfaces with specific exopolysaccharides (polymers secreted by microorganisms), who’s physical and chemical nature could be important in the prevention of the attachment process, therefore inhibiting biofilm formation and thus biofouling. This study evaluates the antifouling potential of several exopolysaccharides (EPS) produced under laboratory conditions by several bacteria. They were tested for their ability to form a stable film in order to prevent biofilm formation on a glass plate which was immersed in natural flowing seawater containing samples of EPS.
The 5 EPS producers used were; Alteromonas, Pseudoalteromonas, Vibrio and Pyrococcus sp. Once the EPS samples were recovered through centrifugation and ultrafiltration, its composition, including sugars, uronic acids and non-carbohydrate substituents were determined using colometric methods and HPLC analysis. Antimicrobial activity against several bacteria and cellular toxicity was also analysed.
The samples contained uronic acids, sugars including mannose and glucose, along with acetate, lactate and pyruvate, which are of high relevance to the structure-function relationships. Despite several studies suggesting that EPS have antimicrobial effects against various bacteria, this study found no evidence of any antimicrobial activity or cytotoxicity,. This could be due to the different methodologies used, including culture conditions or the use of purified EPS rather than crude exopolymeric substances used in previous studies.
In the absence of any treatments, after 5 days of immersion, the glass surfaces were covered around 70% by a biomass mainly comprised of bacteria and few diatoms. However, after pre-conditioning the glass with the different EPS, bacterial colonisation did not exceed 20%, with less than 11% of the surface colonised with most of the samples. SEM showed that biopolymers remained on the surface after 72hours, suggesting the presence of a homogenous film.
The stability of the film is thought to be due to the chemical composition of EPS, with the possible high uronic acid content encouraging formation of the film on the glass. Similarly, sugars, charged polysaccharides and proteins are known to mediate mechanical stability of biofilms (Flemming and Wingender 2010). The author’s note that based on their preliminary data, it is difficult to correlate a particular EPS composition with the inhibition of bacterial attachment and biofilm formation, therefore further work should be done to deduce the key components, including molecular weight and spatial orientation leading to possible steric hindrance. Additionally, the presence of a polymeric film on the surface can induce changes in the hydrophobic/hydrophilic balance and interactions between bacterial cells and surfaces, suggesting microbial adhesion strongly depends of the hydrophobic–hydrophilic structure of interacting surfaces and should be further analysed.
Overall, there are clear advantages to using natural polymers, especially bacterial EPS for antifouling purposes through permanent coating. They prevent bacterial adhesion and subsequent biofilm formation and moreover, do not contain any toxic molecules which could affect the local ecosystem and are easily produced with simple cultivation. The specific mechanisms and compositions should be further explored.
Additional reference: Flemming, H.C., Wingender, J., (2010), The biofilm matrix, Nature Reviews Microbiology, 8:623-633
6 comments:
Just to add...The bacteria used in this experiment and many previous similar experiments are mainly mesophilic heterotrophic bacteria. Interestingly, thermophilic and hyperthermophilic organisms are considered more biotechnologically attractive due to their production of thermostable enzymes. Also there has been characterisation of several polymers from these bacteria, with considerable knowledge of their composition. It would be beneficial to focus efforts on screening the potential of these polymers and it may help to further establish how the specific compositions affect bacterial adhesion and which are more favourable. Moreover, the EPS film produced in this experiment was present for 72hours, however after this time it appeared to have been disrupted. Perhaps the polymers from thermophilic bacteria could maintain their presence for longer due to their more stable compounds, thus providing more efficient means to prevent biofilm formation.
Hi Jelena
Anti biofouling research seems to be a major area. I did a review a week or so ago about trying to prevent biofilm formation by disrupting quorum sensing. It is good to see that environmentally friendly methods are being developed.
Regarding your review, I was just wondering if there was any differences in the effectiveness of the different EPS from the five species? I am guessing the EPS structures might differ slightly between species, maybe.
Hi Lee,
Well in terms of the difference in composition, the EPS samples were all branched polymers aside from one strain from Vibrio spp. which was linear. The compositions also varied slightly in the percentage of uronic acid and sugar present.
Generally, there was little difference in efficiency between the different EPS. They did find that EPS recovered from Vibrio and 3 Alteromonas sp. exhibited best efficiency, resulting in only around 11% coverage of the glass with biofilms, whereas the rest generally resulted in around 20% coverage. Another difference noted between them was that the majority of EPS films that were present on the glass remained there throughout the experiment, however EPS from a Pseudomonas sp. was disrupted after 72hours into the experiment. Similary, one EPS sample from an Alteromonas sp. showed disruption in its film after 72hours, which I noticed happened to have the higher % of sugars and the lowest % of Uronic acids compared to all the EPS samples.
All in all though, this slight difference in efficiency was not found to be significant.
You said thermophilic bacteria are more biotechnologically attractive because of their thermostable enzymes, what temperatures are these bacteria used at though, is thermostability really necessary?, or is it better to have a wider variety of bacteria that produce better EPS?
I have also looked at a paper and have reviewed it now about another environmentally friendly way to prevent biofouling also. Take a look if you are interested, environmentally friendly is definitely the way to go after TBT was banned in '82.
Well the authors of this paper say they should be used because of their thermostable enzymes. I wasn't sure how thermostability itself would be beneficial, but I did find several papers that discuss that many thermophilic bacteria have been found to produce a number of 'unusual' EPS with interesting chemical and physical properties. I assume this is why they would be appealing to use as their composition could be make them more successful for anti-fouling strategies. Moreover, compared to the EPS produced by some of the bacteria used in this experiment, some EPS from these thermophilic bacteria have been better characterised and more is known of their composition. In addition, the paper states that extremophilic bacteria produce thermostable DNA-modifying enzymes which are more appealing for the application. I assume that their stability could mean that the EPS produced would be more stable and would not be disrupted as easily (like some of the EPS in this experiment which were disrupted after 72hours). Moreover, another paper describes how some enzymes are involved in EPS production and can improve its stability, specifically Beta-galactosidase, which is thermostable and thermoresistant. So essentially, more stable enzymes produce more stable EPS, possibly more resistant to degradation. Hope that explains it a bit better! And yes I’ll definitely have a read. It’s good that more and more eco-friendly ways are being found to tackle the problem, instead of just sticking to easy solutions like biocides and causing all sorts of environmental problems!
The wealth of research on this subject seems almost overwhelming. It appears to be a complex issue with a deeply practical industrial and ecological incentive to be understood.
I have been looking into the anti-biofilm molecules secreted by a few strains of alteromonas which have been associated with obstructing the formation of biofilms by other marine bacteria. From this reading i have noted that various differences in the physical behaviour and spectra of action have been observed between molecules of diferent strains within the alteromonas sp. - this to me showed 'another level' to the potential multifaceted parameters characterising the formation of a biofilm. Further investigation on a 'species' level seems needed to fully develop further methods of control derived from these molecules.
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