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Role of microbial mats in bioremediation of hydrocarbon polluted coastal zones

Obiettivo

PROBLEMS TO BE SOLVED
This project represents a comprehensive study of the interactions between i) physical, and biogeochemical variables and ii) the microbial processes and biodiversity found in microbial mat systems that develop at the sediment surface in coastal zones, and how these interactions can be exploited to bioremediation oil polluted sediments. The information gained from these studies will substantially advance our knowledge and understanding of microbial mat ecosystems and will help to predict their response(s) to oil pollution. This information will be primarily obtained by the evaluation of the potential of microbial mats for bioremediation of oil polluted coastal zones.
SCIENTIFIC OBJECTIVES AND APPROACH
The scientific objectives are to understand the role of microbial mats in the bioremediation of oil-polluted shallow coastal marine environments. For that, specific actions will be undertaken to determine the biogeochemical responses and the change in microbial diversity of selected microbial mats in different environments when subjected to oil pollution or in some microbial mats maintained in mesocosms under controlled conditions and exposed to various hydrocarbons and/or crude oils. A second step of the project will be to investigate the behaviour and rate of degradation of hydrocarbon molecules when introduced into experimental microbial mats and to assess the extend of oil degradation (linear, branched and polycyclic hydrocarbons). Finally, an important part of the project will be to isolate, characterize and determine the physiology and biochemistry of the dominant micro organisms involved in hydrocarbon degradation in microbial mats.
The research programme will be organised into four work packages:
Ecosystems level (Work package 1): Different microbial mats will be investigated for biogeochemistry with standard and micro sensor techniques, for microbial diversity with microscopy and molecular biology techniques. Chemical analyses of hydrocarbons; biogeochemistry and microbial diversity will be also undertaken on the mats subjected to hydrocarbon pollution.
Community level (Work package 2): Mesocosm studies of the biodegradation of selected hydrocarbon molecules will be carried out on a controlled microbial mat using biogeochemistry methods and molecular genetics to determine biodiversity.
Organismic level (Work package 3): The microbial diversity and the physiology will be carried out on isolated micro organisms of ecological importance in microbial mats subjected to oil pollution and particularly protozoa, cyanobacteria, anoxygenic phototropic bacteria, sulphate-reducing bacteria, denitrifying bacteria, aerobic, microaerophilic and fermentative bacteria. The degradation of some selected hydrocarbons by the isolated micro organisms will be investigated by chemical analyses.
Sub-cellular level (Work package 4): The metabolic pathways of hydrocarbon degradation in selected micro organisms will be analysed via the biochemistry of oxygenises in aerobic metabolism and biochemistry of anaerobic enzymes.
EXPECTED IMPACTS
The primary aim of this research programme is to evaluate the potential of using microbial mats as a means of restoring oil contaminated sites to their original pristine state without the excessive use of dispersants and extensive change in the character of the coastal landscape. The ability to exploit and use naturally occurring microbial communities such as those present in microbial mats to degrade pollutants like crude oil is of major significance in the effective management and maintenance of pristine marine habitats such as estuaries, deltas and sandy beaches. The gained technology that will arise from this project can be employed to develop effective management strategies for the bioremediation of these fragile ecosystems. The development of methods or new techniques and new approaches to microbial mats can be transferred to training and educational institutions for a better knowledge of coastal zone conservation and management. Microbial mats may be used to seed 'raceways' designed to promote the growth of controlled microbial mat communities. These mats would be 'conditioned' by exposure to increasing concentrations of selected hydrocarbons. Oil-contaminated seawater would then be circulated through the system until the oil had been degraded and the clean water returned to the sea. This approach, unlike previously developed methods, has the advantage that it does not involve the 'seeding' of oil-spills with microbial inocula or oleophilic nutrients. This technology is particularly targeted at the bioremediation of sites where limited volumes of seawater are contaminated by high concentrations of hydrocarbons and/or crude oil. This approach is unlike other methods used for bioremediation in the marine environment where pollutant-degrading bacteria are released to ocean or coastal sediments. We propose to use an entire microbial community rather than a selected single strain, which allows the biodegradation of the various components of crude oil simultaneously by a large spectrum of bacteria operating in concert.
At the stage of our investigations, after three years of running the project, we can bring information on the functioning of the different investigated ecosystems and the general effect of petroleum amendment. Biological degradation of oil components under oxic conditions in mats is intense: when the microbial mats in coastal zones are fully covered by oil, they react by growing above the oil after few weeks of exposure. The filamentous gliding cyanobacteria grow through the layer of oil up to the surface and form a new bacterial layer above the oil. Thus the oil is trapped like "sandwich" between an oxic layer of bacteria above and an anoxic layer of bacteria below. This situation is favorable for a better biodegradation and for an isolation of the oil, trapped in the matrix of the microbial mat, thus eliminated from the surrounding environment. Mat systems from pristine environments change their community structure significantly upon contact with petroleum hydrocarbons and then form a matrix for a developing oil-degrading community: the cyanobacteria produces exopolysaccharides that form a matrix and act in bioemulsification of the oil. The aerobic bacteria degrading oil are more active in the matrix for the availability of oil components and due to high oxygen production by Cyanobacteria. In the mat, several bacterial types are selected mainly the aerobic genus Marinobacter and some sulfate-reducing bacteria. Biological degradation of oil components under anoxic conditions in mat systems is slow and presumably highly selective, but influences the sulfur chemistry (sulfide formation, growth of sulfur oxidizing bacteria) of the mats: in the anoxic layers below the oil, sulfate-reducing bacteria are more efficient when they are cohabiting with purple sulfur bacteria, for a better but still low biodegradation.

The interactions between aerobic and anaerobic bacteria and processes at the microoxic/anoxic interface are more efficient for a good biodegradation: several molecules could by efficiently biodegraded including linear and ramified alcanes (hexadecane and pristane), polyaromatic compounds up to 3 aromatic cycles, sulfur compounds (dibenzothiophene). These molecules could be degraded even in aerobic conditions mainly by bacteria of the genus Marinobacter, and anaerobically with sulfate-reducing bacteria and denitrifying bacteria. This last process is very low however. Cyanobacteria are important structural elements in mats, even though their role in a direct biochemical attack of oil hydrocarbons is still unclear. In conclusion, the cooperation between the different bacterial groups in the microbial mats is more efficient that the isolated bacteria for the biodegradation of the oil components that are trapped in the matrix of the cyanobacteria. Thus, microbial mats that develop along the coastal zones should be protected and maintained for their capacities of bioremediation.

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CSC - Cost-sharing contracts

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UNIVERSITÉ DE PAU ET DES PAYS DE L'ADOUR
Contributo UE
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Indirizzo
Avenue de l'Université
64000 PAU
Francia

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Ultimo aggiornamento: 28 Luglio 2005

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Permalink: https://cordis.europa.eu/project/id/EVK3-CT-1999-00010/it

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