Hugo Ribeiro

Bacterial community response to petroleum contamination and nutrient addition in sediments from a temperate salt marsh.

Microbial communities play an important role in the biodegradation of organic pollutants in sediments, including hydrocarbons. The aim of this study was to evaluate the response of temperate salt marsh microbial communities to petroleum contamination, in terms of community structure, abundance and capacity to degrade hydrocarbons. Sediments un-colonized and colonized (rhizosediments) by Juncus maritimus, Phragmites australis and Triglochin striata were collected in a temperate estuary (Lima, NW Portugal), spiked with petroleum under variable nutritional conditions, and incubated for 15 days. Results showed that plant speciation emerged as the major factor for shaping the rhizosphere community structure, overriding the petroleum influence. Moreover, when exposed to petroleum contamination, the distinct salt marsh microbial communities responded similarly with (i) increased abundance, (ii) changes in structure, and (iii) decreased diversity. Communities, particularly those associated to J. maritimus and P. australis roots displayed a potential to degrade petroleum hydrocarbons, with degradation percentages between 15% and 41%, depending on sediment type and nutritional conditions. In conclusion, distinct salt marsh microbial communities responded similarly to petroleum contamination, but presented different pace, nutritional requirements, and potential for its biodegradation, which should be taken into account when developing bioremediation strategies.

INFLUENCE OF DIFFERENT SALT MARSH PLANTS ON HYDROCARBON DEGRADING MICROORGANISMS ABUNDANCE THROUGHOUT A PHENOLOGICAL CYCLE

The influence of Juncus maritimus, Phragmites australis, and Triglochin striata on hydrocarbon degrading microorganisms (HD) in Lima River estuary (NW Portugal) was investigated through a year-long plant life cycle. Sediments un-colonized and colonized (rhizosediments) by those salt marsh plants were sampled for HD, total cell counts (TCC), and total petroleum hydrocarbons (TPHs) assessment. Generally, TCC seemed to be markedly thriving by the presence of roots, but without significant (p > 0.05) differences among rhizosediments. Nevertheless, plants seemed to have a distinct influence on HD abundance, particularly during the flowering season, with higher HD abundance in the rhizosediments of the fibrous roots plants (J. maritimus <P. australis <T. striata). Our data suggest that different plants have distinct influence on the dynamics of HD populations within its own rhizosphere, particularly during the flowering season, suggesting a period of higher rhizoremediation activity. Additionally, during the vegetative period, plants with fibrous and dense root system tend to retain hydrocarbons around their belowground tissues more efficiently than plants with adventitious root system. Overall results indicate that fibrous root plants have a higher potential to promote hydrocarbons degradation, and that seasonality should be taken into account when designing long-term rhizoremediation strategies in estuarine areas.

Salt marsh sediment characteristics as key regulators on the efficiency of hydrocarbons bioremediation by Juncus maritimus rhizospheric bacterial community

Mitigation of petroleum hydrocarbons was investigated during a 5-month greenhouse experiment, to assess the rhizoremediation (RR) potential in sediments with different characteristics colonized by Juncus maritimus, a salt marsh plant commonly found in temperate estuaries. Furthermore, the efficiency of two bioremediation treatments namely biostimulation (BS) by the addition of nutrients, and bioaugmentation (BA) by addition of indigenous microorganisms, was tested in combination with RR. The effect of the distinct treatments on hydrocarbon degradation, root biomass weight, and bacterial community structure was assessed. Our result showed higher potential for hydrocarbon degradation (evaluated by total petroleum hydrocarbon analysis) in coarse rhizosediments with low organic matter (OM), than rhizosediments with high OM, and small size particles. Moreover, the bacterial community structure was shaped according to the rhizosediment characteristics, highlighting the importance of specific microbe-particle associations to define the structure of rhizospheric bacterial communities, rather than external factors, such as hydrocarbon contamination or the applied treatments. The potential for hydrocarbon RR seems to depend on root system development and bacterial diversity, since biodegradation efficiencies were positively related with these two parameters. Treatments with higher root biomass, and concomitantly with higher bacterial diversity yielded higher hydrocarbon degradation. Moreover, BS and BA did not enhance hydrocarbons RR. In fact, it was observed that higher nutrient availability might interfere with root growth and negatively influence hydrocarbon degradation performance. Therefore, our results suggested that to conduct appropriate hydrocarbon bioremediation strategies, the effect of sediment characteristics on root growth/exploration should be taken into consideration, a feature not explored in previous studies. Furthermore, strategies aiming for the recovery of bacterial diversity after oil spills may improve the efficiency of hydrocarbon biodegradation in contaminated salt marsh sediments.

Potential of dissimilatory nitrate reduction pathways in polycyclic aromatic hydrocarbon degradation

This study investigates the potential of an indigenous estuarine microbial consortium to degrade two polycyclic aromatic hydrocarbons (PAHs), naphthalene and fluoranthene, under nitrate-reducing conditions. Two physicochemically diverse sediment samples from the Lima Estuary (Portugal) were spiked individually with 25 mg L-1 of each PAH in laboratory designed microcosms. Sediments without PAHs and autoclaved sediments spiked with PAHs were run in parallel. Destructive sampling at the beginning and after 3, 6, 12, 30 and 63 weeks incubation was performed. Naphthalene and fluoranthene levels decreased over time with distinct degradation dynamics varying with sediment type. Next-generation sequencing (NGS) of 16 S rRNA gene amplicons revealed that the sediment type and incubation time were the main drivers influencing the microbial community structure rather than the impact of PAH amendments. Predicted microbial functional analyses revealed clear shifts and interrelationships between genes involved in anaerobic and aerobic degradation of PAHs and in the dissimilatory nitrate-reducing pathways (denitrification and dissimilatory nitrate reduction to ammonium - DNRA). These findings reinforced by clear biogeochemical denitrification signals (NO3- consumption, and NH4+ increased during the incubation period), suggest that naphthalene and fluoranthene degradation may be coupled with denitrification and DNRA metabolism. The results of this study contribute to the understanding of the dissimilatory nitrate-reducing pathways and help uncover their involvement in degradation of PAHs, which will be crucial for directing remediation strategies of PAH-contaminated anoxic sediments.

Salt Marsh Plants’ Potential for the Remediation of Hydrocarbon-Contaminated Environments

Petroleum contamination can cause serious damage to ecosystems, and natural biological processes may be convenient alternatives to minimise ecological impacts. However, these are long processes, and approaches to accelerate them are needed. In this chapter two studies carried out to ascertain the phytoremediation potential of salt marsh plants for the remediation of hydrocarbon-contaminated environments in near-natural controlled conditions are reported. In the first study, the suitability of Juncus maritimus and Phragmites australis for rhizodegradation of petroleum hydrocarbon-contaminated estuarine sediment, the medium where the plants grow, was assessed. The second study involved soil contaminated with petrochemical products and evaluated the capability of Halimione portulacoides, Juncus maritimus and Scirpus maritimus for soil remediation. Results indicate that salt marsh plants, or salt-tolerant marsh plants, can have an important role in the restoration and remediation of not only hydrocarbon-contaminated sediments but also hydrocarbon-contaminated nonsaline soils. However, the specificities of the plant species, the environmental conditions and the time frame should be well thought out when engaging a revegetation of hydrocarbon-polluted sites with these plants.

MarinEye — A tool for marine monitoring

This work presents an autonomous system for marine integrated physical-chemical and biological monitoring - the MarinEye system. It comprises a set of sensors providing diverse and relevant information for oceanic environment characterization and marine biology studies. It is constituted by a physical-chemical water properties sensor suite, a water filtration and sampling system for DNA collection, a plankton imaging system and biomass assessment acoustic system. The MarinEye system has onboard computational and logging capabilities allowing it either for autonomous operation or for integration in other marine observing systems (such as Observatories or robotic vehicles. It was designed in order to collect integrated multi-trophic monitoring data. The validation in operational environment on 3 marine observatories: RAIA, BerlengasWatch and Cascais on the coast of Portugal is also discussed.