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- Green roofs as a biotechnological solution to increase water retention in urban areasPublication . Monteiro, Cristina M.; Castro, Paula M. L.
- Metal uptake by microalgae: underlying mechanisms and practical applicationsPublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. XavierMetal contamination of a few aquatic, atmospheric, and soil ecosystems has increased ever since the industrial revolution, owing to discharge of such elements via the effluents of some industrial facilities. Their presence to excessive levels in the environment will eventually lead to serious health problems in higher animals owing to accumulation throughout the food web. Current physicochemical methods available for recovery of metal pollutants (e.g., chemical precipitation, oxidation/reduction, or physical ion exchange) are either expensive or inefficient when they are present at very low concentrations. Consequently, removal of toxic metals by microorganisms has emerged as a potentially more economical alternative. Microalgae (in terms of both living and nonliving biomass) are an example of microorganisms suitable to recover metals and able to attain noteworthy percent removals. Their relatively high metal-binding capacities arise from the intrinsic composition of their cell walls, which contain negatively charged functional groups. Consequently, microalgal cells are particularly efficient in uptake of those contaminants when at low levels. Self-defense mechanisms developed by microalgal cells to survive in metal-containing media and environmental factors that affect their removal (e.g., pH, temperature, and biomass concentration) are reviewed here in a comprehensive way and further discussed in attempts to rationalize this form of remediation vis-a-vis with conventional nonbiological alternatives
- Aproveitamento de águas pluviais em edifícios com coberturas verdesPublication . Monteiro, Cristina M.; Castro, Paula M. L.
- Substrate influence on aromatic plant growth in extensive green roofs in a Mediterranean climatePublication . Monteiro, Cristina M.; Calheiros, Cristina S. C.; Martins, João P.; Costa, Francisco M.; Palha, Paulo; Freitas, Sara de; Ramos, Nuno M. M.; Castro, Paula M. L.Green roofs have been described as technical solutions to overcome urban environmental problems, such as decrease of vegetation and stormwater management. In the present study, two pilot 20 m2 extensive green roofs were implemented in an urban Mediterranean region, at a 1st storey on a warehouse building structure, in order to test the adequacy of different substrates for supporting aromatic plants (Lavandula dentata, Helichrysum italicum, Satureja montana, Thymus caespititius and Thymus pseudolanuginosus). Experimental substrates included expanded clay and granulated cork as main components, supplemented with organic matter and crushed egg shell. A commercial substrate that obeys to FLL guidelines was also tested. Plant growth was assessed and compared within each platform. All experimental substrates proved to be adequate for vegetation growth, with the combination of 70% expanded clay, 15% organic matter and 15% crushed egg shell showing the best results regarding plant establishment and growth over time. Water runoff quality parameters - turbidity, pH, conductivity, NH4+, NO3−, PO43− - met standard values required for water reuse for non-potable purposes, such as toilet flushing or irrigation. Preliminary qualitative thermographic measurements comparing surface temperature of different plant species and the substrate showed that temperature of vegetation surface was lower than substrate, reinforcing green roofs benefits of lowering air temperature in their surroundings. The present research shows that aromatic vegetation combined with clay substrates are suitable for green roofs located in countries of the Mediterranean region.
- Modelling growth of, and removal of Zn and Hg by a wild microalgal consortiumPublication . Monteiro, Cristina M.; Brandão, Teresa R. S.; Castro, Paula M. L.; Malcata, F. XavierMicroorganisms isolated from sites contaminated with heavy metals usually possess a higher removal capacity than strains from regular cultures. Heavy metal-containing soil samples from an industrial dumpsite in Northern Portugal were accordingly collected; following enrichment under metal stress, a consortium of wild microalgae was obtained. Their ability to grow in the presence of, and their capacity to recover heavy metals was comprehensively studied; the datasets thus generated were fitted to by a combined model of biomass growth and metal uptake, derived from first principles. After exposure to 15 and 25 mg/L Zn2+ for 6 days, the microalgal consortium reached similar, or higher cell density than the control; however, under 50 and 65 mg/L Zn2+, 71% to 84% inhibition was observed. Growth in the presence of Hg2+ was significantly inhibited, even at a concentration as low as 25 μg/L, and 90% inhibition was observed above 100 μg/L. The maximum amount of Zn2+ removed was 21.3 mg/L, upon exposure to 25 mg/L for 6 day, whereas the maximum removal of Hg2+ was 335 μg/L, upon 6 day in the presence of 350 ug/L. The aforementioned mechanistic model was built upon Monod assumptions (including heavy metal inhibition), coupled with Leudeking–Piret relationships between the rates of biomass growth and metal removal. The overall fits were good under all experimental conditions tested, thus conveying a useful tool for rational optimisation of microalga-mediated bioremediation.
- Capacity of simultaneous removal of zinc and cadmium from contaminated media, by two microalgae isolated from a polluted sitePublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. XavierSeveral aquatic environments have been contaminated with heavy metals dumped via industrial effluents. Numerous studies have been published regarding the removal of single metals from aqueous solutions by microalgal biomass. However, such studies do not reflect the actual problem associated with industrial effluents because usually more than one metal species is present. Here we studied the biosorption capacity of Zn2+ and Cd2+ as single- and binary-metal systems by two microalgae, Scenedesmus obliquus and Desmodesmus pleiomorphus, isolated from a polluted site in Northern Portugal. For each metal independently, D. pleiomorphus showed a higher metal sorption capacity than S. obliquus, at concentrations ranging from 60 to 300 mg/l (except 150 mg(Cd)/l). Maximum amounts of Zn2+ and Cd2+ removed were 22.3 and 60.8 mg/g by S. obliquus, and 83.1 and 58.6 mg/g by D. pleiomorphus. In binary-metal solutions, S. obliquus was in general able to remove Zn2+ to higher extents than Cd2+, whereas the opposite was observed with D. pleiomorphus. The simultaneous uptake of Zn2+ and Cd2+ by both microalgae was considerably lower than that of their single-metal counterparts, at equivalent concentrations. Although microalgal uptake from binary-metal solutions was lower than from single-metal ones, the wild microalgae selected were able to efficiently take up mixtures of Zn2+ and Cd2+ up to 300 mg/l of both metals-thus materializing a promising bioremediation vector for polluted waters.
- Biosorption of zinc ions from aqueous solution by the microalga Scenedesmus obliquusPublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. XavierAquatic environments are often exposed to toxic heavy metals, which gain access to the food chain via microalgae and may cause severe problems at higher trophic levels. However, such a metabolic specificity can be taken advantage of in bioremediation strategies. The potential of a novel wild strain of Scenedesmus obliquus, previously isolated from a heavy metal-contaminated site in northern Portugal, to remove Zn from aqueous solutions was thus studied, using several initial concentrations. The removal extent reached its maximum by 1 day: 836.5 mg Zn/g biomass, at the initial concentration of 75 mg/L, mainly by adsorption onto the cell surface. Comparative studies encompassing a commercially available strain of the same microalgal species led to a maximum removal extent of only 429.6 mg Zn/g biomass, under identical conditions. Heat-inactivated cells permitted a maximum removal of 209.6 mg Zn/g biomass, at an initial concentration of 50 mg Zn/L. The maximum adsorption capacity of Zn, estimated via Langmuir's isotherm, was 330 mg Zn/g biomass. Finally, Zn removal was highest at pH 6.0-7.0. It was proven, for the first time, that such a wild microalga can uptake and adsorb Zn very efficiently, which unfolds a particularly good potential for bioremediation. Its performance is far better than similar (reference) species, especially near neutrality, and even following heat-treatment.
- Contributions to the design of rainwater harvesting systems in buildings with green roofs in a Mediterranean climatePublication . Monteiro, C. M.; Calheiros, C. S. C.; Pimentel-Rodrigues, C.; Silva-Afonso, A.; Castro, P. M. L.Green roofs (GRs) are becoming a trend in urban areas, favouring thermal performance of buildings, promoting removal of atmospheric pollutants, and acting as possible water collection spots. Rainwater harvesting systems in buildings can also contribute to the management of stormwater runoff reducing flood peaks. These technologies should be enhanced in Mediterranean countries where water scarcity is increasing and the occurrence of extreme events is becoming very significant, as a result of climate change. An extensive pilot GR with three aromatic plant species, Satureja montana, Thymus caespititius and Thymus pseudolanuginosus, designed to study several parameters affecting rainwater runoff, has been in operation for 12 months. Physico-chemical analyses of roof water runoff (turbidity, pH, conductivity, NH4(+), NO3(-), PO4(3-), chemical oxygen demand) have shown that water was of sufficient quality for non-potable uses in buildings, such as toilet flushing. An innovative approach allowed for the development of an expression to predict a 'monthly runoff coefficient' of the GR system. This parameter is essential when planning and designing GRs combined with rainwater harvesting systems in a Mediterranean climate. This study is a contribution to improving the basis for the design of rainwater harvesting systems in buildings with extensive GRs under a Mediterranean climate.
- Cadmium removal by two strains of desmodesmus pleiomorphus cellsPublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. XavierThe capacity of microalgae to accumulate heavy metals has been widely investigated for its potential applications in wastewater (bio)treatment. In this study, the ability of Desmodesmus pleiomorphus (strain L), a wild strain isolated from a polluted environment, to remove Cd from aqueous solutions was studied, by exposing its biomass to several Cd concentrations. Removal from solution reached a maximum of 61.2 mg Cd g−1 biomass by 1 day, at the highest initial supernatant concentration used (i.e., 5.0 mg Cd L−1), with most metal being adsorbed onto the cell surface. Metal removal by D. pleiomorphus (strain ACOI 561), a commercially available ecotype, was also assessed for comparative purposes; a removal of 76.4 mg Cd g−1 biomass was attained by 1 day for the same initial metal concentration. Assays for metal removal using thermally inactivated cells were also performed; the maximum removal extent observed was 47.1 mg Cd g−1 biomass, at the initial concentration of 5 mg Cd L−1. In experiments conducted at various pH values, the highest removal was achieved at pH 4.0. Both microalga strains proved their feasibility as biotechnological tools to remove Cd from aqueous solution.
- Endophytic culturable bacteria colonizing Lavandula dentata L. plants: Isolation, characterization and evaluation of their plant growth-promoting activitiesPublication . Pereira, S.I.A.; Monteiro, Cristina M.; Vega, A. L.; Castro, Paula M. L.Aromatic plants such as lavender are stirring the attention of many researchers due to their content in bioactive secondary metabolites that can be used in traditional medicine. However, information regarding naturally occurring lavender associated bacterial endophytes (BE) is limited. To the best of our knowledge, this is the first study which aims to assess the phylogenetic diversity of the culturable endophytic bacteria of Lavandula dentata cultivated under organic management and to evaluate their potential as plant growth promoting (PGP) agents. BE were grouped by random amplified polymorphic DNA and identified by 16S ribosomal RNA gene sequencing. Endophytes were further characterized for the ability to produce several PGP substances, like ammonia, siderophores, indol-3-acetic acid, and hydrogen cyanide and for the ability to solubilize phosphate. Plant cell-wall degrading enzymes were also determined. Densities of BE were higher in roots (log 6.39 CFU g−1 fresh weight) than in shoots (log 5.56 CFU g−1 fresh weight). Phylogenetic analysis showed that BE were affiliated to two major groups: -Proteobacteria (50%) and Firmicutes (31.6%) and a small part belonged to - (7.9%) and -Proteobacteria (10.5%), being Pseudomonas and Bacillus the most highly represented genera. Higher bacterial diversity was found in the lavender roots, with endophytes belonging to 6 different genera (Pseudomonas, Variovorax, Rhizobium, Caulobacter, Bacillus and Paenibacillus), than in shoots where only 3 genera (Bacillus, Pseudomonas and Xanthomonas) were found. Overall, BE showed ability to produce extracellular enzymes and multiple PGP traits, suggesting their potential use as efficient bioinoculants in sustainable cultivation of medicinal and aromatic plants.