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- Structural modification of the Pseudomonas aeruginosa alkylquinoline cell–cell communication signal, HHQ, leads to benzofuranoquinolines with anti-virulence behaviour in ESKAPE pathogensPublication . ROSSETTO, VERONICA; Moore-Machacek, Ay'sha; Woods, David F.; Galvão, Helena M.; Shanahan, Rachel M.; Hickey, Aobha; O’Leary, Niall; O’Gara, Fergal; McGlacken, Gerard P.; Reen, F. JerryMicrobial populations have evolved intricate networks of negotiation and communication through which they can coexist in natural and host ecosystems. The nature of these systems can be complex and they are, for the most part, poorly understood at the polymicrobial level. The Pseudomonas Quinolone Signal (PQS) and its precursor 4- hydroxy- 2-heptylquinoline (HHQ) are signal molecules produced by the important nosocomial pathogen Pseudomonas aeruginosa. They are known to modulate the behaviour of co-colonizing bacterial and fungal pathogens such as Bacillus atropheaus, Candida albicans and Aspergillus fumigatus. While the structural basis for alkyl-quinolone signalling within P. aeruginosa has been studied extensively, less is known about how structural derivatives of these molecules can influ-ence multicellular behaviour and population- level decision-making in other co-colonizing organisms. In this study, we investigated a suite of small molecules derived initially from the HHQ framework, for anti-virulence activity against ESKAPE pathogens, at the species and strain levels. Somewhat surprisingly, with appropriate substitution, loss of the alkyl chain (present in HHQ and PQS) did not result in a loss of activity, presenting a more easily accessible synthetic framework for investigation. Virulence profiling uncovered significant levels of inter-strain variation among the responses of clinical and environmental isolates to small-molecule challenge. While several lead compounds were identified in this study, further work is needed to appreciate the extent of strain- level tolerance to small-molecule anti-infectives among pathogenic organisms.
- Tidal variability of phytoplankton and their environmental drivers in the freshwater reaches of the Guadiana estuary (SW Iberia)Publication . Domingues, Rita B.; Anselmo, Tânia P.; Barbosa, Ana B.; Sommer, Ulrich; Galvão, Helena M.The effects of different phases of semidiurnal and spring-neap tidal cycles on phytoplankton and environmental drivers were evaluated in a tidal, freshwater location of a mesotidal estuary (Guadiana estuary, SW Iberia). An Eulerian approach was used and sampling covered different seasons during 2008. Samples were collected during spring and neap tides, at high tide, mid-ebb, low tide and mid-flood. Several physical-chemical variables were measured, as well as phytoplankton abundance and biomass. Salinity was higher at high-tide and suspended particulate matter was higher during spring tides and flood, due to higher vertical mixing and resuspension of bottom sediments. Chlorophyll a concentration during winter and summer neap tides was higher than during spring tides, whilst the abundance of pennate diatoms was higher during winter and Spring spring tides than during neap tides, probably reflecting differences in river discharge. Overall, tidally-induced differences detected in the freshwater tidal reaches of the Guadiana estuary were not as considerable as those observed in the lower estuary. However, the occurrence of tidally-induced variability in some seasons reflects that thorough sampling programs to study estuarine tidal dynamics should be conducted throughout the year. Occasional sampling will not reflect the typical variability of these highly dynamic systems.
- Light as a driver of phytoplankton growth and production in the freshwater tidal zone of a turbid estuaryPublication . Domingues, Rita B.; Anselmo, Tânia P.; Barbosa, Ana B.; Sommer, Ulrich; Galvão, Helena M.Light is usually the main driver of phytoplankton growth in turbid estuaries, but it has received far less attention than nutrients as a bottom-up factor. This study presents the first experimental analysis of light limitation of phytoplankton growth and production and its seasonal variability in the freshwater tidal reaches of the turbid Guadiana estuary, SE Portugal/SW Spain. Natural phytoplankton communities were exposed to different photosynthetically active radiation (PAR) intensities. Short-term incubations with addition of 14HCO3 were used to estimate photosynthetic parameters and long-term incubations allowed the evaluation of the effects of light on phytoplankton composition and growth. Light limitation of phytoplankton growth occurred throughout the year in the freshwater tidal reaches of the estuary and no photoinhibition was observed at least up to 615 mmol photonsm 2 s 1. In the summer, co-limitation by nutrients prevented a positive response of phytoplankton to light enrichment. Diatoms were the most light-limited group, whilst cyanobacteria were the only group acclimated to low-light conditions. Green algae and dinoflagellates responded positively to higher PAR exposures. High saturating irradiances, high light-saturated rates of primary production and low photosynthetic efficiencies suggest that phytoplankton community was not acclimated to the low-light conditions that prevail in the Guadiana estuary.
- Nutrient limitation of phytoplankton growth in the freshwater tidal zone of a turbid, Mediterranean estuaryPublication . Domingues, Rita B.; Anselmo, Tânia P.; Barbosa, Ana B.; Sommer, Ulrich; Galvão, Helena M.Identification of the limiting nutrient(s) is a requirement for the rational management of eutrophication. Here, we present the first experimental analysis of nutrient limitation of phytoplankton growth and its seasonal variation in the Guadiana estuary (SE Portugal-SW Spain). Ten microcosm experiments were performed during 2005 and 2008, using water samples collected in the freshwater tidal zone of the Guadiana estuary. Nitrate, phosphate and silicate were added in a single pulse, alone and in combinations. Experimental treatments were incubated for 4 days under controlled laboratory conditions. Phytoplankton response to nutrient enrichment was evaluated through changes in biomass (Chla), and abundance of specific phytoplankton groups. Overall, phytoplankton growth seemed to be nitrogen-limited throughout the productive period, especially green algae in 2005 and diatoms in 2008. In the summer 2008, cyanobacteria and the harmful dinoflagellate Kryptoperidinium foliaceum responded to N enrichment in the absence of Si. Indeed, the presence of K. foliaceum was observed for the first time in the freshwater tidal reaches of the Guadiana estuary, where dinoflagellates were usually absent or rare. The significant increase on dinoflagellates and cyanobacteria growth in response to N enrichment in the absence of Si is alarming, because anthropogenic nutrient enrichments usually increase N and P, but not Si. Furthermore, relatively high N concentrations, up to 22 mM, were found to be limiting to phytoplankton growth. These results should therefore be used as a management tool when establishing nutrient criteria and nutrient loading budgets to estuarine waters.
- A importância do mundo invisível dos micróbios na Ria FormosaPublication . Mendes, Pedro; Galvão, Helena; Caetano, Sandra; Icely, John; Newton, AliceCom o desenvolvimento da microscopia de epifluorescência e técnicas sensíveis de radioisótopos na década de 1970, a abundância e atividade de microrganismos pôde ser observada e estudada em águas marinhas. Estas observações resultaram num novo conceito de rápida transferência e reciclagem de matéria orgânica através de um ciclo microbiano, o “microbial loop”.
- Role of microbes in the Ria Formosa lagoonPublication . Galvão, Helena M.; Mendes, Pedro; Caetano, Sandra; Icely, John; Newton, AliceWith the development of epifluorescence microscopy and sensitive radioisotope techniques, high abundance and activity of microorganisms was observed in marine waters since 1970s and 1980s. These observations resulted in a new concept of rapid turn-over and recycling of organic matter through a ‘microbial loop’ (Azam et al., 1983; Azam, 1998). Figure 5.1 illustrates fluxes of material through the marine microbial loop. Main processes are C fixation by photosynthetic microorganisms (prokaryotic and eukaryotic) with exudation losses of Dissolved Organic Matter (DOM), which is incorporated by heterotrophic bacteria. Phagotrophic protists in turn graze both autotrophs and bacteria producing ‘sloppy feeding’ loss of DOM, which returns to the loop. DOM is remineralized by all microorganisms into Dissolved Inorganic Nutrients (DIN), which are taken up by autotrophic and heterotrophic microorganisms.
- Short-term effects of climate change on Planktonic Heterotrophic Prokaryotes in a temperate Coastal Lagoon: Temperature Is good, ultraviolet radiation Is bad, and CO2 Is neutralPublication . B. Barbosa, Ana; Mosley, Benjamin A.; M. Galvão, Helena; Domingues, Rita B.Planktonic heterotrophic prokaryotes (HProks) are a pivotal functional group in marine ecosystems and are highly sensitive to environmental variability and climate change. This study aimed to investigate the short-term effects of increasing carbon dioxide (CO2), ultraviolet radiation (UVR), and temperature on natural assemblages of HProks in the Ria Formosa coastal lagoon during winter. Two multi-stressor microcosm experiments were used to evaluate the isolated and combined effects of these environmental changes on HProk abundance, production, growth, and mortality rates. The isolated and combined effects of increased CO2 on HProks were not significant. However, HProk production, cellular activity, instantaneous growth rate, and mortality rate were negatively influenced by elevated UVR and positively influenced by warming. Stronger effects were detected on HProk mortality in relation to specific growth rate, leading to higher HProk net growth rates and abundance under elevated UVR and lower values under warming conditions.
- Role of transient silicon limitation in the development of cyanobacteria blooms in the Guadiana estuary, south-western IberiaPublication . Rocha, C.; Galvão, Helena M.; Barbosa, Ana B.The Guadiana estuary, located between Portugal and Spain, has the fourth largest drainage basin of Iberian river systems. Up to 75% of the catchment area has been regulated by dams since the early 1970s. During the 1980s and 1990s, an increasing occurrence of summer cyanobacteria blooms dominated by the potentially toxic Microcystis spp. was reported. In an effort to understand the causes of recurrent noxious blooms in the Guadiana estuary, nutrients (phosphorus, nitrogen [nitrate, nitrite and ammonium], and silicon [silicic acid], chlorophyll a and phytoplankton abundance, specific composition and biomass were evaluated during field surveys, from April 1997 to March 1998. A pattern of successive blooms of different phytoplankton assemblages was observed throughout this period. Diatoms (nano-sized, chain-forming) dominated an early spring bloom (max. 18 × 103 cells ml–1) in March and April. Following the decrease in diatom abundance, a chlorophyte bloom (max. 11 × 103 cells ml–1) and then a cyanobacteria bloom (>6 × 104 cells ml–1) quickly followed during late spring through to early summer. From July to September, a major cyanobacteria bloom dominated by the potentially toxic Microcystis spp. (> 4 × 105 cells ml–1) developed in the freshwater zone. The results indicate that high winter loads of nitrogen and phosphorus led to the depletion of silicate (down to as low as 0.2 μM) during the early spring diatom bloom, which conditioned the successive phytoplankton assemblages during the remaining productive period. Low monthly discharge rates during spring and summer further provided an environment with low Si:N and N:P relative availability which, coupled with high water-column temperature (>21°C), seemed to favour the dominance of cyanobacteria over chlorophytes during the summer.
- Connections between upwelling patterns and phytoplankton variability under different coastal regimes in SW Iberia PeninsulaPublication . Krug, Lilian; Silvano, Kathleen M.; Barbosa, Ana B.; Domingues, Rita B.; Galvão, Helena M.; Luis, Joaquim; Platt, Trevor; Relvas, Paulo; Sathyendranath, ShubhaThe region off southwestern Iberia (NE Atlantic) encompasses a wide variety of oceanographic regimes, including differently (geographic) oriented coastal areas impacted by upwelling, riverine inputs and submarine groundwater discharge, submarine canyons and seamounts, and open ocean waters, thereby potentially promoting zone-specific phytoplankton dynamics. Overall, this heterogeneous region is classified as being very sensitive to climate change, and climate-driven alterations (e.g., sea surface warming, changes in upwelling patterns and intensity) have been recently reported for the area. The present study aims to understand the contribution of upwelling to seasonal and interannual variability of coastal phytoplankton, using a remote sensing-based approach. Phytoplankton variability was evaluated using satellite-derived chlorophyll-a (Chl-a), as a proxy for phytoplankton biomass, and primary productivity (PP). Chl-a were obtained from merged SeaWiFS (Seaviewing Wide Field-of-view Sensor), MeRIS (Medium Resolution Imaging Spectrometer) and MODIS-Aqua (Moderate-resolution Imaging Spectroradiometer) sensors at Globcolour portal. PP data at 9.25 km resolution were derived from Eppley’s Vertically Generalized Production Model, based on SeaWiFS and MODIS-Aqua and available at the Ocean Productivity site. Upwelling intensity was estimated using the difference in sea surface temperature (SST) between off and nearshore zones. Advanced Very-High Resolution Radiometer (AVHRR) 4 km SST were obtained from Pathfinder database. Other phytoplankton environmental drivers, such as local (e.g., river flow) and global (e.g., North Atlantic Oscillation - NAO) climate variables, were also analysed. The study area was divided into subareas differently impacted by upwelling and riverine flow, and satellitederived data was averaged for each zone. Seasonal and interannual variability covering a 14-year time series (1998- 2011) for each variable/region were explored. Chl-a at offshelf locations was significantly lower than coastal areas, and exhibited a fairly stable unimodal annual cycle, with maximum during March. Coastal locations displayed more variable annual patterns, with spring and summer Chl-a maxima, reflecting the impact of upwelling events and freshwater inputs. In respect to interannual variability, NAO index and coastal Chl-a were negative and significantly correlated, with 1-month lag. Chl-a interannual trends were also correlated to local climate variables, namely riverine flow for the easternmost coastal zone. The correlation between upwelling intensity and phytoplankton off SW Iberia is region-dependent being less strong within regions dominated by riverine influence.
- Status of the Guadiana estuary (South Portugal) during 1996-1998: an ecohydrological approachPublication . Teodosio, Maria; Chícharo, Luís; Galvão, Helena M.; Barbosa, Ana B.; Marques, M. Helena; Andrade, José Pedro; Esteves, E.; Miguel, Cláudia; Gouveia, IsabelThe aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary (1996–1998) before the construction of the Alqueva dam. This work was carried out to determine how environmental factors affect seasonal and tidal variations of plankton populations in the estuary. The available information on the subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated into a geographic information system-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. River flow near Mértola (ca 50 km upstream from the mouth) reached 3400×106 m3 in winter and decreased to 42×106 m3 in summer. With respect to nutrients, nitrogen to phosphorus ratios indicated some limitation by phosphorus, except at the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may significantly influence the retention of zooplankton in the estuary. The fish larval life cycle, especially sensitive to environmental alterations, showed high ratios of ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was concluded that an ecohydrological approach, allowing integration of different elements from the cellular to the habitat level into a geographic information system, can contribute to a better understanding of the processes that influence the aquatic biota of the estuary. The approach will be a useful assessment tool for monitoring the estuary following dam completion.
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