Biology subjects

Fernandez-Juarez, V.

Publications and source records attributed to Fernandez-Juarez, V..

3 recordsLinked to original sources

bioRxiv2021

Cell size matters: nano- and micro-plastics preferentially drive declines of large marine phytoplankton due to co-aggregation

Marine plastic pollution represents a key environmental concern. Whilst ecotoxicological data for plastic is increasingly available, its impact upon marine phytoplankton remains unclear. Owing to their predicted abundance in the marine environment and likely interactions with phytoplankton, here we focus on the smaller fraction of plastic particles ([~]50 nm and [~]2 {micro}m polystyrene spheres). Exposure of natural phytoplankton communities and laboratory cultures revealed that plastic exposure does not follow traditional trends in ecotoxicological research, since large phytoplankton appear particularly susceptible towards plastics exposure despite their higher surface-to-volume ratios. Cell declines appear driven by hetero-aggregation and co-sedimentation of cells with plastic particles, recorded visually and demonstrated using confocal microscopy. As a consequence, plastic exposure also caused disruption to photosynthetic functioning, as determined by both photosynthetic efficiency and high throughput proteomics. Negative effects upon phytoplankton are recorded at concentrations orders of magnitude above those estimated in the environment. Hence, it is likely that impacts of NPs and MPs are exacerbated at the high concentrations typically used in ecotoxicological research (i.e., mg L-1).

ecology↗

bioRxiv2021

Response of Posidonia oceanica (L.) Delile and its associated N2 fixers to different combinations of temperature and light levels

Ocean warming and water turbidity are threats for the persistence of seagrass meadows and their effects on the productivity of seagrasses and the functioning of their associated microorganisms have not been studied extensively. The purpose of this study was to assess the effects of different light levels and temperatures on Posidonia oceanica, the endemic seagrass species in the Mediterranean Sea, and their N2 fixing community, which contributes importantly to the nitrogen requirements and high productivity of the plants. Aquarium experiments were conducted in winter when the plants are more vulnerable to changes in temperature, subjecting them to short-term exposures to ambient (15.5 {degrees}C) and elevated temperatures (ambient+5.5 {degrees}C) and at limited (13 mol photons m-2 s-1) and saturating light conditions (124 mol photons m-2 s-1). Primary production, chlorophyll content, reactive oxygen species production, polyphenols content, the nifH gene expression, N2 fixation and alkaline phosphatase activities were measured in different plant tissues. Plants incubated at ambient temperature and high light exhibited enhanced total chlorophyll production and significantly higher gross and net primary production, which were approximately two-fold compared to the rest of the treatments. The oxidative stress analyses revealed increased production of reactive oxygen species in young leaves incubated at ambient temperature and saturating light, while the polyphenols content in top leaves was considerably higher under elevated temperatures. In contrast, N2 fixation and alkaline phosphatase rates were significantly higher under elevated temperature and low light levels. The presence of the N2 fixing phylotypes UCYN-A, -B and -C was detected through genetic analyses, with UCYN-B demonstrating the highest nifH gene transcription levels at elevated temperatures. These findings emphasize the significant role of irradiance on the productivity of P. oceanica and the temperature dependence of the N2 fixation process in winter.

ecology↗

bioRxiv2020

"The good, the bad and the double-sword" effects of exposure to MPs and their organic additives on N2-fixing bacteria

The accumulation of microplastics (MPs) pollution at depths suggests the susceptibility of benthic organisms (e.g. seagrasses and their associated macro- and micro-organisms) to the effects of these pollutants. Little is known about the direct effects of MPs and their organic additives on marine bacteria, e.g. in one of the most ecologically significant groups, the diazotrophs or N2-fixing bacteria. To fill this gap of knowledge, we exposed marine diazotrophs found in association with the endemic Mediterranean seagrass Posidonia oceanica to pure MPs which differ in physical properties (e.g. density, hydrophobicity and/or size), namely, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polystyrene (PS) and to their most abundant associated organic additives (e.g. fluoranthene, 1,2,5,6,9,10-hexabromocyclododecane [HBCD] and dioctyl-phthalate [DEHP]). Growth, protein overexpression, direct physical interactions between MPs and bacteria, phosphorus (P) acquisition mechanisms and N2-fixation rates were evaluated. Our results show species-specific responses of the autotrophic and heterotrophic N2-fixing bacteria tested and the responses were dependent on the type and concentration of MPs and additives. N2-fixing cyanobacteria were positively affected by environmental and high concentrations of MPs (e.g. PVC), as opposed to heterotrophic strains, that were only positively affected with high concentrations of [~]120 {micro}m-size MPs (detecting the overexpression of proteins related to plastic degradation and C-transport), and negatively affected by 1 {micro}m-size PS beads. Generally, the organic additives (e.g. fluoranthene) had a deleterious effect in both autotrophic and heterotrophic N2-fixing bacteria and the magnitude of the effect is suggested to be dependent on bacterial size. We did not find evidences that specific N2-fixation rates were significantly affected by exposure to MPs, albeit changes in bacterial abundance can affect the bulk N2-fixation rates. In summary, we reported for the first time, the beneficial (the "good"), deleterious (the "bad") and/or both (the "double-sword") effects of exposure to MPs and their organic additives on diazotrophs found in association with seagrasses.

microbiology↗