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Marine microbial communities differ genetically, metabolically, and ecologically according to their lifestyle, and they may respond differently to environmental changes. In this study, we investigated the seasonal dynamics of bacterial assemblies in the free‐living (FL) and particle‐associated (PA) fractions across a span of 6 years in the Blanes Bay Microbial Observatory in the Northwestern Mediterranean. Both lifestyles showed marked seasonality. The trends in alpha diversity were similar, with lower values in spring–summer than in autumn‐winter. Samples from both fractions were grouped seasonally and the percentage of community variability explained by the measured environmental variables was comparable (32% in FL and 31% in PA). Canonical analyses showed that biotic interactions were determinants of bacterioplankton dynamics and that their relevance varies depending on lifestyles. Time‐decay curves confirmed a high degree of predictability in both fractions. Yet, 'seasonal' Amplicon Sequence Variants (ASVs) (as defined by Lomb Scargle time series analysis) in the PA communities represented 46% of the total relative abundance while these accounted for 30% in the FL fraction. These results demonstrate that bacteria inhabiting both fractions exhibit marked seasonality, highlighting the importance of accounting for both lifestyles to fully comprehend the dynamics of marine prokaryotic communities. [ABSTRACT FROM AUTHOR]

Estimation of prokaryotic growth rates is critical to understand the ecological role and contribution of different microbes to marine biogeochemical cycles. However, there is a general lack of knowledge on what factors control the growth rates of different prokaryotic groups and how these vary between sites and along seasons at a given site. We carried out several manipulation experiments during the four astronomical seasons in the coastal NW Mediterranean in order to evaluate the impact of grazing, viral mortality, resource competition and light on the growth and loss rates of prokaryotes. Gross and net growth rates of different bacterioplankton groups targeted by group-specific CARD-FISH probes and infrared microscopy (for aerobic anoxygenic phototrophs, AAP), were calculated from changes in cell abundances. Maximal group-specific growth rates were achieved when both predation pressure and nutrient limitation were experimentally minimized, while only a minimal effect of viral pressure on growth rates was observed; nevertheless, the response to predation removal was more remarkable in winter, when the bacterial community was not subjected to nutrient limitation. Although all groups showed increases in their growth rates when resource competition as well as grazers and viral pressure were reduced, Alteromonadaceae consistently presented the highest rates in all seasons. The response to light availability was generally weaker than that to the other factors, but it was variable between seasons. In summer and spring, the growth rates of AAP were stimulated by light whereas the growth of the SAR11 clade (likely containing proteorhodopsin) was enhanced by light in all seasons. Overall, our results set thresholds on bacterioplankton group-specific growth and mortality rates and contribute to estimate the seasonally changing contribution of various bacterioplankton groups to the function of microbial communities. Our results also indicate that the least abundant groups display the highest growth rates, contributing to the recycling of organic matter to a much greater extent than what their abundances alone would predict. [ABSTRACT FROM AUTHOR]

How much temporal recurrence is present in microbial assemblages is still an unanswered ecological question. Even though marked seasonal changes have been reported for whole microbial communities, less is known on the dynamics and seasonality of individual taxa. Here, we aim at understanding microbial recurrence at three different levels: community, taxonomic group and operational taxonomic units (OTUs). For that, we focused on a model microbial eukaryotic community populating a long‐term marine microbial observatory using 18S rRNA gene data from two organismal size fractions: the picoplankton (0.2–3 µm) and the nanoplankton (3–20 µm). We have developed an index to quantify recurrence in particular taxa. We found that community structure oscillated systematically between two main configurations corresponding to winter and summer over the 10 years studied. A few taxonomic groups such as Mamiellophyceae or MALV‐III presented clear recurrence (i.e., seasonality), whereas 13%–19% of the OTUs in both size fractions, accounting for ~40% of the relative abundance, featured recurrent dynamics. Altogether, our work links long‐term whole community dynamics with that of individual OTUs and taxonomic groups, indicating that recurrent and non‐recurrent changes characterize the dynamics of microbial assemblages. see also the Perspective by Moreira and López‐García [ABSTRACT FROM AUTHOR]

Biotic and abiotic particles shape the microspatial architecture that defines the microbial aquatic habitat, being particles highly variable in size and quality along oceanic horizontal and vertical gradients. We analysed the prokaryotic (bacterial and archaeal) diversity and community composition present in six distinct particle size classes ranging from the pico- to the microscale (0.2 to 200 μm). Further, we studied their variations along oceanographic horizontal (from the coast to open oceanic waters) and vertical (from the ocean surface into the meso- and bathypelagic ocean) gradients. In general, prokaryotic community composition was more variable with depth than in the transition from the coast to the open ocean. Comparing the six size-fractions, distinct prokaryotic communities were detected in each size-fraction, and whereas bacteria were more diverse in the larger size-fractions, archaea were more diverse in the smaller size-fractions. Comparison of prokaryotic community composition among particle size-fractions showed that most, but not all, taxonomic groups have a preference for a certain size-fraction sustained with depth. Species sorting, or the presence of diverse ecotypes with distinct size-fraction preferences, may explain why this trend is not conserved in all taxa. [ABSTRACT FROM AUTHOR]

Background: Microbial fuel cells (MFCs) operating with complex microbial communities have been extensively reported in the past, and are commonly used in applications such as wastewater treatment, bioremediation or in-situ powering of environmental sensors. However, our knowledge on how the composition of the microbial community and the different types of electron transfer to the anode affect the performance of these bioelectrochemical systems is far from complete. To fill this gap of knowledge, we designed a set of three MFCs with different constrains limiting direct and mediated electron transfer to the anode. Results: The results obtained indicate that MFCs with a naked anode on which a biofilm was allowed unrestricted development (MFC-A) had the most diverse archaeal and bacterial community, and offered the best performance. In this MFC both, direct and mediated electron transfer, occurred simultaneously, but direct electron transfer was the predominant mechanism. Microbial fuel cells in which the anode was enclosed in a dialysis membrane and biofilm was not allowed to develop (MFC-D), had a much lower power output (about 60% lower), and a prevalence of dissolved redox species that acted as putative electron shuttles. In the anolyte of this MFC, Arcobacter and Methanosaeta were the prevalent bacteria and archaea respectively. In the third MFC, in which the anode had been covered by a cation selective nafion membrane (MFC-N), power output decreased a further 5% (95% less than MFC-A). In this MFC, conventional organic electron shuttles could not operate and the low power output obtained was presumably attributed to fermentation end-products produced by some of the organisms present in the anolyte, probably Pseudomonas or Methanosaeta. Conclusion: Electron transfer mechanisms have an impact on the development of different microbial communities and in turn on MFC performance. Although a stable current was achieved in all cases, direct electron transfer MFC showed the best performance concluding that biofilms are the major contributors to current production in MFCs. Characterization of the complex microbial assemblages in these systems may help us to unveil new electrogenic microorganisms and improve our understanding on their role to the functioning of MFCs. [ABSTRACT FROM AUTHOR]

Abstract Agricultural practices have raised the level of nutrients reaching aquifers. In Europe, nitrate pollution is considered as one of the main threats for the quality of groundwater in agricultural areas. Treatment wetlands (TWs), also known as Constructed Wetlands, are used for groundwater treatment in areas with an important concentration of nitrogen compounds; total nitrogen removal depends on the type and operation scheme. Cork by-product from the industry has shown clear adsorbent properties to remove organic pollutants. The work is focused on the characterization of microbial communities involved in the nitrate‑nitrogen removal process in groundwater polluted from agricultural activities. The experimental design allowed the comparison of nitrate removal efficiency depending on the filter media material, cork by-product or gravel, used in two hybrid TWs (a vertical flow cell followed by a horizontal subsurface flow cell), installed in areas close to two irrigated agricultural plots at the Lleida plain area (Spain). Both physicochemical and microbial results were consistent and confirm the nitrate removal efficiency using cork as a filter media. A significant (p = 0.0025) higher removal in Bellvís TW using cork compared with the Vilanova de la Barca gravel system was observed, achieving a removal rate from 80 to 99% compared to the 5–46%, respectively. Regarding the community composition of the two different TWs, microorganisms were mainly related to the phylum Proteobacteria, and included members found to be key players in the nitrogen cycle, such as ammonia and nitrite oxidizers, as well as denitrifiers. Also, the group Bacteroidetes turns to be another abundant phylum from our bacterial dataset, whose members are suggested to be strongly involved in denitrification processes. Some groups showed to prevail depending on the type of media (cork or gravel); Firmicutes and Delta and Epsilonproteobacteria had a significant higher abundance in the TW with cork, while Acidobacteria and Planctomyces were prevalent in gravel. Therefore, cork could be an alternative material used by treatment wetlands to minimize the impact in the environment caused by nitrogen pollution in groundwater bodies. Graphical abstract Unlabelled Image Highlights • A higher nitrate removal efficiency (80-99%) using cork as substrate was observed. • Microbial community groups showed to prevail depending on the type of granular filter media. • The relative abundance of Firmicutes and Delta and Epsilonproteobacteria were significantly higher in the TW with cork. • The contribution of Acidobacteria and Planctomyces microorganism communities were superior in the TW with gravel • Cork treatment wetlands could be appropriate to treat nitrate polluted groundwater from agricultural activities. [ABSTRACT FROM AUTHOR]