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Aerosolization of soil-dust and organic aggregates in sea spray facilitates the long-range transport of bacteria, and likely viruses across the free atmosphere. Although long-distance transport occurs, there are many uncertainties associated with their deposition rates. Here, we demonstrate that even in pristine environments, above the atmospheric boundary layer, the downward flux of viruses ranged from 0.26 × 10 9 to >7 × 10 9  m -2 per day. These deposition rates were 9-461 times greater than the rates for bacteria, which ranged from 0.3 × 10 7 to >8 × 10 7  m -2 per day. The highest relative deposition rates for viruses were associated with atmospheric transport from marine rather than terrestrial sources. Deposition rates of bacteria were significantly higher during rain events and Saharan dust intrusions, whereas, rainfall did not significantly influence virus deposition. Virus deposition rates were positively correlated with organic aerosols <0.7 μm, whereas, bacteria were primarily associated with organic aerosols >0.7 μm, implying that viruses could have longer residence times in the atmosphere and, consequently, will be dispersed further. These results provide an explanation for enigmatic observations that viruses with very high genetic identity can be found in very distant and different environments.

The diversity of airborne microorganisms that potentially reach aquatic ecosystems during rain events is poorly explored. Here, we used a culture-independent approach to characterize bacterial assemblages during rain events with and without Saharan dust influence arriving to a high mountain lake in the Austrian Alps. Bacterial assemblage composition differed significantly between samples with and without Saharan dust influence. Although alpha diversity indices were within the same range in both sample categories, rain events with Atlantic or continental origins were dominated by Betaproteobacteria, whereas those with Saharan dust intrusions were dominated by Gammaproteobacteria. The high diversity and evenness observed in all samples suggests that different sources of bacteria contributed to the airborne assemblage collected at the lake shore. During experiments with bacterial assemblages collected during rain events with Saharan dust influence, cell numbers rapidly increased in sterile lake water from initially ∼3 × 103 cell ml-1 to 3.6-11.1 x105 cells ml-1 within 4-5 days, and initially, rare taxa dominated at the end of the experiment. Our study documents the dispersal of viable bacteria associated to Saharan dust intrusions travelling northwards as far as 47° latitude.

The study of transparent exopolymer particles (TEP) in the Mediterranean Sea is particularly relevant as they can be promoters of mucilage events, a frequent phenomenon there. We assessed the influence of bacterioplankton on TEP distribution and dynamics across the west-east axis of the Mediterranean Sea. We performed an extensive study of TEP, dissolved carbohydrates, and their relationships with bacterial abundance and bacterial production (BP). A significant and positive relationship was observed between BP and TEP in the study region (r (2) = 0.51, p < 0.001). The direct release of TEP by bacteria was experimentally corroborated using regrowth cultures where increases in TEP tracked bacterial growth in abundance and production. These TEP increases were positively related to the increases in BP (r (2) = 0.78, p < 0.05). The consistency (similar slopes) of the regression lines between BP and TEP in natural conditions and between the increases of BP and TEP in the experiments underlines the relevant role of bacteria in the formation of TEP in this area.

We have analysed the diversity of the bacteria, which grow after addition of concentrated airborne particles and desert dust in different microcosms combinations with water samples from oligotrophic alpine lakes. We used, on the one hand, airborne bacteria transported by an African dust plume and collected in a high mountain area in the central Pyrenees (Spain). On the other hand, we collected desert dust in Mauritania (c. 3000 km distance, and a few days estimated airborne journey), a known source region for dust storms in West Africa, which originates many of the dust plumes landing on Europe. In all the dust-amended treatments we consistently observed bacterial growth of common phyla usually found in freshwater ecosystems, i.e. Alpha-, Beta- and Gammaproteobacteria, Actinobacteria, and a few Bacteroidetes, but with different composition based on lake water pretreatment and dust type. Overall, we tentatively split the bacterial community in (i) typical freshwater non-airborne bacteria, (ii) cosmopolitan long-distance airborne bacteria, (iii) non-freshwater low-distance airborne bacteria, (iv) non-freshwater long-distance airborne soil bacteria and (v) freshwater non-soil airborne bacteria. We identified viable long-distance airborne bacteria as immigrants in alpine lakes (e.g. Sphingomonas-like) but also viable putative airborne pathogens with the potential to grow in remote alpine areas (Acinetobacter-like and Arthrobacter-like). Generation of atmospheric aerosols and remote dust deposition is a global process, largely enhanced by perturbations linked to the global change, and high mountain lakes are very convenient worldwide model systems for monitoring global-scale bacterial dispersion and pathogens entries in remote pristine environments.

Sunlight reacts with dissolved organic matter (DOM) modifying its availability as bacterial substrate. We assessed the impact of DOM photoproducts and mineral nutrient supply on bacterial growth in seven inland waters from the South of Spain, where DOM is characterized by low chromophoric content and long residence time. Factorial experiments were performed with presence vs absence of DOM photoproducts and mineral nutrient supply. In six of the seven experiments, we found a significant and negative effect of DOM photoproducts on bacterial growth and a significant and positive effect of mineral nutrient supply. The interaction of these two factors leaded to a compensation of negative effects of photoproducts by availability of mineral nutrients. Dissolved organic matter diagenetic status and the ionic environment where organic carbon is dissolved can be influencing bacterial DOM processing.

Abstract: Traditional aquaculture produces wastewater with high nutrient and organic matter concentrations. Poly‐culture can improve this problem including “extractive species” such as sea cucumbers along with the primary species. The influence of sea cucumbers on transparent exopolymer particles (TEP) (i.e. biofilm precursors) has not been previously explored. Here, we monitored during 1 year the concentration of nutrients, total organic carbon (TOC), particulate organic matter (POM), TEP, chlorophyll‐a and bacteria in two tanks of 50,000 L. One tank only contained Anemonia sulcata, whereas the other tank also included holothurians. To complement these time‐series, we performed three short‐term experiments in smaller (300 L) tanks. Three tanks contained A. sulcata plus Holothuria tubulosa (+H treatment) and other four tanks contained only A. sulcata (−H treatment). In the time‐series, we found that the concentration of ammonium, nitrate, TOC, POM, TEP and bacteria in the effluent of the tank with holothurians was lower than in the effluent of the tank without holothurians. The three experiments confirmed that the holothurians reduced significantly nitrates, bacterial abundance and TEP concentration. Therefore, these invertebrates can control bacterial proliferation and prevent biofilm formation minimizing likely the risk of outbreak of pathogenic bacteria and improving the hygiene of the tanks. [ABSTRACT FROM AUTHOR]

Marine invertebrates, as holobionts, contain symbiotic bacteria that coevolve and develop antimicrobial substances. These symbiotic bacteria are an underexplored source of new bioactive molecules to face the emerging antibiotic resistance in pathogens. Here, we explored the antimicrobial activity of bacteria retrieved from the microbiota of two sea anemones (Anemonia sulcata, Actinia equina) and two holothurians (Holothuria tubulosa, Holothuria forskali). We tested the antimicrobial activity of the isolated bacteria against pathogens with interest for human health, agriculture and aquaculture. We isolated 27 strains with antibacterial activity and 12 of these isolates also showed antifungal activity. We taxonomically identified these strains being Bacillus and Vibrio species the most representative producers of antimicrobial substances. Microbiome species composition of the two sea anemones was similar between them but differed substantially of seawater bacteria. In contrast, microbiome species composition of the two holothurian species was different between them and in comparison with the bacteria in holothurian feces and seawater. In all the holobiont microbiomes Bacteroidetes was the predominant phylum. For each microbiome, we determined diversity and the rank-abundance dominance using five fitted models (null, pre-emption, log-Normal, Zipf and Zipf-Mandelbrot). The models with less evenness (i.e. Zipf and Zipf-Mandelblot) showed the best fits in all the microbiomes. Finally, we tracked (using the V4 hypervariable region of 16S rRNA gene) the relative abundance of these 27 isolates with antibacterial activity in the total pool of sequences obtained for the microbiome of each holobiont. Coincidences, although with extremely low frequencies, were detected only in the microbiome of H. forskali. This fact suggests that these isolated bacteria belong to the long tail of rare symbiotic bacteria. Therefore, more and more sophisticated culture techniques are necessary to explore this apparently vast pool of rare symbiontic bacteria and to determine their biotechnological potentiality. [ABSTRACT FROM AUTHOR]

Furthermore, panels c and d in the figure 1 were inverted and consequently, the figure did not match with the text and the figure caption. B Correction to: Microbial Ecology b https://doi.org/10.1007/s00248-022-02109-2 Due to a typesetting mistake during coding in R, units in the x-axis of figure 1c and d were wrongly written with a negative exponent (i.e. 10 SP -1 sp , 10 SP -2 sp , 10 SP -3 sp ,10 SP -4 sp ), while the exponent should be positive (i.e. 10 SP 1 sp , 10 SP 2 sp , 10 SP 3 sp ,10 SP 4 sp ). [Extracted from the article]

Abstract The long-range transport of bioaerosols takes place in the free troposphere and has lately gained a renewed interest in both environmental and health-related disciplines. Sampling free troposphere bioaerosols has been, however, historically challenging and requires of expensive and complex facilities. We analysed different bacterial bioaerosols studies carried out by sequencing of the 16S rRNA gene, available from the literature. The dataset was compared with bacterial bioaerosols present in rain and dry deposition passively collected at high-elevation sites in Sierra Nevada along a set of sampling periods lasting 3 years. Up to 65% of OTUs and 82% of the bacterial genera were shared between wet and dry bioaerosols. Interestingly, only Oxalobacteraceae were notably more abundant in wet deposition, with Noviherbaspirillum and Massilia as dominant genera. We demonstrated that the bacterial composition of bioaerosols collected by passive natural deposition at high-elevated mountains were closer to the bacterial microbiome from the free troposphere. Interestingly, the meta-analysis showed a different bacterial composition and community structure in bacterial bioaerosols collected at low-elevated areas, over the open ocean, or during desert dust events. Since the boundary layer can be easily reached in high mountain areas, and the local landscape is surrounded by rocks and meadows, alpine stations are potentially optimal research sites with reduced influence of surface aerosols, minimizing local contaminations. Consequently, sampling alpine bioaerosols could be a good proxy for bioaerosols monitoring, long-range dispersal studies, and the dynamic characterization of the free troposphere microbiome. Highlights • Different bacterial bioaerosols exist at high-elevation mountains, low lands, over the open ocean, or during desert dust events. • Bacterial bioaerosols ground-sampled above the boundary layer were largely convergent with the free troposphere microbiome. • Airborne sampling stations at high-elevation mountains are a good proxy for long-term monitoring of the globally transported microbiome. [ABSTRACT FROM AUTHOR]