Two different hypotheses have been raised as to how temperature affects resource allocation in microorganisms. The translation‐compensation hypothesis (TCH) predicts that the increase in enzymatic ...efficiency with temperature results in fewer required ribosomes per cell and lower RNA:protein ratio. In contrast, the growth rate hypothesis (GRH) predicts that increasing the growth rate with temperature requires more ribosomes and hence a higher cellular RNA:protein. We tested these two hypotheses in laboratory cultures of Prochlorococcus and Alteromonas as well as over an annual cycle in the Eastern Mediterranean Sea. The RNA:protein of Alteromonas mostly decreased with temperature in accordance with the TCH, while that of Prochlorococcus increased with temperature, as predicted by the GRH. No support was found for either hypothesis in surface waters from the Eastern Mediterranean, whereas the fraction of phosphorus in RNA was positively correlated with per‐cell bacterial production in the deep chlorophyll maximum, supporting the GRH in this niche. A considerable part of the cellular phosphorus was not allocated to RNA, DNA, phospholipids or polyphosphate, raising the question which cellular molecules contain these P reserves. While macromolecular quotas differed significantly between laboratory cultures and field samples, these were connected through a power law, suggesting common rules of resource allocation.
N
fixation by planktonic heterotrophic diazotrophs is more wide spread than previously thought, including environments considered "unfavorable" for diazotrophy. These environments include a ...substantial fraction of the aquatic biosphere such as eutrophic estuaries with high ambient nitrogen concentrations and oxidized aphotic water. Different studies suggested that heterotrophic diazotrophs associated with aggregates may promote N
fixation in such environments. However, this association was never validated directly and relies mainly on indirect relationships and different statistical approaches. Here, we identified, for the first time, a direct link between active heterotrophic diazotrophs and aggregates that comprise polysaccharides. Our new staining method combines fluorescent tagging of active diazotrophs by nitrogenase-immunolabeling, polysaccharides staining by Alcian blue or concanavalin-A, and total bacteria via nucleic-acid staining. Concomitant to N
fixation rates and bacterial activity, this new method provided specific localization of heterotrophic diazotrophs on artificial and natural aggregates. We postulate that the insights gained by this new visualization approach will have a broad significance for future research on the aquatic nitrogen cycle, including environments in which diazotrophy has traditionally been overlooked.
Large amounts of dust and atmospheric aerosols, originating from surrounding desert areas (e.g., Sahara and Middle East) are deposited annually on the surface of the Eastern Mediterranean Sea. These ...depositions can provide high amounts of micro (such as Fe, Zn, Co) and macro nutrients (such as P and N) to supplement nutrient-poor surface waters- that typically limit primary productivity and also dinitrogen (N2) fixation in many marine environments. Here, we studied the impact of the atmospheric deposition of dust and aerosols on N2 fixation in the Cretan Sea (Eastern Mediterranean Sea). Mixed polluted aerosols (hereafter A) and Saharan dust (hereafter SD) were added to nine mesocosms (3-m3 each) containing surface mixed layer seawater (~10 m), and N2 fixation was evaluated for 6 days during May 2012 (springtime). The addition of SD triggered a rapid (30 h) and robust (2-4 fold) increase in N2 fixation rates that remained high for 6 days and contributed 3-8% of the primary productivity. The A addition also resulted in higher N2 fixation rates compared to the unamended control mesocosms, although the responses were less profound (1.5-2 fold) and accounted for only 2-4% of the primary productivity. The microbial community responded differently to the two additions. Heterotrophic bacterial N2 fixers dominated the diazotroph community in A and the control mesocosms, while the non-filamentous cyanobacterial group Trichodesmium prevailed in the SD treatment (68% of all the operational taxonomic units, verified by qPCR analyses). Our results indicate that the aerosol source, its route prior to deposition, and its specific chemical composition, can alter the diazotrophic diversity and activity in the Eastern Mediterranean Sea and may thus impact both the N and C dynamics in this impoverished environment.
Criteria for eutrophication related parameters to achieve and preserve good environmental status (GES) of the oligotrophic Israeli Mediterranean coast were proposed for nutrients, chlorophyll-a ...(Chl-a) and suspended particulate matter (SPM) concentrations. The criteria were derived from current conditions, the best choice for the area that has undergone large and irreversible ecological changes compared to the pristine background. A five-year data set (2010–2014, ca. 800 data points) was analyzed using statistical methods and best professional judgement. The coastal waters were divided into four provinces, data gaps were identified, and seasonal reference and threshold values for each province determined as the median and 1.5 times the median, respectively. Application of the derived criteria to data up to 2016 showed the coastal waters to be mainly in GES, with a few exceptions. Simplification of the proposed criteria for environmental management was addressed as well.
•Environmental assessment criteria for eutrophication in the oligotrophic Israeli Mediterranean coast are presented.•Reference and threshold values were derived from current conditions (2010–2014).•Coastal water provinces were assessed for their present environmental status.•Simplification of the criteria, for environmental management, is proposed.
The effects of atmospheric deposition on plankton community structure were examined during a mesocosm experiment using water from the Cretan Sea (Eastern Mediterranean), an area with a high frequency ...of atmospheric aerosol deposition events. The experiment was carried out under spring-summer conditions (May 2012). The main objective was to study the changes induced from a single deposition event, on the autotrophic and heterotrophic surface microbial populations, from viruses to zooplankton. To this end, the effects of Saharan dust addition were compared to the effects of mixed aerosol deposition on the plankton community over 9 days. The effects of the dust addition seemed to propagate throughout the food-web, with changes observed in nearly all of the measured parameters up to copepods. The dust input stimulated increased productivity, both bacterial and primary. Picoplankton, both autotrophic and heterotrophic capitalized on the changes in nutrient availability and microzooplankton abundance also increased due to increased availability of prey. Five days after the simulated deposition, copepods also responded, with an increase in egg production. The results suggest that nutrients were transported up the food web through autotrophs that were favored by the Nitrogen supplied through both treatments. Although the effects of individual events are generally short lived, increased deposition frequency and magnitude of events is expected in the area, due to predicted reduction in rainfall and increase in temperature, which can lead to more persistent changes in plankton community structure. Here we demonstrate how a single dust deposition event leads to enhancement of phytoplankton and microzooplankton and can eventually, through copepods, transport more nutrients up the food web in the Eastern Mediterranean Sea.
Seawater reverse osmosis (SWRO) is becoming an increasingly important source of potable water in arid and semi-arid regions worldwide. Discharge of brine-effluent from desalination facilities has ...been shown to significantly impact coastal marine ecosystems ranging from seagrass meadows to microbial communities. In this study, we examined the impacts of increased salinity (10% above ambient) and presence of antiscalants (0.2 mg L−1, polyphosphonate-based) on three reef-building coral species; Stylophora pistillata, Acropora tenuis and Pocillopora verrucosa, from the Gulf of Aqaba (northern Red-Sea). Our results indicate that the corals, as well as associated bacteria and algae, were significantly impaired by the elevated salinity and antiscalants, leading to partial bleaching. Specifically, the abundance of bacteria and symbiotic algae as well as calcification rates were typically lower (20–85%, 50–90% and 40–50%, respectively) following incubations with both amendments. However, the impact of desalination brine was often species-specific. Thus, we propose that the ecotoxicological criteria used for hard corals should be determined based on the sensitivity of key species in the community dominating the area affected by desalination discharge.
•Salinity 10% above ambient and polyphosphonate antiscalants have clear impacts on coral's physiology.•Salinity 10% above ambient and polyphosphonate antiscalants significantly reduced bacteria and Symbiodinium abundances.•Calcification rates decreased following the addition of salt and polyphosphonate antiscalants.•Variable responses to increased salinity among coral species suggests species-specific sensitivity.
Desalination outflows frequently discharge brine containing coagulants and antiscalants (e.g. Iron-hydroxides and polyphosphonates) to the coastal environment. Here we examined changes in composition ...and productivity of natural microbial coastal communities in experimental mesocosms treated with either iron-hydroxide (Fe), polyphosphonate (Pn), or a combination of high salinities with both chemicals (All). Within 2 h of addition Fe already altered the microbial community composition, enhanced the bacterial production (BP) and cell specific production (BP/BA), and decreased primary production. Addition of Pn, relieved phosphorus stress as demonstrated by the immediate (within 2 h) and significant reduction in the ecto-enzyme alkaline phosphatase activity (APA). Synergistic effects were observed in the All treatment, reflected by increased production of both primary and bacterial producers as P-stress was relieved. After 10 days of incubation, the microbial community composition changed significantly only in the All treatment. The Fe-only treatment caused a significant decline in autotrophic biomass and in the assimilation number (AN), while in both the Pn and the All treatments the BP/BA increased with the added P. We also examined the microbial community responses in a natural impacted environment at the Ashkelon seawater desalination plant brine discharge site during summer and winter. The community composition differed in elevated-salinity compared with non-impacted stations with higher AN and bacterial efficiencies (BP/BA) measured in summer in the elevated-salinity stations. The seasonal differences in responses may reflect both biotic (i.e. initial community composition) and abiotic factors (currents and residence time of salinity gradients). Our results emphasize that desalination brine discharges that include chemicals such as iron-hydroxide and polyphosphonates can induce physiological and compositional changes in the microbial community. With the expansion of desalination facilities worldwide such shifts in composition and function of the microbial communities may destabilize and change local aquatic food webs and should thus be monitored.
•SWRO brine, Fe-hydroxide, & phosphonate impact microbial physiology & composition.•Fe-hydroxides immediately reduced microbial production & biomass.•Brine, phosphonates, & Fe-hydroxides altered production and composition after 10 d.•At SWRO facility, high salinity sites impacted microbial composition during summer & winter.
Acid processes in the atmosphere, particularly those caused by anthropogenic acid gases, increase the amount of bioavailable P in dust and hence are predicted to increase microbial biomass and ...primary productivity when supplied to oceanic surface waters. This is likely to be particularly important in the Eastern Mediterranean Sea (EMS), which is P limited during the winter bloom and N&P co-limited for phytoplankton in summer. However, it is not clear how the acid processes acting on Saharan dust will affect the microbial biomass and primary productivity in the EMS. Here, we carried out bioassay manipulations on EMS surface water on which Saharan dust was added as dust (Z), acid treated dust (ZA), dust plus excess N (ZN), and acid treated dust with excess N (ZNA) during springtime (May 2012) and measured bacterioplankton biomass, metabolic, and other relevant chemical and biological parameters. We show that acid treatment of Saharan dust increased the amount of bioavailable P supplied by a factor of ~40 compared to non-acidified dust (18.4 vs. 0.45 nmoles P mg super(-1) dust, respectively). The increase in chlorophyll, primary, and bacterial productivity for treatments Z and ZA were controlled by the amount of N added with the dust while those for treatments ZN and ZNA (in which excessive N was added) were controlled by the amount of P added. These results confirm that the surface waters were N&P co-limited for phytoplankton during springtime. However, total chlorophyll and primary productivity in the acid treated dust additions (ZA and ZNA) were less than predicted from that calculated from the amount of the potentially limiting nutrient added. This biological inhibition was interpreted as being due to labile trace metals being added with the acidified dust. A probable cause for this biological inhibition was the addition of dissolved Al, which forms potentially toxic Al nanoparticles when added to seawater. Thus, the effect of anthropogenic acid processes in the atmosphere, while increasing the flux of bioavailable P from dust to the surface ocean, may also add toxic trace metals such as Al, which moderate the fertilizing effect of the added nutrients.
•Sewage outburst led to a significant eutrophication of coastal water.•Coastal eutrophication enhanced microbial growth.•TEP are released during the later stages of microbial demise.•TEP are only ...partially removed by the pretreatment system.•TMP of the RO membrane increase by 10% seven days after sewage outburst.
Sewage outbursts affect coastal environments as seawater is enriched with nutrients, organic matter and microbes, thus can potentially impair seawater reverse osmosis (SWRO) desalination. In this study, we evaluated how municipal sewage outbursts affect SWRO desalination in a pilot-scale system. To this end, feedwater characteristics (i.e., coastal water), the removal efficiency of organic foulants by a dual-media gravity filter, and cartridge micro-filtration were determined daily for 12 days. Permeate water flux was maintained constant during the study, while trans-membrane pressure (TMP) was automatically adjusted and continuously monitored. The results indicate that sewage outbursts caused an immediate (∼1 d) buildup of phyto/bacterioplankton biomass (up to 10-fold), and enhanced activity (maximal 30-fold) followed by an increase in transparent exopolymer particle (TEP) concentrations. After sewage addition, algal biomass was significantly removed by the pretreatment system (72–90%), while a considerable fraction of the bacterial biomass (42–65%) and TEP (53–65%) passed these procedures. The result was a negative impact on the desalination performance reflected by a significant increase (> 10%) in RO-TMP 7.5 d after the sewage addition. Our results indicate on a direct link between sewage outbursts, pretreatment efficiency, and SWRO desalination. Nevertheless, these findings can lead to new avenues for the development of science-based operational protocols to minimize the deleterious effects of abrupt sewage outbursts on SWRO desalination.
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Phytoplankton-bacterium interactions are mediated, in part, by phytoplankton-released dissolved organic matter (DOMp). Two factors that shape the bacterial community accompanying phytoplankton are ...(i) the phytoplankton producer species, defining the initial composition of released DOMp, and (ii) the DOMp transformation over time. We added phytoplankton DOMp from the diatom Skeletonema marinoi and the cyanobacterium Prochlorococcus marinus MIT9312 to natural bacterial communities from the eastern Mediterranean and determined the bacterial responses over a time course of 72 h in terms of cell numbers, bacterial production, alkaline phosphatase activity, and changes in active bacterial community composition based on rRNA amplicon sequencing. Both DOMp types were demonstrated to serve the bacterial community as carbon and, potentially, phosphorus sources. Bacterial communities in diatom-derived DOM treatments maintained higher Shannon diversities throughout the experiment and yielded higher bacterial production and lower alkaline phosphatase activity compared to cyanobacterium-derived DOM after 24 h of incubation (but not after 48 and 72 h), indicating greater bacterial usability of diatom-derived DOM. Bacterial communities significantly differed between DOMp types as well as between different incubation times, pointing to a certain bacterial specificity for the DOMp producer as well as a successive utilization of phytoplankton DOM by different bacterial taxa over time. The highest differences in bacterial community composition with DOMp types occurred shortly after DOMp additions, suggesting a high specificity toward highly bioavailable DOMp compounds. We conclude that phytoplankton-associated bacterial communities are strongly shaped by the phytoplankton producer as well as the transformation of its released DOMp over time.
Phytoplankton-bacterium interactions influence biogeochemical cycles of global importance. Phytoplankton photosynthetically fix carbon dioxide and subsequently release the synthesized compounds as dissolved organic matter (DOMp), which becomes processed and recycled by heterotrophic bacteria. Yet the importance of phytoplankton producers in combination with the time-dependent transformation of DOMp compounds on the accompanying bacterial community has not been explored in detail. The diatom
and the cyanobacterium Prochlorococcus marinus MIT9312 belong to globally important phytoplankton genera, and our study revealed that DOMp of both species was selectively incorporated by the bacterial community. The producer species had the highest impact shortly after DOMp appropriation, and its effect diminished over time. Our results improve the understanding of the dynamics of organic matter produced by phytoplankton in the oceans as it is utilized and modified by cooccurring bacteria.
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