Dominant oceanic bacteria secure phosphate using a large extracellular buffer

The ubiquitous SAR11 and Prochlorococcus bacteria manage to maintain a sufficient supply of phosphate in phosphate-poor surface waters of the North Atlantic subtropical gyre. Furthermore, it seems that their phosphate uptake may counter-intuitively be lower in more productive tropical waters, as if their cellular demand for phosphate decreases there. By flow sorting 33P-phosphate-pulsed 32P-phosphate-chased cells, we demonstrate that both Prochlorococcus and SAR11 cells exploit an extracellular buffer of labile phosphate up to 5–40 times larger than the amount of phosphate required to replicate their chromosomes. Mathematical modelling is shown to support this conclusion. The fuller the buffer the slower the cellular uptake of phosphate, to the point that in phosphate-replete tropical waters, cells can saturate their buffer and their phosphate uptake becomes marginal. Hence, buffer stocking is a generic, growth-securing adaptation for SAR11 and Prochlorococcus bacteria, which lack internal reserves to reduce their dependency on bioavailable ambient phosphate

Riječ akademika Josipa Torbarine, tajnika Razreda za filologiju JAZU

Physical ocean processes (ice-melt, island run-off and upwelling of nutrients) were hypothesised to affect the bacterioplankton composition in the surface mixed layer of the Scotia Sea during the austral summer of 2003, and this was investigated using flow cytometry and catalysed reporter deposition fluorescence in situ hybridisation (CARD-FISH) techniques. The bacterioplankton was composed predominantly of Alphaproteobacteria (PB), comprising SAR11, Roseobacterspp. and SAR116 groups, followed by Sphingobacteria/Flavobacteria and Gammaproteobacteria, including SAR86. Two distinct bacterioplankton communities were identified, largely based on bacterioplankton abundance, which varied from 0.3 ± 0.06 × 106 cells ml–1 in the west to 0.8 ± 0.3 × 106 cells ml–1 in the east, and a corresponding difference in SAR11 percentages of 30 ± 15% in the west compared to 5 ± 5% in the east. The western community was present in waters that were largely in an over-wintered, pre-bloom condition. The eastern bacterioplankton community was associated with phytoplankton blooms developed within the eastern Scotia Sea nutrient upwelling zone, where the Antarctic Circumpolar Current (ACC) encounters the shallow bathymetry associated with the Scotia Arc, in combination with seasonal ice-melt and island effects that enabled surface water stratification

Phytoplankton responses and associated carbon cycling during shipboard carbonate chemistry manipulation experiments conducted around Northwest European shelf seas

The ongoing oceanic uptake of anthropogenic carbon dioxide (CO2) is significantly altering the carbonate chemistry of seawater, a phenomenon referred to as ocean acidification. Experimental manipulations have been increasingly used to gauge how continued ocean acidification will potentially impact marine ecosystems and their associated biogeochemical cycles in the future; however, results amongst studies, particularly when performed on natural communities, are highly variable, which in part likely reflects inconsistencies in experimental approach. To investigate the potential for identification of more generic responses and greater experimentally reproducibility, we devised and implemented a series of highly replicated (n = 8), short term (2–4 days) multi-level (≥ 4 conditions) carbonate chemistry/nutrient manipulation experiments on a range of natural microbial communities sampled in Northwest European shelf seas. Carbonate chemistry manipulations and resulting biological responses were found to be highly reproducible within individual experiments and to a lesser extent between geographically different experiments. Statistically robust reproducible physiological responses of phytoplankton to increasing pCO2, characterized by a suppression of net growth for small sized cells (< 10 µm), were observed in the majority of the experiments, irrespective of nutrient status. Remaining between-experiment variability was potentially linked to initial community structure and/or other site-specific environmental factors. Analysis of carbon cycling within the experiments revealed the expected increased sensitivity of carbonate chemistry to biological processes at higher pCO2 and hence lower buffer capacity. The results thus emphasize how biological-chemical feedbacks may be altered in the future ocean

Amino acid uptake of Prochlorococcus spp. in surface waters across the South Atlantic Subtropical Front

To test the hypothesis that surface-living Prochlorococcus spp. (Pro) cyanobacteria metabolism declines towards the boundaries of its natural habitat, a latitudinal transect of surface waters was sampled from the centre of the Southern Atlantic Gyre (SAG, 20 to 35° S) to the South Subtropical Frontal Zone (SSFZ, 35 to 45° S). Along this transect, amino acid uptake rates of Pro, Synechococcus spp. (Syn) and an average bacterioplankton cell were determined using 35S-methionine precursor and flow-cytometry sorting, with methionine uptake rate as an index of cellular metabolic activity. Methionine and possibly other amino acids were a very minor nutrient source for Syn, while their contribution to Pro production was significant. Contrary to expectations, the mean methionine uptake rate per Pro cell in the SSFZ was about 3 times higher than in the SAG. The uptake rates per unit Pro biomass were equal to or higher than that of an average bacterioplankton cell in both the SAG and SSFZ. About 20 and 5% of total bacterioplankton consumption of amino acids could be assigned to Pro in the SAG and SSFZ, respectively. Methionine and leucine turnover rates were 3.5 and 3 times higher in the SSFZ than in the SAG, respectively. These results suggest that Pro remained highly metabolically active and acquired more methionine at its habitat boundaries, despite higher rates of bacterioplankton activity and therefore greater competition, as well as exposure to deep water mixing, low light and low temperature conditions

Bacterioplankton of low and high DNA content in the suboxic waters of the Arabian Sea and the Gulf of Oman: abundance and amino acid uptake

Amino acid uptakes by bacterioplankton of low DNA (LNA) and high DNA (HNA) content, populating the oxygen minimum zone (OMZ: <5 µM O2) and adjacent oxygen-depleted waters (5 to 50 µM O2), were determined using a 35S-methionine precursor and flow cytometric sorting. The HNA cells were further differentiated into low light scatter (HNA-ls) and high cell light scatter (HNA-hs) groups. Total bacterioplankton methionine uptake strongly correlated (r > 0.998, p < 0.0001) with leucine incorporation into protein and with microbial glucose uptake, suggesting that bacterioplankton growth was controlled by dissolved organic matter, and that methionine uptake could be used as a general estimate for the metabolic activity of bacterioplankton. The variation in methionine uptake depended on the prokaryote group rather than on ambient oxygen concentration, e.g. the numerically dominant LNA cells took 3 to 5 times less precursor than the HNA cells. A percentage of the LNA cells with double the amount of DNA was proposed as an incubation-independent index of growth of the cells in the G2 stage of the cell cycle. The vertical profiles of the percentage of LNA cells in G2 showed pronounced peaks at 300 to 600 m in the OMZ that did not correlate with peaks of either total bacterioplankton abundance or productivity. The present paper underlines the importance of bacterioplankton group studies in the OMZ since high microbial cell abundance does not necessarily mean high metabolic activity and other mechanisms, such as resilience to mortality pressure, have to be investigated

Computable Linear Orders and Limitwise Monotonic Functions

In this paper, we describe the technique of extremely monotonic functions in the theory of computable linear orders. The basic definitions of extremely monotonic functions and their generalizations are given, and a number of their basic properties and applications are presented

Spectral Universality of Linear Orders with One Binary Relation

© 2020, Pleiades Publishing, Ltd. We show the spectral universality of the class of structures that are linear orders with an additional binary relation and hence with an n-ary relation for each n ≥ 2. To this end, we study the category of the structures. We then obtain some other algorithmic properties of the category by using the notion of a computable functor which was studied in recent papers by other authors

Syringe pumped high speed flow cytometry of oceanic phytoplankton

Nanophytoplankton (2–20 µm) are less numerous than picophytoplankton (<2 µm) in the oceans but their biomass and production are comparable and sometimes higher. The accuracy of cytometry-based enumeration of phytoplankton ultimately depends on cell abundance and sample flow rate. Commercial flow cytometers in which sheath and core streams are driven by air pressure cannot produce sufficiently high, stable sample flow rate. The present study demonstrates the applicability of a syringe pump for flow cytometric enumeration of oceanic nanophytoplankton on two meridional transects across the Atlantic Ocean.Methods: Commercially available syringe pumps were used to deliver live phytoplankton samples into a flow cell of standard flow cytometers (FACSort, FACSCalibur, BD) with increased flow rate of > 1.0 ml min-1 compared to the normal air pressure sample delivery of < 0.1 ml min-1. An auxiliary application of syringe pump flow cytometry for calibrating 0.5 µm bead concentration standards is also discussed.Results: The results demonstrated that flow cytometry of samples injected at rates above 0.1 ml min-1 is achievable and worthwhile. Counts of phytoplankton in air and syringe pumped samples agreed closely. Syringe pumping of samples offered a broader range of flow rates up to 0.8–1.0 ml min-1 without detrimental effect on flow cytometric enumeration of cells. The increased number of coincidences at high flow rates led to an approximate 10% decrease of Cyanobacteria counts when the acquisition rate approached 1,000 particles s-1, but seemed to have a lesser effect on counting rarer phytoplankton. The syringe pump flow cytometry allowed enumeration of phytoplankton groups at concentrations of 5–100 cells ml-1, cell concentrations equivalent to those of Cyanobacteria in the twilight deep ocean.Conclusion: The proposed syringe pump modification of a FACS instrument represents a significant improvement for accurate enumeration of the less abundant phytoplankton and so gives better estimations of phytoplankton distribution and standing stocks

Effect of appendicularians and copepods on bacterioplankton composition and growth in the English Channel

We compared the effects of the presence of the appendicularian Oikopleura dioica and the copepods Acartia clausii and Calanus helgolandicus on the coastal bacterioplankton community off Plymouth. Mesozooplankton were added to water samples and bacterioplankton growth was monitored by flow cytometry. Phylogenetic composition of bacterioplankton was analysed using fluorescence in situ hybridisation (FISH) with rRNA-targeted oligonucleotide probes. The bacterioplankton composition did not change in the presence of either appendicularians or copepods, and generally the same proportions of bacterioplankton groups were determined. In late spring, 15 ± 2% of cells hybridised with a probe specific to the Kingdom Archaea. The majority of cells (88 ± 2%) belonged to the Kingdom Bacteria, and 86% of cells were identified using group-specific probes. The Cytophage-Flavobacterium cluster dominated the community, comprising 64 ± 0.5% of cells. The g-proteobacteria were the second abundant group, comprising 11 ± 0.5% of cells, and the SAR86 cluster of g-proteobacteria accounted for 6 ± 5%. The a-proteobacteria comprised 10 ± 5% of bacterioplankton, and the Roseobacteria related cluster represented 9 ± 3% of cells. The reduction of bacterioplankton growth caused by appendicularian bacterivory was 0.4 to 14% ind.-1 l-1, and the total appendicularian population could reduce bacterial growth in coastal waters in late spring-summer by up to 9%. In contrast to the appendicularians the copepods stimulated bacterial growth, and in summer the bacterioplankton growth may be increased by up to 13% by the combined effect of dominant copepod populations. Thus, the appendicularians and copepods had an opposite but moderate effect on the bacterioplankton growth and no effect on the bacterioplankton composition

Flow cytometric enumeration of DNA-stained oceanic planktonic protists

The aim of this study was to test the practicality of enumerating fixed, DNA-stained heterotrophic protists (H) and phototrophic protists (P) in contrasting regions of the Atlantic Ocean. Oceanic protists were enumerated using a standard flow cytometer (FACSort, BD) at an enhanced flow rate of up to 1.0 mL min–1 to increase numbers of counted cells. The enumeration error of protists decreased hyperbolically from 30–40 to < 5% corresponding to the number (<100 to > 2000) of enumerated cells. H and P were discriminated using the extra red chlorophyll-derived plastidic fluorescence of the latter. The relationship between counts of stained and unstained fixed and unfixed P was statistically close to 1:1, confirming the accuracy of stained protist counting by flow cytometry and adequate discrimination of P from H cells. The estimated average abundance of H in the surface mixed layer of the southern and northern oligotrophic gyres was remarkably similar, with 400 ± 140 and 450 ± 60 cells mL–1, respectively, adding further evidence to the suggestion that these regions are in steady state. In agreement with earlier studies in more productive aquatic environments, a significant correlation (correlation coefficient 0.84, P < 0.0001) was found between the H and the total bacterioplankton numbers, with an average ratio of 1300 prokaryotes to 1 H cell, suggesting a relatively constant trophic interaction between these two groups. This study demonstrates that flow cytometric enumeration of protists is 100 times faster compared with microscopy and, thus, represents a major improvement for quantifying protists in ocean waters, including oligotrophic gyres