Planktonic Populations Research Articles

Direct and Indirect Effects of Resource P-Limitation Differentially Impact Population Growth, Life History and Body Elemental Composition of a Zooplankton Consumer.

One of the central tenets of ecological stoichiometry is that consumer growth rate is strongly determined by food phosphorus (P) content. In planktonic organisms population growth rates of zooplankton have repeatedly been shown to be reduced when fed with P-limited algal food sources. However, P-limitation may also affect other quality-related aspects of algae, such as biochemical composition or palatability. We studied the population growth, detailed life history and body elemental composition of the herbivorous rotifer, Brachionus calyciflorus, in response to three different food quality treatments: algae cultured in high phosphorus conditions (average algal molar C:P ≈ 112, ‘HP’), algae cultured in low P conditions (molar C:P ≈ 631, ‘LP’) and low-P cultured algae spiked with P just before feeding (molar C:P ≈ 113, ‘LP+P’). LP+P algae thus combined high P content with a history of growth under P-limited conditions. Total P content and the C:P ratio of rotifers in the LP+P treatment equaled those of rotifers in the HP treatment. Rotifer population growth rates were higher in HP than in LP and intermediate in the LP+P treatment. Similarly, many life history traits observed for animals in the LP+P treatment, such as somatic growth rate, age at maturity, and egg production rate were also intermediate to those observed in the LP and HP treatments. However, there were important deviations from this pattern: size at first reproduction and egg mortality in the LP+P treatment equaled the HP treatment, whereas size and development time of the first eggs equaled those of the LP treatment. Our results indicate that elemental limitation cannot fully explain reduced performance of consumers fed with P-limited algae and strongly suggest that indirect, non-stoichiometric effects of P-limitation, e.g., via changes in biochemical composition or morphology of the algae also play a major role. Furthermore, our study highlights that such indirect effects have a differential impact on major fitness components and may as such also determine the population dynamics and demographic structure of consumer populations.

Имитационное моделирование роста биомассы фитопланктона в Куйбышевском водохранилище

A one-dimensional numerical model of the temporal variability of vertical distribution of phytoplankton biomass in the dam reach of the Kuibyshev reservoir was developed on the basis of the known representations of the development of populations of plankton. The model is based on physical processes in which the specific growth rate of phytoplankton is limited by the parameters of mineral phosphorus, water temperature, illumination, hydrodynamics, death and algal consumption by zooplankton. As a result of field hydrochemical and hydrobiological observations carried out in spring and summer 2012 original information concerning adaptation and evaluation of the adequacy of the model to the specific conditions of the Kuibyshev reservoir was obtained. The mechanism of quasi-periodic spikes in the phytoplankton biomass as the result of seasonal changes in environmental factors was reveald in the process of analyzing of the field observations and numerical experiments data. The paper presents a model calculation of phytoplankton in the Kuibyshev reservoir in case of twofold reduction of phosphorus discharge in the Volga basin. The calculation of this scenario shows that the expected response of phytoplankton is sensitive enough to lead to reduction of the biomass and improvement of the trophic status of the Volga reservoirs. Verification of the simulation results showed satisfactory correlation with the data of field observations; this enables to use the developed model for diagnostic and prognostic purposes.

Distribution of the invasive calanoid copepod Pseudodiaptomus marinus (Sato, 1913) in the Belgian part of the North Sea

The population structure of the non-indigenous calanoid copepod Pseudodiaptomus marinus (Sato, 1913) in the Belgian part of the North Sea (BPNS) is reported for the first time. Detailed P. marinus abundance data including sex and age class of the individuals was gathered on a monthly basis from February 2015 to February 2016 at six sites within the BPNS and Belgian harbors. Relevant environmental variables were analysed to identify potential drivers explaining the population structure of P. marinus within the BPNS. The abundances found were unexpectedly high, with peak densities of up to 560 +/- 163 ind.m(-3). Even though P. marinus was found in all stations sampled, large spatial and temporal differences were found in the abundance of this species. P. marinus population structure was best explained by water temperature and chlorophyll a concentrations, while salinity and concentrations of dissolved inorganic nitrogen did not influence the distribution. The reported high abundances of the species, especially in the harbor of Zeebrugge, together with the high relative abundances of copepodites indicate that the species is able to reproduce within the BPNS and Belgian harbors, possibly leading to an established, permanent population. It is crucial to study the distribution of this species for a longer period in order to determine the possible establishment of this species in the BPNS and consequences for local planktonic populations.

Modeling of production and destruction processes in coastal systems on a supercomputer

The paper covers the development and research mathematical model of production and destruction processes in coastal system, based on the modern information technologies and computational methods to improve the accuracy of predictive modelling the ecological situations in waters during the summer. The model takes into account following: the movement of water flow; microturbulent diffusion; gravitational settling of pollutants; nonlinear interaction of plankton populations; the impact of salinity, temperature, as well as the pollution entrance and deposition from river flows and air. The scheme with weights was proposed for discretization of the developed model, that allowed significantly reduce the error and the computational time. Practical significance of the work is that the proposed model was software implemented; the limits and prospects of its use were defined. On the basis of a supercomputer, the experimental software was designed for mathematical modelling of possible development scenarios of the ecosystems of coastal waters on the example of the Azov Sea in the summer period, taking into account the influence of environment. Parallel implementation was performed using the decomposition methods for computationally labours diffusion-convection problems taking into account the architecture and parameters of multiprocessor computer system.

Intelligent plankton image classification with deep learning

Planktons are extremely diverse groups of organisms that exist in large water columns. They are sources of food for fishes and many other marine life animals. The plankton distribution is essential for the survival of many ocean lives and plays a critical role in marine ecosystem. In recent years, intelligent image classification systems were developed to study plankton distribution through classification of the plankton images taken by underwater imaging devices. Due to the significant differences in both shapes and sizes of the plankton population, accurate classification poses a daunting challenge. The mixed quality of the collected images adds more difficulty to the task. In this paper, we present an intelligent machine learning system built on convolutional neural networks (CNN) for plankton image classification. Unlike most of the existing image classification algorithms, CNN based systems do not depend on features engineering and they can be efficiently extended to encompass new classes. The experimental results on SIPPER image datasets show that the proposed system achieves higher accuracy compared with the state-of-the-art approaches. The new system is also capable of learning a much larger number of plankton classes.

Sequence stratigraphic interpretation of parts of Anambra Basin, Nigeria using geophysical well logs and biostratigraphic data

The Anambra basin constitutes the southeastern lower portion of the Benue Trough, which is a large structural depression that is divided into lower, middle and upper parts; and is one of the least studied inland sedimentary basins in Nigeria. Sequence stratigraphic interpretation had been carried out in parts of the Anambra Basin using data from three wells (Alo-1 Igbariam-1 and Ajire-1). Geophysical well logs and biostratigraphic data were integrated in order to identify key bounding surfaces, subdivide the sediment packages, correlate sand continuity and interpret the environment of deposition in the fields. Biostratigraphic interpretation, using foraminifera and plankton population and diversity, reveals five maximum flooding surfaces (MFS) in the fields. Five sequence boundaries (SB) were also identified using the well log analysis. Four 3rd order genetic sequences bounded by maximum flooding surfaces (MFS-1 to MFS-6) were identified in the areas; four complete sequences and one incomplete sequence were identified in both Alo-1 and Igbariam-1 wells while Ajire-1 has an no complete sequence. The identified system tracts delineated comprises Lowstand Systems Tracts (progradational to aggradational to retrogradational packages), Transgressive Systems Tracts (retrogradational packages) and Highstand Systems Tracts (aggradational to progradational packages) in each well. The sand continuity across the fields reveal sands S1 to S5 where S1 is present in Ajire-1 well and Igbariam-1 well but not in Alo-1 well. The sands S4 to S5 run across the three fields at different depths. The formations penetrated by the wells starting from the base are; Nkporo Formation (Campanian), Mamu Formation (Late Campanian to Early Maastrichtian), Ajali Sandstone (Maastrichtian), Nsukka Formation (Late Maastrichtian to Early Palaeocene), Imo Formation (Palaeocene) and Nanka Sand (Eocene). The environments of deposition revealed are from coastal to bathyal. The sands of lowstand system tract and highstand system tract found in Ajali, Nsukka, Nkporo and Imo (Ebenebe Sandstone) Formations show good continuity and as such good reservoir qualities while the shales of the transgressive system tracts which includes the Imo Formation, Mamu, and Nkporo Formations where most of the maximum flooding surfaces were delineated, can serve as seals to the numerous reservoir units. Combinations of the reservoir sands of the lowstand system tract and highstand system tract and the shale units of the transgressive system tract can form good stratigraphic traps for hydrocarbon and hence should be hydrocarbon exploration targets.

Dinoflagellate cyst abundance is positively correlated to sediment organic carbon in Sydney Harbour and Botany Bay, NSW, Australia.

There is growing public concern about the global expansion of harmful algal bloom species (HABs), with dinoflagellate microalgae comprising the major portion of the harmful taxa. These motile, unicellular organisms have a lifecycle involving sexual reproduction and resting cyst formation whereby cysts can germinate from sediments and 'seed' planktonic populations. Thus, investigation of dinoflagellate cyst (dinocyst) distribution in sediments can provide significant insights into HAB dynamics and contribute to indices of habitat quality. Species composition and abundance of dinocysts in relation to sediment characteristics were studied at 18 stations in two densely populated temperate Australian estuaries, Sydney Harbour (Parramatta River/Port Jackson; PS) and Botany Bay (including Georges River; GB). Eighteen dinocyst taxa were identified, dominated by Protoceratium reticulatum and Gonyaulax sp.1 in the PS estuary, together with Archaeperidinium minutum and Gonyaulax sp.1 in the GB estuary. Cysts of Alexandrium catenella, which is one of the causative species of paralytic shellfish poisoning (PSP), were also detected in both estuaries. Out of the measured sediment characteristics (TOC, Cd, Cr, Cu, Fe, Pb, Mn, Ni, Zn and polycyclic aromatic hydrocarbons), TOC was the parameter explaining most of the variation in dinocyst assemblages and was positively correlated to most of the heavy metals. Given the significant relationship between sediment TOC and dinocyst abundance and heavy metal concentrations, this study suggests that sediment TOC could be broadly used in risk management for potential development of algal blooms and sediment contamination in these estuaries.

Adjacent environments contribute to the increase of zooplankton species in a neotropical river

Abstract Aim: The distribution of the zooplankton community along the Paraná River and in adjacent environments (tributaries and lakes) was evaluated, as well as the contribution of the community present in these environments to the species composition of the Paraná River. It was expected that the ensemble of species found in the last sampling site of the Paraná River would represent the accumulation of species found in the upstream sites. Methods The community was sampled at 25 sites, during 2013 and 2014, and the species richness and composition were determined. The similarity in the composition of the community between the environments was evaluated using cluster analysis, and the contribution of the species to the Paraná River was evaluated using nestedness analysis, using the NODF index. Results Overall, 193 species were registered (116 rotifers, 48 cladocerans and 29 copepods), with the majority of species considered as rare (163 species). In general, the composition of the community in the river was dissimilar to the adjacent environments, although there was a relationship among communities. Rotifers presented broad distribution throughout the area. As expected, the zooplanktonic species presented a nested distribution, with the last river site representing a set of the species registered in the upstream sites. Conclusion The results show the importance of the tributaries and lakes to the occurrence of species along the river. The distinct hydrological characteristics of the environments, as well as flow velocity, depth and connectivity, were responsible for the development of planktonic populations in the lakes that arrived in the main river through tributaries. With these results, we suggest the importance of the conservation of adjacent environments of the Paraná River for the maintenance of the zooplanktonic species in this system.

Are the small-sized plankton communities of oligotrophic ecosystems resilient to UVR and P pulses?

Evaluating how environmental stressor interactions influence ecosystem structure and functioning is critical to understanding the response of ecosystems to global change. We exposed a species-poor planktonic community to P pulses in the absence and presence of solar ultraviolet radiation (UVR). We used a field-mesocosm study in an oligotrophic mid-altitude lake to test the hypothesis that interaction between these factors affects the community’s diversity and composition, but not its biomass-size spectrum, making this community resilient in terms of its C-transfer function. Our findings show that P pulses and UVR affected the relative abundance of different planktonic populations. The abundance of phytoplankton was enhanced strongly by P pulses and secondarily by UVR. The UVR × P interaction affected only the smallest autotrophic species. Chlorococcal abundance increased, whereas chroococcal cyanobacteria decreased. However, UVR had a much more pronounced effect than P on the composition of microcrustaceans, and both factors interactively affected their biomass. Hence, the biomass-size spectrum was not resilient to the UVR × P pulse interaction. The steepness of the slope increased under P-pulse conditions because zooplankton were not able to grow concomitantly with phytoplankton, as confirmed by the low zooplankton to phytoplankton biomass ratio (Z∶P). The observed planktonic changes under new foreseeable conditions that include an increase in UVR fluxes and P inputs might decouple the C cycle in inland oligotrophic lakes in the Mediterranean region.

In Vitro Activity of Bacteriophages Against Planktonic and Biofilm Populations Assessed by Flow Cytometry.

The in vitro activity of bacteriophages against planktonic cultures and biofilms is commonly evaluated by culture methods. However, these methods can lead to an underestimation of total bacterial cells when they undergo different physiological states.This chapter describes the methodology used to assess the in vitro activity of bacteriophages against planktonic cultures of bacteria in different metabolic states and biofilm populations by flow cytometry.

Influence of biofilm-forming lactic acid bacteria against methicillin-resistant Staphylococcus aureus (MRSA S547)

ObjectiveTo investigate the antibacterial effect of selected lactic acid bacteria (LAB) biofilms on the planktonic and biofilm population of methicillin-resistant Staphylococcus aureus (MRSA) (S547). MethodsIn this study, biofilm-forming LAB were isolated from tairu and kefir. Isolate Y1 and isolate KF were selected based on their prominent inhibition against test pathogens (using spot-on-agar method and agar-well-diffusion assay) and efficient biofilm production (using tissue culture plate method). They were then identified as Lactobacillus casei (L. casei) Y1 and Lactobacillus plantarum (L. plantarum) KF, respectively using 16S rDNA gene sequencing. The influence of incubation time, temperature and aeration on the biofilm production of L. casei Y1 and L. plantarum KF was also investigated using tissue culture plate method. The inhibitory activity of both the selected LAB biofilms was evaluated against MRSA (Institute for Medical Research code: S547) using L. plantarum ATCC 8014 as the reference strain. ResultsL. casei Y1 showed the highest reduction of MRSA biofilms, by 3.53 log at 48 h while L. plantarum KF records the highest reduction of 2.64 log at 36 h. In inhibiting planktonic population of MRSA (S547), both L. casei Y1 and L. plantarum KF biofilms recorded their maximum reduction of 4.13 log and 3.41 log at 24 h, respectively. Despite their inhibitory effects being time-dependent, both LAB biofilms exhibited good potential in controlling the biofilm and planktonic population of MRSA (S547). ConclusionsThe results from this study could highlight the importance of analysing biofilms of LAB to enhance their antibacterial efficacy. Preferably, these protective biofilms of LAB could also be a better alternative to control the formation of biofilms by pathogens such as MRSA.

Excess labile carbon promotes the expression of virulence factors in coral reef bacterioplankton

Coastal pollution and algal cover are increasing on many coral reefs, resulting in higher dissolved organic carbon (DOC) concentrations. High DOC concentrations strongly affect microbial activity in reef waters and select for copiotrophic, often potentially virulent microbial populations. High DOC concentrations on coral reefs are also hypothesized to be a determinant for switching microbial lifestyles from commensal to pathogenic, thereby contributing to coral reef degradation, but evidence is missing. In this study, we conducted ex situ incubations to assess gene expression of planktonic microbial populations under elevated concentrations of naturally abundant monosaccharides (glucose, galactose, mannose, and xylose) in algal exudates and sewage inflows. We assembled 27 near-complete (>70%) microbial genomes through metagenomic sequencing and determined associated expression patterns through metatranscriptomic sequencing. Differential gene expression analysis revealed a shift in the central carbohydrate metabolism and the induction of metalloproteases, siderophores, and toxins in Alteromonas, Erythrobacter, Oceanicola, and Alcanivorax populations. Sugar-specific induction of virulence factors suggests a mechanistic link for the switch from a commensal to a pathogenic lifestyle, particularly relevant during increased algal cover and human-derived pollution on coral reefs. Although an explicit test remains to be performed, our data support the hypothesis that increased availability of specific sugars changes net microbial community activity in ways that increase the emergence and abundance of opportunistic pathogens, potentially contributing to coral reef degradation.

Anti-biofilm effect of 405-nm LEDs against Listeria monocytogenes in simulated ready-to-eat fresh salmon storage conditions

The objective of this study was to evaluate the anti-biofilm effect of 405-nm light-emitting diodes (LEDs) against Listeria monocytogenes in salmon exudate at 4, 15, and 25 °C, and to compare the susceptibility of LED-illuminated and non-illuminated pre-formed biofilm cells to sanitizer treatment. For the biofilm-forming scenario, stainless-steel (SS) or acrylic (AC) coupons in sterilized salmon exudate were inoculated with L. monocytogenes and then illuminated with 405-nm LEDs (26 ± 2 mW/cm2) at each temperature for 8 h. For the pre-formed biofilm scenario, L. monocytogenes biofilms were pre-formed onto each coupon at 25 °C for 24 h and subsequently illuminated at each temperature, followed by treatment with 200 ppm quaternary ammonium compound (QAC) for 10 s to compare the sensitivity of LED-illuminated biofilm cells to the sanitizer treatment. Regardless of illumination temperature, the results showed that 405-nm LED illumination significantly (P < 0.05) reduced both planktonic and biofilm cell populations on SS and AC coupons during biofilm formation. There were no significant (P ≥ 0.05) changes in the planktonic and biofilm cell populations, for the pre-formed biofilm scenario, in response to LED illumination at 4 and 15 °C. However, significant biofilm cell reductions were observed on SS and AC coupons in response to LED illumination at 25 °C for 8 h. Regardless of coupon type, LED-illuminated biofilm cells were found to be more sensitive to QAC treatment under the pre-formed biofilm scenario than non-illuminated cells. These results indicate that 405-nm LED illumination may be effective in controlling L. monocytogenes during the biofilm formation process, and at inducing sensitivity to sanitizer treatment in pre-formed biofilm cells. Thus, this study suggests the potential of LED technology in controlling L. monocytogenes biofilms during the processing and storage of ready-to-eat salmon, minimizing the chance of cross-contamination from contaminated surfaces.

Influence of l-amino acids on aggregation and biofilm formation in Azotobacter chroococcum and Trichoderma viride.

The effects of l-amino acids on growth and biofilm formation in Azotobacter chroococcum (Az) and Trichoderma viride (Tv) as single (Az, Tv) and staggered inoculated cultures (Az-Tv, Tv-Az) were investigated. A preliminary study using a set of 20 l-amino acids, identified 6 amino acids (l-Glu, l-Gln, l-His, l-Ser, l-Thr and l-Trp) which significantly enhanced growth and biofilm formation. Supplementation of these amino acids at different concentrations revealed that 40mmoll-1 was most effective. l-Glu and l-Gln favoured planktonic growth in both single and in staggered inoculated cultures, while l-Trp and l-Thr, enhanced aggregation and biofilm formation. Addition of l-Glu or l-Gln increased carbohydrate content and planktonic population. Principal component analysis revealed the significant role of proteins in growth and biofilm formation, particularly with supplementation of l-Trp, l-Thr and l-Ser. Azotobacter was found to function better as biofilm under staggered inoculated culture with Trichoderma. The results illustrate that amino acids play crucial roles in microbial biofilm formation, by influencing growth, aggregation and carbohydrates synthesized. The differential and specific roles of amino acids on biofilm formation are of significance for agriculturally important micro-organisms that grow as biofilms, colonize and benefit the plants more effectively.

Ecological Stoichiometry of Ocean Plankton.

Marine plankton elemental stoichiometric ratios can deviate from the Redfield ratio (106C:16N:1P); here, we examine physiological and biogeochemical mechanisms that lead to the observed variation across lineages, regions, and seasons. Many models of ecological stoichiometry blend together acclimative and adaptive responses to environmental conditions. These two pathways can have unique molecular mechanisms and stoichiometric outcomes, and we attempt to disentangle the two processes. We find that interactions between environmental conditions and cellular growth are key to understanding stoichiometric regulation, but the growth rates of most marine plankton populations are poorly constrained. We propose that specific physiological mechanisms have a strong impact on plankton and community stoichiometry in nutrient-rich environments, whereas biogeochemical interactions are important for the stoichiometry of the oligotrophic gyres. Finally, we outline key areas with missing information that is needed to advance understanding of the present and future ecological stoichiometry of ocean plankton.

Influence of feeding, periphyton and compost application on the performances of striped grey mullet (Mugil cephalus L.) fingerlings in fertilized brackishwater ponds

To evaluate the effects of different management systems on performances of grey mullet (Mugil cephalus L.) fingerlings, a 120-day experimental trial was conducted in twelve brackishwater ponds (600m2 each). Rearing management systems assessed were: fertilization alone (FR), combined fertilization-feeding (FF), fertilization-periphyton (FP) and fertilization-compost application (FC) in triplicate ponds. Soaked mustard cake was used as a fertilizer @ 100kgha−1 at 15-day intervals in all the treatment ponds. Formulated crumble diet containing 29.7% protein and 4.9% lipid was used as a supplementary feed in FF. Bamboo poles were used as substrates (equivalent to 10% of pond surface area) to facilitate periphyton growth in FP and composted aquatic weed was applied @ 500kgha−1 in FC at monthly intervals. Ponds were stocked with grey mullet fry (3.36±0.32g/63.70±4.61mm) at 30,000numberha−1. The experiment revealed significant differences in most of the water quality parameters among the four treatments. In FP ponds, a significant reduction (P<0.05) in inorganic nitrogen and phosphorous, chlorophyll-a contents, and plankton population was observed. The highest fish growth (28.39±1.94g) and survival (94.3±4.2%) were recorded in FP followed by in FF, FC and FR (P<0.05). A significantly higher total fish biomass (P<0.05) was obtained in FP (803±29kgha−1) followed by in FF (730±37), FC (507±33) and FR (362±22). Condition factor (K) and isometric exponent (b) of length-weight relationship indicated that fingerlings were in better condition with isometric growth (K=1.37±0.13; b=3.01±0.12) in FP. Inferior condition with allometric growth was observed in FR, FF and FC systems. These results suggest that periphyton based system can be an appropriate rearing technique for grey mullet fingerling production in brackishwater fertilized ponds as an environment-friendly and sustainable practice.

Biofilm formation and disinfectant resistance of Salmonella sp. in mono- and dual-species with Pseudomonas aeruginosa.

This study aimed to evaluate the biofilm formation and disinfectant resistance of Salmonella cells in mono- and dual-species biofilms with Pseudomonas aeruginosa, and to investigate the role of extracellular polymeric substances (EPS) in the protection of biofilms against disinfection treatment. The populations of Salmonella in mono- or dual-species biofilms with P. aeruginosa on stainless steel (SS) coupons were determined before and after exposure to commercial disinfectant, 50μgml-1 chlorine or 200μgml-1 Ecolab® Whisper™ V (a blend of four effective quaternary ammonium compounds (QAC)). In addition, EPS amount from biofilms was quantified and biofilm structures were observed using scanning electron microscopy (SEM). Antagonistic interactions between Salmonella and P. aeruginosa resulted in lower planktonic population level of Salmonella, and lower density in dual-species biofilms compared to mono-species biofilms. The presence of P. aeruginosa significantly enhanced disinfectant resistance of S. Typhimurium and S. Enteritidis biofilm cells for 2days, and led to an average of 50% increase in polysaccharides amount in dual-species biofilms than mono-species biofilms of Salmonella. Microscopy observation showed the presence of large microcolonies covered by EPS in dual-species biofilms but not in mono-species ones. The presence of P. aeruginosa in dual-species culture inhibited the growth of Salmonella cells in planktonic phase and in biofilms, but protected Salmonella cells in biofilms from disinfection treatment, by providing more production of EPS in dual-species biofilms than mono-species ones. This study provides insights into inter-species interaction, with regard to biofilm population dynamics and disinfectant resistance. Thus, a sanitation protocol should be designed considering the protective role of secondary species to pathogens in biofilms on SS surface which has been widely used at food surfaces and manufacturers.

Pseudomonas aeruginosa Alters Staphylococcus aureus Sensitivity to Vancomycin in a Biofilm Model of Cystic Fibrosis Infection.

ABSTRACTThe airways of cystic fibrosis (CF) patients have thick mucus, which fosters chronic, polymicrobial infections. Pseudomonas aeruginosa and Staphylococcus aureus are two of the most prevalent respiratory pathogens in CF patients. In this study, we tested whether P. aeruginosa influences the susceptibility of S. aureus to frontline antibiotics used to treat CF lung infections. Using our in vitro coculture model, we observed that addition of P. aeruginosa supernatants to S. aureus biofilms grown either on epithelial cells or on plastic significantly decreased the susceptibility of S. aureus to vancomycin. Mutant analyses showed that 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO), a component of the P. aeruginosa Pseudomonas quinolone signal (PQS) system, protects S. aureus from the antimicrobial activity of vancomycin. Similarly, the siderophores pyoverdine and pyochelin also contribute to the ability of P. aeruginosa to protect S. aureus from vancomycin, as did growth under anoxia. Under our experimental conditions, HQNO, P. aeruginosa supernatant, and growth under anoxia decreased S. aureus growth, likely explaining why this cell wall-targeting antibiotic is less effective. P. aeruginosa supernatant did not confer additional protection to slow-growing S. aureus small colony variants. Importantly, P. aeruginosa supernatant protects S. aureus from other inhibitors of cell wall synthesis as well as protein synthesis-targeting antibiotics in an HQNO- and siderophore-dependent manner. We propose a model whereby P. aeruginosa causes S. aureus to shift to fermentative growth when these organisms are grown in coculture, leading to reduction in S. aureus growth and decreased susceptibility to antibiotics targeting cell wall and protein synthesis.

Reduced susceptibility to disinfectants of Acinetobacter baumannii biofilms on glass and ceramic.

The aim of this study was to determine the susceptibility of hospital and environmental Acinetobacter baumannii isolate biofilms on ceramics and glass to common disinfectants benzalkonium chloride and chlorhexidine. For this purpose we developed a new method for biofilm cultivation and quantification on ceramics. The biofilm bacteria were more resistant to disinfectants than the planktonic populations, as more than 50 % of the biofilm population and none of the planktonic population survived 5-minute exposure. Furthermore, biofilm populations on ceramic tiles were significantly more resistant than those on glass coverslips, even though the amount of biofilm was practically the same on ceramics and glass. The reason for reduced susceptibility of A. baumannii biofilms on ceramics may be related to surface/disinfection interactions. Our findings suggest that biofilms on ceramic surfaces can be an important source of A. baumannii infection in hospital environments.

Quantifying nitrogen assimilation rates of individual phytoplankton species and plankton groups during harmful algal blooms via sorting flow cytometry

AbstractWhile 15N‐labeled nitrogen (N) compounds have been used to quantify N uptake rates by plankton communities for decades, accurately ascribing those rates to individual populations or species has been a challenge. Here, we apply sorting flow cytometry combined with species‐specific immuno‐detection of a harmful alga, Aureococcus anophagefferens, to contrast the nutritional ecology of this alga with co‐occurring picoplankton (picoeukaryotes, cyanobacteria, heterotrophic bacteria) during brown tides. The method was iteratively refined to yield close agreement (85–101%) between plankton community 15N uptake quantified via traditional filtration and this novel sorting method. Sorting of plankton revealed that the δ15N values of A. anophagefferens and phycocyanin‐containing cyanobacteria were more enriched (∼ 10‰) than the values of other picoeukaryotes and heterotrophic bacteria that decreased to &lt; 0‰ after A. anophagefferens abundance declined, suggesting that these plankton utilized isotopically lighter nitrogen sources (e.g., recycled nutrients or fertilizer). A. anophagefferens utilized multiple forms of nitrogen (e.g., nitrate, ammonium, urea) during blooms and their uptake rates of ammonium and urea were highest during blooms. However, A. anophagefferens urea uptake rates on a per cell basis were fivefold faster than all other groups, affirming the nutritionally strategic uptake of urea to fuel brown tides. This study presents a novel approach to successfully sort a single algal species from a plankton community for the purpose of assessing nitrogen uptake and highlights a promising and powerful approach for investigating and contrasting the nutritional ecology of bloom‐causing species and co‐occurring plankton populations during harmful algal blooms.