scholarly journals Generalized receptor law governs phototaxis in the phytoplanktonEuglena gracilis

2015 ◽  
Vol 112 (22) ◽  
pp. 7045-7050 ◽  
Author(s):  
Andrea Giometto ◽  
Florian Altermatt ◽  
Amos Maritan ◽  
Roman Stocker ◽  
Andrea Rinaldo
Keyword(s):  
Algal Blooms ◽  
Nonlinear Response ◽  
Temporal Dynamics ◽  
Freshwater Ecosystems ◽  
Trophic Levels ◽  
Light Fields ◽  
Light Sources ◽  
Mathematical Framework ◽  
Heterogeneous Environments ◽  
Light Conditions

Phototaxis, the process through which motile organisms direct their swimming toward or away from light, is implicated in key ecological phenomena (including algal blooms and diel vertical migration) that shape the distribution, diversity, and productivity of phytoplankton and thus energy transfer to higher trophic levels in aquatic ecosystems. Phototaxis also finds important applications in biofuel reactors and microbiopropellers and is argued to serve as a benchmark for the study of biological invasions in heterogeneous environments owing to the ease of generating stochastic light fields. Despite its ecological and technological relevance, an experimentally tested, general theoretical model of phototaxis seems unavailable to date. Here, we present accurate measurements of the behavior of the algaEuglena graciliswhen exposed to controlled light fields. Analysis ofE. gracilis’ phototactic accumulation dynamics over a broad range of light intensities proves that the classic Keller–Segel mathematical framework for taxis provides an accurate description of both positive and negative phototaxis only when phototactic sensitivity is modeled by a generalized “receptor law,” a specific nonlinear response function to light intensity that drives algae toward beneficial light conditions and away from harmful ones. The proposed phototactic model captures the temporal dynamics of both cells’ accumulation toward light sources and their dispersion upon light cessation. The model could thus be of use in integrating models of vertical phytoplankton migrations in marine and freshwater ecosystems, and in the design of bioreactors.

scholarly journals Asynchrony of Gambierdiscus spp. Abundance and Toxicity in the U.S. Virgin Islands: Implications for Monitoring and Management of Ciguatera

Toxins ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 413
Author(s):  
Justin D. Liefer ◽  
Mindy L. Richlen ◽  
Tyler B. Smith ◽  
Jennifer L. DeBose ◽  
Yixiao Xu ◽  
...  
Keyword(s):  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Environmental Parameters ◽  
Virgin Islands ◽  
Coastal Communities ◽  
Trophic Levels ◽  
Us Virgin Islands ◽  
Benthic Dinoflagellates ◽  
The Mean ◽  
The U.S

Ciguatera poisoning (CP) poses a significant threat to ecosystem services and fishery resources in coastal communities. The CP-causative ciguatoxins (CTXs) are produced by benthic dinoflagellates including Gambierdiscus and Fukuyoa spp., and enter reef food webs via grazing on macroalgal substrates. In this study, we report on a 3-year monthly time series in St. Thomas, US Virgin Islands where Gambierdiscus spp. abundance and Caribbean-CTX toxicity in benthic samples were compared to key environmental factors, including temperature, salinity, nutrients, benthic cover, and physical data. We found that peak Gambierdiscus abundance occurred in summer while CTX-specific toxicity peaked in cooler months (Feb–May) when the mean water temperatures were approximately 26–28 °C. These trends were most evident at deeper offshore sites where macroalgal cover was highest year-round. Other environmental parameters were not correlated with the CTX variability observed over time. The asynchrony between Gambierdiscus spp. abundance and toxicity reflects potential differences in toxin cell quotas among Gambierdiscus species with concomitant variability in their abundances throughout the year. These results have significant implications for monitoring and management of benthic harmful algal blooms and highlights potential seasonal and highly-localized pulses in reef toxin loads that may be transferred to higher trophic levels.

Bacterial presence in polar regions associated with environment modification by chemical compounds including contaminants

2017 ◽  
Vol 25 (4) ◽  
pp. 481-491 ◽  
Author(s):  
Klaudia Kosek ◽  
Katarzyna Jankowska ◽  
Żaneta Polkowska
Keyword(s):  
Bacterial Communities ◽  
Chemical Compounds ◽  
Freshwater Ecosystems ◽  
Trophic Levels ◽  
Polar Regions ◽  
Bacterial Cells ◽  
Chemical Contamination ◽  
Climate Conditions ◽  
Biological Communities ◽  
Long Time

Microbes are omnipresent and diverse members of all biological communities. In marine and freshwater ecosystems, microorganisms form the base of the food chain supporting higher trophic levels. Even though microbes are generally thought to live in warm regions of Earth, many of them develop in cold climates. Polar regions remain relatively protected from widespread anthropogenic disturbances, which is a consequence of thier remoteness and extreme climate conditions. For a long time these regions were considered to be free from chemical contamination until scientists discovered a presence of pollutants there. Chemical contamination may induce serious disorders in the integrity of polar ecosystems influencing the growth of bacterial communities. Xenobiotics including persistent organic pollutants are transported thousands of kilometers by the air and ocean currents, and they are deposed in high-latitude regions and accumulate in all elements of the environment including bacterial communities. It is important to determine their concentration levels in bacterial cells to assess the possibility of contaminants becoming transferred to higher trophic levels; however, some species of bacteria are capable of metabolizing xenobiotics, which makes them less toxic or even removes them from the environment.

scholarly journals Automated Microscopy: Macro Language Controlling a Confocal Microscope and its External Illumination: Adaptation for Photosynthetic Organisms

2016 ◽  
Vol 22 (2) ◽  
pp. 258-263 ◽  
Author(s):  
Gábor Steinbach ◽  
Radek Kaňa
Keyword(s):  
Light Sources ◽  
Light Conditions ◽  
Photosynthetic Organisms ◽  
Automated Microscopy ◽  
Photosynthetic Microorganisms ◽  
Arduino Microcontroller ◽  
Microscopy Data ◽  
Kinetics Of ◽  
Photosynthetic Cells

AbstractPhotosynthesis research employs several biophysical methods, including the detection of fluorescence. Even though fluorescence is a key method to detect photosynthetic efficiency, it has not been applied/adapted to single-cell confocal microscopy measurements to examine photosynthetic microorganisms. Experiments with photosynthetic cells may require automation to perform a large number of measurements with different parameters, especially concerning light conditions. However, commercial microscopes support custom protocols (throughTime Controlleroffered by Olympus orExperiment Designeroffered by Zeiss) that are often unable to provide special set-ups and connection to external devices (e.g., for irradiation). Our new system combining an Arduino microcontroller with theCell⊕Findersoftware was developed for controlling Olympus FV1000 and FV1200 confocal microscopes and the attached hardware modules. Our software/hardware solution offers (1) a text file-based macro language to control the imaging functions of the microscope; (2) programmable control of several external hardware devices (light sources, thermal controllers, actuators) during imaging via the Arduino microcontroller; (3) theCell⊕Findersoftware with ergonomic user environment, a fast selection method for the biologically important cells and precise positioning feature that reduces unwanted bleaching of the cells by the scanning laser.Cell⊕Findercan be downloaded fromhttp://www.alga.cz/cellfinder. The system was applied to study changes in fluorescence intensity inSynechocystissp. PCC6803 cells under long-term illumination. Thus, we were able to describe the kinetics of phycobilisome decoupling. Microscopy data showed that phycobilisome decoupling appears slowly after long-term (>1 h) exposure to high light.

Seasonal variations of the dinoflagellate algae Noctiluca scintillans abundance in the western Arabian Sea and the northern Black Sea

2021 ◽  
Author(s):  
Sergey Piontkovski ◽  
Khalid Al Hashmi ◽  
Yuliya Zagorodnaya ◽  
Irina Serikova ◽  
Vladislav Evstigneev ◽  
...  
Keyword(s):  
Black Sea ◽  
Mixed Layer ◽  
Algal Blooms ◽  
Arabian Sea ◽  
Temporal Dynamics ◽  
The Black Sea ◽  
Northeast Monsoon ◽  
Major Peak ◽  
Noctiluca Scintillans ◽  
Upper Mixed Layer

<p>Seasonal variability is a powerful component of the spatio-temporal dynamics of plankton communities, especially in the regions with oxygen-depleted waters. The Arabian Sea and the Black Sea are typical representatives of these regions. In both, the dinoflagellate Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921, is one of the abundant plankton species which forms algal blooms. Sampling on coastal stations in the upper mixed layer by the plankton nets with the 120-140 µm mesh size was carried out in 2004-2010. Monthly data were averaged over years. A comparison of seasonal patterns of Noctiluca abundance pointed to the persistence of a bimodal seasonal cycle in both regions. The major peak was observed during spring in the Black Sea and during the winter (Northeast) monsoon in the Arabian Sea. The timing of the second (minor) peak was different over regions as well. This peak was modulated by advection of seasonally fluctuating velocity of coastal currents which transport waters enriched by nutrients by coastal upwelling. The abundance of Noctiluca of the major peak (with the concentration around 1.5*10<sup>6</sup> cells m<sup>-3</sup>) was from one to two orders as much high in the western Arabian Sea compared to the northern Black Sea. The remotely sensed chlorophyll-a concentration during the time of the major seasonal peak exhibited a fivefold difference over these regions. In terms of nutrient<sub></sub>concentration in the upper mixed layer (in particular, nitrates and silicates), a difference of about one order of magnitude was observed.</p>

scholarly journals Photosynthetic response to nitrogen source and different ratios of nitrogen and phosphorus in toxic cyanobacteria, Microcystis aeruginosa FACHB-905

2016 ◽  
Author(s):  
Guotao Peng ◽  
Zhengqiu Fan ◽  
Xiangrong Wang ◽  
Chen Chen
Keyword(s):  
Chlorophyll Fluorescence ◽  
Algal Blooms ◽  
Freshwater Ecosystems ◽  
Cyanobacterial Blooms ◽  
Photosynthetic Response ◽  
Nitrogen And Phosphorus ◽  
Ammonium Toxicity ◽  
Chlorophyll Fluorescence Parameters ◽  
Fluorescence Parameters ◽  
N Assimilation

<p>The frequent outbreak of cyanobacterial blooms has become a worldwide phenomenon in freshwater ecosystems. Studies have elucidated the close relationship between harmful algal blooms and nutrient contents, including the loading of nitrogen and the ratios of nitrogen (N) and phosphorus (P). In this study, the effect of inorganic (nitrate and ammonium) and organic (urea) nitrogen at varied N/P ratios on the <em>Microcystis</em> <em>aeruginosa</em> FACHB-905 accumulation and photosynthesis was investigated.  The optimal NO<sub>3</sub>/P in this study were 30~50 indicated by the cell abundance (4.1×10<sup>6</sup>/mL), pigment concentration (chlorophyll a 3.1 mg/L,  phycocyanin 8.3mg/L), and chlorophyll fluorescence parameters (<em>rETR</em>, <em>E<sub>k</sub>, α, φPSII</em> and <em>F<sub>v</sub>/F<sub>m</sub> </em>values), while too high NO<sub>3</sub>-N (N/P=100:1) would cause an intracellular nitrate inhibition, leading to a decrease of photosynthetic activity. In addition, low concentration of NH<sub>4</sub>-N (N/P=4:1) would favor the <em>M. aeruginosa </em>growth and photosynthesis, and high NH<sub>4</sub>/P ratio (&gt;16) would rise the ammonium toxicity of algal cells and affect the N assimilation. In urea treatments, <em>M. aeruginosa </em>responded similarly to the NH<sub>4</sub>-N treatments both in growth curves and pigment contents, and the favorable N/P ratio was between 16~30, suggested by the chlorophyll fluorescence parameters. The results demonstrated that the various chemical forms of N and N/P ratios have a significant impact on <em>Microcystis</em> abundance and photosynthesis. More work is needed to figure out the mechanism of nitrogen utilization by <em>Microcystis</em> and  the photosynthetic response to nutrient stress at the molecular level.</p>

Auto White Balance Algorithm in Digital Camera

2012 ◽  
Vol 182-183 ◽  
pp. 2080-2084
Author(s):  
Jie Li ◽  
Xue Xiang Wang ◽  
Hao Liu
Keyword(s):  
Hardware Implementation ◽  
Digital Camera ◽  
Low Complexity ◽  
Light Sources ◽  
Light Conditions ◽  
Threshold Method ◽  
White Balance ◽  
White Point ◽  
A New Technique ◽  
Better Than

Auto white balance (AWB) is an important function of digital camera. The purpose of white balance is to adjust the image to make it look like taken under standard light conditions. We present a new technique to detect the reference white point of image in this paper. This technique detects the white point of image by using dynamic threshold method, thus making it more flexible and more applicable compared to other algorithms. We test 50 images which were taken under different light sources, and find that this algorithm is better than or comparable to other algorithms both in subjective and objective aspects. At the same time, this algorithm has low complexity, and it can be easily applied to hardware implementation.

scholarly journals A First Glimpse on Cold-Adapted PCB-Oxidizing Bacteria in Edmonson Point Lakes (Northern Victoria Land, Antarctica)

Water ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 109
Author(s):  
Maria Papale ◽  
Angelina Lo Giudice ◽  
Alessandro Ciro Rappazzo ◽  
Maurizio Azzaro ◽  
Carmen Rizzo
Keyword(s):  
Human Impacts ◽  
Current Knowledge ◽  
Freshwater Ecosystems ◽  
Trophic Levels ◽  
Cold Adapted ◽  
Remote Areas ◽  
Victoria Land ◽  
Long Lifetime ◽  
Aroclor 1242 ◽  
Edmonson Point

Antarctic freshwater ecosystems are especially vulnerable to human impacts. Polychlorobiphenyls (PCBs) are persistent organic pollutants that have a long lifetime in the environment. Despite their use having either been phased out or restricted, they are still found in nature, also in remote areas. Once in the environment, the fate of PCBs is strictly linked to bacteria which represent the first step in the transfer of toxic compounds to higher trophic levels. Data on PCB-oxidizing bacteria from polar areas are still scarce and fragmented. In this study, the occurrence of PCB-oxidizing cold-adapted bacteria was evaluated in water and sediment of four coastal lakes at Edmonson Point (Northern Victoria Land, Antarctica). After enrichment with biphenyl, 192 isolates were obtained with 57 of them that were able to grow in the presence of the PCB mixture Aroclor 1242, as the sole carbon source. The catabolic gene bphA, as a proxy for PCB degradation potential, was harbored by 37 isolates (out of 57), mainly affiliated to the genera Salinibacterium, Arthrobacter (among Actinobacteria) and Pusillimonas (among Betaproteobacteria). Obtained results enlarge our current knowledge on cold-adapted PCB-oxidizing bacteria and pose the basis for their potential application as a valuable eco-friendly tool for the recovery of PCB-contaminated cold sites.

scholarly journals Dynamics of microresonator frequency comb generation: models and stability

Nanophotonics ◽  
2016 ◽  
Vol 5 (2) ◽  
pp. 231-243 ◽  
Author(s):  
Tobias Hansson ◽  
Stefan Wabnitz
Keyword(s):  
Continuous Wave ◽  
Temporal Dynamics ◽  
Frequency Comb ◽  
Modulational Instability ◽  
Theoretical Models ◽  
Light Sources ◽  
Generation Process ◽  
Modal Expansion ◽  
Frequency Combs ◽  
Comb Generation

AbstractMicroresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.

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