Ciliary beating patterns map onto a low-dimensional behavioural space

Biological systems are robust to perturbations at both the genetic and environmental levels, although these same perturbations can elicit variation in behaviour. The interplay between functional robustness and behavioural variability is exemplified at the organellar level by the beating of cilia and flagella. Cilia are motile despite wide genetic diversity between and within species, differences in intracellular concentrations of ATP and calcium, and considerable environment fluctuations in temperature and viscosity. At the same time, these perturbations result in a variety of spatio-temporal patterns that span a rich behavioural space. To investigate this behavioural space we analysed the dynamics of isolated cilia from the unicellular algae Chlamydomonas reinhardtii under many different environmental and genetic conditions. We found that, despite large changes in beat frequency and amplitude, the space of waveform shapes is low-dimensional in the sense that two features account for 80% of the observed variation. The geometry of this behavioural space accords with the predictions of a simple mechanochemical model in the low-viscosity regime. This allowed us to associate waveform shape variability with changes in only the curvature response coefficients of the dynein motors.

Bacterial lifestyle switch in response to algal metabolites

Unicellular algae, termed phytoplankton, greatly impact the marine environment by serving as the basis of marine food webs and by playing central roles in biogeochemical cycling of elements. The interactions between phytoplankton and heterotrophic bacteria affect the fitness of both partners. It is becoming increasingly recognized that metabolic exchange determines the nature of such interactions, but the underlying molecular mechanisms remain underexplored. Here, we investigated the molecular and metabolic basis for the bacterial lifestyle switch, from coexistence to pathogenicity, in Sulfitobacter D7 during its interaction with Emiliania huxleyi, a cosmopolitan bloom-forming phytoplankter. To unravel the bacterial lifestyle switch, we profiled bacterial transcriptomes in response to infochemicals derived from algae in exponential and stationary growth, which induced the Sulfitobacter D7 coexistence and pathogenicity lifestyles, respectively. We found that algal dimethylsulfoniopropionate (DMSP) was a pivotal signaling molecule that mediated the transition between the lifestyles. However, the coexisting and pathogenic lifestyles were evident only in the presence of additional algal metabolites. In the pathogenic mode, Sulfitobacter D7 upregulated flagellar motility and many transport systems, presumably to maximize assimilation of E. huxleyi-derived metabolites released by algal cells upon cell death. Specifically, we discovered that algae-produced benzoate promoted the growth of Sulfitobacter D7, and negated the DMSP-inducing lifestyle switch to pathogenicity, demonstrating that benzoate is important for maintaining the coexistence of algae and bacteria. We propose that bacteria can sense the physiological status of the algal host through changes in the metabolic composition, which will determine the bacterial lifestyle during the interactions.

Diet of European freshwater pearl mussels Margaritifera margaritifera (Mollusca: Bivalvia: Unionoida) in small river (Republic of Karelia, Russia)

The freshwater pearl mussel Margaritifera margaritifera (Linnaeus,1758) is endangered in Europe and is now listed in the Red Data Book of many countries and regions. The diet of the species in the Syskyänjoki River (a tributary of Lake Ladoga) has been studied. The contents of the intestine generally correspond to the composition of seston, and include organic detritus, filamentous and unicellular algae, fragments of invertebrates and macrophyte tissues mixed with silt and sand. The total biomass of the intestinal contents of varied from 0.8 to 30.6 mg per organism (absolutely dry weight). Margaritifera margaritifera consumes a wide range of particles, from 0.5 μm3 (bacteria and unicellular algae) to 200 000 μm3 (fragments of invertebrates and macrophyte tissues). About 90–95% (by volume) of the intestinal contents was consisted by fine organic detritus. The food composition did not differ significantly for mollusks of different sexes and size. In the intestinal contents, 63 taxa of algae were identified. The number of algal species in the content of one intestine varied from 3 to 17, with their abundance from 250 to 9560 cells per organism. The most abundant and constant in the contents of the intestines are unicellular algae. Diatoms are the most diverse, they make up 50.8% of the total number of species.

Diatomaceous Earth for Arthropod Pest Control: Back to the Future

Nowadays, we are tackling various issues related to the overuse of synthetic insecticides. Growing concerns about biodiversity, animal and human welfare, and food security are pushing agriculture toward a more sustainable approach, and research is moving in this direction, looking for environmentally friendly alternatives to be adopted in Integrated Pest Management (IPM) protocols. In this regard, inert dusts, especially diatomaceous earths (DEs), hold a significant promise to prevent and control a wide range of arthropod pests. DEs are a type of naturally occurring soft siliceous sedimentary rock, consisting of the fossilized exoskeleton of unicellular algae, which are called diatoms. Mainly adopted for the control of stored product pests, DEs have found also their use against some household insects living in a dry environment, such as bed bugs, or insects of agricultural interest. In this article, we reported a comprehensive review of the use of DEs against different arthropod pest taxa, such as Acarina, Blattodea, Coleoptera, Diptera, Hemiptera, Hymenoptera, Ixodida, Lepidoptera, when applied either alone or in combination with other techniques. The mechanisms of action of DEs, their real-world applications, and challenges related to their adoption in IPM programs are critically reported.

Symbiosis maintenance in the facultative coral, Oculina arbuscula, relies on nitrogen cycling, cell cycle modulation, and immunity

Symbiosis with unicellular algae in the family Symbiodiniaceae is common across tropical marine invertebrates. Reef-building corals offer a clear example of cellular dysfunction leading to a dysbiosis that disrupts entire ecosystems in a process termed coral bleaching. Due to their obligate symbiotic relationship, understanding the molecular underpinnings that sustain this symbiosis in tropical reef-building corals is challenging, as any aposymbiotic state is inherently coupled with severe physiological stress. Here, we leverage the subtropical, facultatively symbiotic and calcifying coral Oculina arbuscula to investigate gene expression differences between aposymbiotic and symbiotic branches within the same colonies under baseline conditions. We further compare gene ontology (GO) and KOG enrichment in gene expression patterns from O. arbuscula with prior work in the sea anemone Exaiptasia pallida (Aiptasia) and the salamander Ambystoma maculatum—both of which exhibit endophotosymbiosis with unicellular algae. We identify nitrogen cycling, cell cycle control, and immune responses as key pathways involved in the maintenance of symbiosis under baseline conditions. Understanding the mechanisms that sustain a healthy symbiosis between corals and Symbiodiniaceae algae is of urgent importance given the vulnerability of these partnerships to changing environmental conditions and their role in the continued functioning of critical and highly diverse marine ecosystems.

Phototrophs in alternative energy

The role of phototrophs is examined in alternative energy, with the main emphasis on unicellular algae. Particular attention is paid to the use of phototrophs for generating electricity using biofuel cells (plant and enzymatic biofuel cells are discussed). This study focuses on microbial fuel cells (MFC), which, along with electric power, allow obtaining biofuels and biohydrogen. This article explains the factors limiting the MFC power, and ways of overcoming them. For example, it seems promising to develop various photobioreactors in order to reduce the loss of MFC power due to overvoltage. The use of microphototrophs in MFC has led to the development of photosynthetic MFC (or PhotoMFC) through the design of autotrophic photobioreactors with forced illumination. They allow generating oxygen through photosynthesis, both in situ and ex situ, by recirculating oxygen from the photobioreactor to the cathode chamber. Artificial redox mediators can be used here, transferring electrons directly from the non-catalytic cathode to O2, formed as a result of the photosynthetic activity of algae. Biologically catalyzed cathodes have been proven to generate less power than chemical catalysts. It is noted, that the MFC installations with the micro-algae allow utilizing a wider circle of different connections – the components of effluents and withdrawals: organic acids, sugar, alcohols, fats and other substrata. The use of phototrophs for the production of biofuels is of special interest. Several different types of renewable biofuels can be produced from microalgae, the production of which can be combined with wastewater treatment, CO2 capture and production of various compounds.

Exocytosis of the silicified cell wall of diatoms involves extensive membrane disintegration

Diatoms are unicellular algae that are characterized by their silica cell walls. The silica elements form intracellularly in a membrane-bound organelle, and are exocytosed after completion. How diatoms maintain membrane homeostasis during the exocytosis of these large and rigid silica elements is a long-standing enigma. We studied membrane dynamics during cell wall formation and exocytosis in the diatom Stephanopyxis turris, using live-cell confocal microscopy and advanced electron microscopy. Our results provide detailed information on the ultrastructure and dynamics of the silicification process, showing that during cell wall formation, the organelle membranes tightly enclose the mineral phase, creating a precise mold of the delicate geometrical patterns. Surprisingly, during exocytosis of the mature silica elements, the proximal organelle membrane becomes the new plasma membrane, and the distal membranes gradually disintegrate into the extracellular space without any noticeable endocytic retrieval or extracellular repurposing. These observations suggest that diatoms evolved an extraordinary exocytosis mechanism in order to secrete their cell wall elements.

A Comparative Test on the Sensitivity of Freshwater and Marine Microalgae to Benzo-Sulfonamides, -Thiazoles and -Triazoles

The evaluation of the ecotoxicological effects of water pollutants is performed by using different aquatic organisms. The effects of seven compounds belonging to a class of widespread contaminants, the benzo-fused nitrogen heterocycles, on a group of simple organisms employed in reference ISO tests on water quality (unicellular algae and luminescent bacteria) have been assessed to ascertain their suitability in revealing different contamination levels in the water, wastewater, and sediments samples. Representative compounds of benzotriazoles, benzothiazoles, and benzenesulfonamides, were tested at a concentration ranging from 0.01 to 100 mg L−1. In particular, our work was focused on the long-term effects, for which little information is up to now available. Species-specific sensitivity for any whole family of pollutants was not observed. On average, the strongest growth rate inhibition values were expressed by the freshwater Raphidocelis subcapitata and the marine Phaeodactylum tricornutum algae. R. subcapitata was the only organism for which growth was affected by most of the compounds at the lowest concentrations. The tests on the bioluminescent bacterium Vibrio fisheri gave completely different results, further underlining the need for an appropriate selection of the best biosensors to be employed in biotoxicological studies.

Study on the Hemostasis Characteristics of Biomaterial Frustules Obtained from Diatom Navicula australoshetlandica sp.

Diatoms, known as photosynthetic unicellular algae, can produce natural biosilica frustules that exhibit great biocompatibility, superhydrophilicity, and superhemophilicity. In our study, the diatom Navicula australoshetlandica sp. was isolated from aquaculture wastewater and pretreated to obtain frustules so as to explore their hemostasis characteristics. A special “porous web” (6–8 nm) substructure in the ordered nanopores (165–350 nm) of boat-shaped diatom frustule was observed in Navicula australoshetlandica sp. using SEM and TEM analysis. Moreover, X-ray, N2 adsorption–desorption isotherms, and BET analysis showed that the diatom frustule is a mesoporous material with a surface area of 401.45 m2 g−1 amorphous silica. FTIR analysis showed that Navicula australoshetlandica sp. frustules possessed abundant OH functional groups. A low hemolysis ratio was observed for 1–5 mg mL−1 diatom frustules that did not exceed 1.55 ± 0.06%, which indicates favorable hemocompatibility. The diatom frustules exhibited the shortest clotting time (134.99 ± 7.00 s) with a hemostasis material/blood (mg/μL) ratio of 1:100, which is 1.83 times (112.32 s) shorter than that of chitosan. The activated partial thromboplastin time (aPTT) of diatom frustule was also 44.53 s shorter than the control. Our results demonstrate the potential of Navicula australoshetlandica sp. diatom frustules to be used as medical hemostasis material.

MICROORGANISMS AS INDICATORS OF SOIL QUALITY

The first bioassays for environmental monitoring were based on multicellular eukaryotic organisms, in particular fish and mammals. Because they were relatively expensive, time consuming and difficult, there was a need for alternative biological monitoring methods. It became necessary to develop and standardize toxicity tests based on prokaryotic (bacteria) or eukaryotic (protozoa, unicellular algae, yeast) microorganisms instead of higher organisms, which made it possible to quickly and inexpensively screen environmental samples for toxic and genotoxic effects. The first generation of bioassays was based on a variety of naturally sensitive microbes, while the second generation includes genetically modified microorganisms to achieve greater sensitivity and / or specificity. The next step forward was the combination of microbial cells, or parts of cells, with physicochemical detection elements, forming new integrated devices called "biosensors". The purpose of the research is to study the possibility of using microorganisms in bioindication of environmental pollution. The use of biological methods in environmental monitoring is essential to complement chemical analyzes with information on actual toxicity. Microorganisms are widely used as test objects for analyzes due to the simplicity and low cost of their cultivation. The use of microorganisms for the assessment of general toxicity or the detection of specific compounds is an important source of information on the state of the environment. Their use will significantly expand the range of environmental studies.