Antifouling activity of symbiotic bacteria from sponge Aplysina gerardogreeni

A key area in marine antifoulant research is the discovery of new environmentally friendly solutions that prevent biofilm formation and associated biocorrosion. Taking into consideration the natural mechanisms of marine organisms to protect against epibiosis, new biomimetic solutions can be utilised against biofouling, and marine bacteria are promising agents. Therefore, the goal of this study was to identify cultivable bacteria with antifouling (AF) activity associated with the sponge Aplysina gerardogreeni. A collection of 63 bacteria was isolated, and the organic extracts were assayed against various microfouler strains (16 bacteria and five microalgae). The results showed that 87% of bacterial extracts were active against the microfoulers tested. Sixteen of them can be considered to possess AF potential and belong to the genera Bacillus, Micrococcus, Paracoccus, Pseudobacter, Pseudovibrio, Psychrobacter, Staphylocuccus and Terribacillus. Bioactivity showed temporal variations; the highest activity was in February and June and the lowest in October. Bacillus bacteria were dominant and showed AF activities throughout the year. The results revealed those marine bacteria sponge-associated and the genus Bacillus in particular, are promising AF agents.     

Methods of downstream processing for the production of biodiesel from microalgae

Despite receiving increasing attention during the last few decades, the production of microalgal biofuels is not yet sufficiently cost-effective to compete with that of petroleum-based conventional fuels. Among the steps required for the production of microalgal biofuels, the harvest of the microalgal biomass and the extraction of lipids from microalgae are two of the most expensive. In this review article, we surveyed a substantial amount of previous work in microalgal harvesting and lipid extraction to highlight recent progress in these areas. We also discuss new developments in the biodiesel conversion technology due to the importance of the connectivity of this step with the lipid extraction process. Furthermore, we propose possible future directions for technological or process improvements that will directly affect the final production costs of microalgal biomass-based biofuels.     

Structures and functions of algal glycans shape their capacity to sequester carbon in the ocean

Algae synthesise structurally complex glycans to build a protective barrier, the extracellular matrix. One function of matrix glycans is to slow down microorganisms that try to enzymatically enter living algae and degrade and convert their organic carbon back to carbon dioxide. We propose that matrix glycans lock up carbon in the ocean by controlling degradation of organic carbon by bacteria and other microbes not only while algae are alive, but also after death. Data revised in this review shows accumulation of algal glycans in the ocean underscoring the challenge bacteria and other microbes face to breach the glycan barrier with carbohydrate active enzymes. Briefly we also update on methods required to certify the uncertain magnitude and unknown molecular causes of glycan-controlled carbon sequestration in a changing ocean.     

Engineered chlorophyll catabolism conferring predator resistance for microalgal biomass production

Production of valuable compounds including biofuels and pharmaceutical precursors derived from microalgae has garnered significant interest. Stable production of algal biomass is essential to make the microalgal industry commercially feasible. However, one of the largest issues is severe biological contamination by predators grazing the algal biomass, resulting in the crash of outdoor cultures. In the present study, we propose a novel engineering strategy for microalgae to cope with predators. The overexpression of plant chlorophyllase (CLH) in a microalga resulted in the enhancement of resistance to the predator. This result supported our hypothesis that CLH promotes chlorophyll breakdown in the chloroplasts of the microalgae when they are digested by the predator, generating the phototoxic catabolite chlorophyllide that damages the predator. To the best of our knowledge, this is the first study to establish predator-resistant microalgae by enhancing the CLH activity.     

Auxin and cytokinin synergism augmenting biomass and lipid production in microalgae Desmodesmus sp. JS07

Microalgae are considered as a promising resource for biodiesel. Nevertheless, their commercial exploitation necessitates considerable impetus towards the development of approaches for increased biomass and lipid production. The present work elucidates the impact of exogenously supplemented auxins, i.e., indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and indole-3-propionic acid (IPA) and cytokinins, i.e., benzylaminopurine (BAP) and thidiazuron (TDZ) on biomass, lipid content and fatty acid profile of Desmodesmus sp. JS07. Among auxins, IBA improved the biomass and lipid content up to 1.96 ± 0.11 g/L and 34.88 ± 3.87 %, respectively while BAP among cytokinins increased the biomass and lipid content up to 1.88 ± 0.061 g/L and 31.84 ± 1.33 % respectively. Further, the cumulative impact of IBA (10 mg/L) and BAP (5 mg/L) resulted in their synergistic effect by stimulating biomass and lipid content up to 2.34 ± 0.032 g/L and 42.43 ± 1.88 % respectively. Auxins stimulated the superoxide dismutase activity, and cytokinins increased the enzymes (catalase and ascorbate peroxidase), scavenging reactive oxidative species, thereby regulating ROS homeostasis in microalgae. A significant alteration in the fatty acid profile owing to the type and dosage of phytohormones was detected. Hence, the strategy employing phytohormones could prove to be a meaningful approach for biofuel production.     

The odyssey of new production

In studies of primary production of the open ocean, the measurement of new production is often considered a measure of the degree of eutrophication. Because of new research this is questionable, which in our opinion, calls for a refinement to the original concept. We believe that the measure of variable fluorescence is pivotal to a new understanding. Our research enforces the growing conviction that the measurement of Fv/Fm can be interpreted as an analogue for nutrient stress. We measured variable fluorescence in axenic cultures at the CCMP at the Bigelow Laboratory. The Fv/Fm of cultures, upon transfer to new media reached a maximum followed by a decline after approximately 30 days. The rate of decline does not appear to be species specific. Most of the clones remained relatively high after 30 days. The high Fv/Fm values observed in nutrient-replete cultures are not characteristic of the oligotrophic surface waters off Florida and the Bahamas, but are approached in the eutrophic waters of the Gulf of Maine. In contrast, Fv/Fm measurements of attached macroalgae and coral zooxanthellae are characteristically much higher than microalgae of either oligotrophic or eutrophic regions. Accordingly, we advance the case for interpretation of Fv/Fm in terms of nutrient stress in ecological studies and advocate that the old concept of new production should be modified.     

UV damage to plant life in a photobiologically dynamic environment: the case of marine phytoplankton

The effect of UV-B radiation on growth of marine phytoplankton was investigated in relation to DNA damage induced by a range of biologically effective doses (BEDs). Emiliania huxleyi (Prymnesiophyceae) was chosen as a model organism of the ocean's phytoplankton because of its importance in global biogeochemical cycling of carbon and sulphur, elements that influence the world's climate as components of the trace gases carbon dioxide (CO₂) and dimethylsulfide (DMS). A marine diatom, Cyclotella, was studied for its capacity to repair the DNA damage, quantified as thymine dimers by the application of a monoclonal antibody against these photoproducts. DNA repair was shown to be complete after just a few hours of exposure to visible light; the repair rate increased with PAR intensity. E. huxleyi appeared to be most sensitive to UV-B radiation: growth was already affected above a dose of 100 J m^-2 d^-1 (biologically effective radiation, weighted with Setlow's DNA action spectrum), probably through effects on the cell cycle related to damage to nuclear DNA: mean specific growth rates were inversely correlated with thymine dimer contents in cells. Near the ocean's surface UV-B radiation conditions that induce the changes observed by us in cultures can be expected during the growing season of phytoplankton, not only in the tropics but also at higher latitudes. Nevertheles, blooms of species such as E. huxleyi are often excessive in the field. It is suggested that exposure duration of cells near the surface of the ocean can be shorter than our artificial 3 h in the laboratory due to vertical mixing, a phenomenon that is typical for the ocean's upper 50–100 m. When mixing reaches depths greater than the layer where most UV-B is attenuated, negative effects on cells through UV-A-induced inhibition of photosynthesis may prevail over DNA damage, the action spectrum of which has been shown to be limited to the UV-B part of the spectrum. Moreover, the radiation wavelengths that induce DNA damage repair (UV-A and visible) are attenuated vertically much less than UV-B. The photobiological situation in the upper ocean is much more complicated than on land, and effects of UV radiation on plankton biota can only be modelled realistically here when both the spectrally differential attenuation in the UV and visual part of the spectrum and the rate of vertical mixing are taken into account. Action spectra of both damage and repair of DNA and of photosynthesis inhibition of representative microalgal species are the second conditio sine qua non if we want to predict the effect of stratospheric ozone depletion on marine phytoplankton performance.