Growth rate hypothesis and efficiency of protein synthesis under different sulphate concentrations in two green algae

Phosphorus-supplemented seawater-wastewater cyclic system for microalgal cultivation: Production of high-lipid and high-protein algae

The reuse of wastewater after seawater cultivation is critically important. In this study, a phosphorus-supplemented seawater-wastewater cyclic system (PSSWCS) based on Chlorella pyrenoidosa SDEC-35 was developed. With the addition of phosphorus, the algal biomass and the ability to assimilate nitrogen and carbon were improved. At the nitrogen to phosphorus ratio of 20:1, the biomass productivity per mass of nitrogen reached 3.6 g g-1 (N) day-1 in the second cycle. After the third cycle the protein content reached 35.7% of dry mass, and the major metabolic substances in PSSWCS reached the highest content level of 89.5% (35.7% protein, 38.3% lipid, and 15.5% carbohydrate). After the fourth cycle the lipid content maintained at 40.1%. Furthermore, 100.0% recovery of wastewater in PSSWCS increased the nitrogen and carbon absorption to 15.0 and 396.8 g per tonne of seawater. This study achieved seawater-wastewater recycle and produced high-lipid and high-protein algae by phosphorus addition.

Marine phytoplankton downregulate core photosynthesis and carbon storage genes upon rapid mixed layer shallowing

Marine phytoplankton are a diverse group of photoautotrophic organisms and key mediators in the global carbon cycle. Phytoplankton physiology and biomass accumulation are closely tied to mixed layer depth, but the intracellular metabolic pathways activated in response to changes in mixed layer depth remain less explored. Here, metatranscriptomics was used to characterize the phytoplankton community response to a mixed layer shallowing (from 233 to 5 m) over the course of two days during the late spring in the Northwest Atlantic. Most phytoplankton genera downregulated core photosynthesis, carbon storage, and carbon fixation genes as the system transitioned from a deep to a shallow mixed layer and shifted towards catabolism of stored carbon supportive of rapid cell growth. In contrast, phytoplankton genera exhibited divergent transcriptional patterns for photosystem light harvesting complex genes during this transition. Active virus infection, taken as the ratio of virus to host transcripts, increased in the Bacillariophyta (diatom) phylum and decreased in the Chlorophyta (green algae) phylum upon mixed layer shallowing. A conceptual model is proposed to provide ecophysiological context for our findings, in which integrated light limitation and lower division rates during transient deep mixing are hypothesized to disrupt resource-driven, oscillating transcript levels related to photosynthesis, carbon fixation, and carbon storage. Our findings highlight shared and unique transcriptional response strategies within phytoplankton communities acclimating to the dynamic light environment associated with transient deep mixing and shallowing events during the annual North Atlantic bloom.

Biochemical Evaluation of Agaricus and Pleurotus Strains in Batch Cultures for Production Optimization of Valuable Metabolites

The production of various biochemical compounds such as proteins, glucans and glucanases, from the mycelium of four strains of Basidiomycetes species, Agaricus bisporus, Agaricus subrufescens, Pleurotus eryngii and Pleurotus ostreatus, during batch culture in shaking flasks, was studied. Fungi were cultured for 26 days in defined media with glucose as carbon source and were primarily evaluated for their ability to consume glucose and produce mycelial mass and intracellular polysaccharides (IPS). Results showed that on the 26th day of cultivation, P. ostreatus produced the maximum biomass (16.75 g/L), whereas P. eryngii showed the maximum IPS concentration (3.82 g/L). All strains presented a similar pattern in total protein production, with A. bisporus having the highest percentage of total proteins (36%, w/w). The calculated correlation coefficients among ribonucleic acid (RNA) vs. biomass (0.97) and RNA vs. protein (0.97) indicated a very strong relation between RNA and biomass/protein synthesis. The studied strains exhibited an increase in total glucan and glucanase (β-1,6) production during cultivation, with A. bisporus reaching the highest glucan percentage (8%, w/w) and glucanase activity (12.7 units/g biomass). Subsequently, processed analytical data were used in contour-graph analysis for data extrapolation to optimize future continuous culture.

Coupling of myo-inositol with salinity regulates ethylene-induced microalgal lipid hyperproduction in molasses wastewater

With the goal of cost-effective and high-efficient microalgae-based biodiesel production, this study evaluated the feasibility of the joint strategy concerning myo-inositol (MI) and salinity stress on lipid productivity of Monoraphidium sp. QLY-1 in molasses wastewater (MW). The maximal lipid productivity (147.79 mg L^-1 d^-1) was obtained under combined 0.5 g L^-1 MI and 10 g L^-1 NaCl treatment, which was 1.40-fold higher than the control. Meanwhile, the nutrients removal from MW was markedly increased under MI-NaCl treatment. Moreover, exogenous MI upregulated key lipogenic genes' expressions, activated autophagic activity and ethylene (ET) signaling, and ultimately alleviated the salinity-induced damage via reactive oxygen species (ROS) signaling. Further pharmacologic experiment confirmed the indispensable role of ET in the lipogenesis progress under the combined treatment. These data demonstrated the combined salinity stress and MI treatment to be capable for lipid hyperproduction and wastewater nutrients removal, which contributes to practically integrating the microalgae cultivation with wastewater treatment.

Shuffling between Cladocopium and Durusdinium extensively modifies the physiology of each symbiont without stressing the coral host

As sea surface temperatures increase, many coral species that used to harbour symbionts of the genus Cladocopium have become colonized with the thermally tolerant genus, Durusdinium. Here, we asked how gene expression in the symbionts of one genus changes depending on the abundance of another symbiont genus within the same coral host, and what effect this interaction has on the host. Symbiont gene expression was overwhelmingly driven by whether the genus was the minority or the majority within the host, which affected 79% (Durusdinium) and 96% (Cladocopium) of all genes. Particularly strong effects in both genera were observed for photosynthesis components (upregulated in the minority state) and proteins putatively associated with cell motility (upregulated in the majority state). Importantly, there was no distinct gene expression signature associated with the mixed symbiosis state when both genera were represented in comparable proportions within the host, which could lead to more intense competition. The mixed symbiosis was also not associated with elevated host stress: in fact, after heat treatment, stress signatures were the lowest in mixed-symbiosis corals compared to both Cladocopium- and Durusdinium-dominated corals. In conclusion, during shuffling between Cladocopium and Durusdinium both symbiont genera go through extensive and largely reciprocal physiological transitions, but there is no evidence of intensifying antagonistic interactions that are detrimental to the host. Unless the mixed-symbiosis corals in this study are not representative of the typical transition between Cladocopium and Durusdinium, the process of shuffling from one symbiont genus to another appears to be cost-free for the coral host, and even appears to be associated with lower stress susceptibility. This raises optimism for the future corals, which will probably have to rely on symbiont shuffling more and more to withstand environmental challenges.

Biomass composition explains fruit relative growth rate and discriminates climacteric from non-climacteric species

Fleshy fruits are very varied, whether in terms of their composition, physiology, or rate and duration of growth. To understand the mechanisms that link metabolism to phenotypes, which would help the targeting of breeding strategies, we compared eight fleshy fruit species during development and ripening. Three herbaceous (eggplant, pepper, and cucumber), three tree (apple, peach, and clementine) and two vine (kiwifruit and grape) species were selected for their diversity. Fruit fresh weight and biomass composition, including the major soluble and insoluble components, were determined throughout fruit development and ripening. Best-fitting models of fruit weight were used to estimate relative growth rate (RGR), which was significantly correlated with several biomass components, especially protein content (R=84), stearate (R=0.72), palmitate (R=0.72), and lignocerate (R=0.68). The strong link between biomass composition and RGR was further evidenced by generalized linear models that predicted RGR with R-values exceeding 0.9. Comparison of the fruit also showed that climacteric fruit (apple, peach, kiwifruit) contained more non-cellulosic cell-wall glucose and fucose, and more starch, than non-climacteric fruit. The rate of starch net accumulation was also higher in climacteric fruit. These results suggest that the way biomass is constructed has a major influence on performance, especially growth rate.

A tale of two eras: Phytoplankton composition influenced by oceanic paleochemistry

We report the results of simple experiments which support the hypothesis that changes in ocean chemistry beginning in the Mesozoic Era resulted in an increase in the nutritional quality per mole of C and per cell of planktonic algal biomass compared to earlier phytoplankton. We cultured a cyanobacterium, a diatom, a dinoflagellate, and a green alga in media mimicking aspects of the chemistry of Palaeozoic and Mesozoic-Cenozoic oceans. Substantial differences emerged in the quality of algal biomass between the Palaeozoic and Mesozoic-Cenozoic growth regimes; these differences were strongly affected by interspecific interactions (i.e., the co-existence of different species alters responses to the chemistry of the medium). The change was in the direction of a Mesozoic-Cenozoic biomass enriched in protein per mole C, although cells contained less carbon overall. This would lead to a lower C:N ratio. On the assumption that Mesozoic-Cenozoic grazers' assimilation of total C was similar to that of their earlier counterparts, their diet would be stoichiometrically closer to their C:N requirement. This, along with an increase in mean cell size among continental shelf phytoplankton, could have helped to facilitate observed evolutionary changes in the Mesozoic marine fauna. In turn, increased grazing pressure would have operated as a selective force for the radiation of phytoplankton clades better equipped with antigrazing capabilities (sensu lato), as found widely in phytoplankton with biomineralization. Our results emphasize potential links between changing seawater chemistry, increased predation pressure and the rise to ecological dominance of chlorophyll a+c algae in Mesozoic oceans. The experiments also suggest a potential role for ocean chemistry in changes of marine trophic structure from the Palaeozoic to the later Mesozoic Era.

Phytoplankton growth rate modelling: can spectroscopic cell chemotyping be superior to physiological predictors?

Climate change has a strong impact on phytoplankton communities and water quality. However, the development of robust techniques to assess phytoplankton growth is still in progress. In this study, the growth rate of phytoplankton cells grown at different temperatures was modelled based on conventional physiological traits (e.g. chlorophyll, carbon and photosynthetic parameters) using the partial least square regression (PLSR) algorithm and compared with a new approach combining Fourier transform infrared-spectroscopy and PLSR. In this second model, it is assumed that the macromolecular composition of phytoplankton cells represents an intracellular marker for growth. The models have comparable high predictive power (R² > 0.8) and low error in predicting new observations. Interestingly, not all of the predictors present the same weight in the modelling of growth rate. A set of specific parameters, such as non-photochemical fluorescence quenching (NPQ) and the quantum yield of carbon production in the first model, and lipid, protein and carbohydrate contents for the second one, strongly covary with cell growth rate regardless of the taxonomic position of the phytoplankton species investigated. This reflects a set of specific physiological adjustments covarying with growth rate, conserved among taxonomically distant algal species that might be used as guidelines for the improvement of modern primary production models. The high predictive power of both sets of cellular traits for growth rate is of great importance for applied phycological studies. Our approach may find application as a quality control tool for the monitoring of phytoplankton populations in natural communities or in photobioreactors.

The use of NH4+ rather than NO3- affects cell stoichiometry, C allocation, photosynthesis and growth in the cyanobacterium Synechococcus sp. UTEX LB 2380, only when energy is limiting

The assimilation of N-NO₃^- requires more energy than that of N-NH₄⁺ . This becomes relevant when energy is limiting and may impinge differently on cell energy budget depending on depth, time of the day and season. We hypothesize that N-limited and energy-limited cells of the oceanic cyanobacterium Synechococcus sp. differ in their response to the N source with respect to growth, elemental stoichiometry and carbon allocation. Under N limitation, cells retained almost absolute homeostasis of elemental and organic composition, and the use of NH₄⁺ did not stimulate growth. When energy was limiting, however, Synechococcus grew faster in NH₄⁺ than in NO₃^- and had higher C (20%), N (38%) and S (30%) cell quotas. Furthermore, more C was allocated to protein, whereas the carbohydrate and lipid pool size did not change appreciably. Energy limitation also led to a higher photosynthetic rate relative to N limitation. We interpret these results as an indication that, under energy limitation, the use of the least expensive N source allowed a spillover of the energy saved from N assimilation to the assimilation of other nutrients. The change in elemental stoichiometry influenced C allocation, inducing an increase in cell protein, which resulted in a stimulation of photosynthesis and growth.

Toward facilitating microalgae cope with effluent from anaerobic digestion of kitchen waste: the art of agricultural phytohormones

BACKGROUND

Although numerous studies have used wastewater as substitutes to cultivate microalgae, most of them obtained weaker algal viability than standard media. Some studies demonstrated a promotion of phytohormones on algal growth in standard media. For exploiting a strategy to improve algal biomass accumulation in effluent from anaerobic digestion of kitchen waste (ADE-KW), the agricultural phytohormones gibberellin, indole-3-acetic acid, and brassinolide (GIB) were applied to Chlorella SDEC-11 and Scenedesmus SDEC-13 at different stages of algal growth. Previous studies have demonstrated a promotion of phytohormones on algal growth in standard media, but attempts have been scarce, focusing on wastewater cultivation system. In addition, the effects of wastewater on algal morphology and ultrastructure have not been revealed so far, much less on the mechanism of the role of phytohormones on algae.

RESULTS

ADE-KW disrupted the membranes of nuclear and chloroplast in ultrastructural cell of SDEC-11, and reduced the room between chloroplast and cell membrane and increased the starch size of SDEC-13. This reduced algal growth and biocompound accumulation, but SDEC-13 had greater adaptation to ADE-KW than SDEC-11. Moreover, inoculation with an algal seed pretreated with GIB aided the adaptability and viability of algae in ADE-KW, which for SDEC-13 was even promoted to the level in BG11. GIB mitigated the inhibition of ADE-KW on algal cell division and photosynthetic pigments and apparatus, and increased lipid droplets, which might result from the change in the synthesis and the fate of nicotinamide adenine dinucleotide phosphate. GIB addition significantly promoted lipid productivity of the two algal species, following 13 mg L^-1 d^-1 of SDEC-11 in B⁺ADE-KW and especially 13 mg L^-1 d^-1 of SDEC-13 achieved during the priming of algal seed with the hormones, which is 139% higher than 5 mg L^-1 d^-1 achieved in ADE-KW control.

CONCLUSIONS

Agricultural phytohormones could be applied as a strategy for promoting biomass and biocompound accumulation of algae in ADE-KW, in which pretreatment of the algal inoculum with hormones is a unique way to help algae survive under stress. Considering our results and treatment technology for kitchen waste, a more feasible and economic plant can be built incorporating anaerobic digestion, algae cultivation with ADE-KW assisted with phytohormones, and biodiesel production.

Direct and indirect influence of sulfur availability on phytoplankton evolutionary trajectories

The sulfate facilitation hypothesis suggests that changes in ocean sulfate concentration influenced the rise to dominance of phytoplankton species of the red lineage. The mechanistic reasons for this phenomenon are not yet understood. We started to address this question by investigating the differences in S utilization by algae of the green and red lineages and in cyanobacteria cultured in the presence of either 5 mmol · L^-1 (approximately equivalent to Paleozoic ocean concentrations) or 30 mmol · L^-1 (corresponding to post-Mesozoic/extant concentrations) sulfate. The activities of the main enzymes involved in SO₄^2- assimilation changed in response to changes in growth sulfate concentration. ATP sulfurylase showed different kinetics in the various taxa, with an especially odd behavior for the dinoflagellate. Sulfate availability had a modest effect on cell organic composition. Species-specific differences in the use of some elements were instead obvious in algae grown in the presence of different sulfate concentrations, overall confirming that algae of the red lineage do better at high sulfate than algae of the green lineage. The increase in sulfate concentration may thus have had an impact on phytoplankton radiation both through changes in their enzymatic machinery and through indirect repercussion on elemental usage.

Influence of phosphorus on copper toxicity to Selenastrum gracile (Reinsch) Korshikov

Microalgae need a variety of nutrients for optimal growth and health. However, this rarely occurs in nature, and if nutrient proportions vary, biochemical changes can occur in phytoplankton community. This may result in modifications of zooplankton food quality, affecting aquatic food chains. Our aim was to investigate the toxicity of copper (Cu) to Selenastrum gracile, a common freshwater Chlorophyceae, at different physiological status induced by varying phosphorus (P) concentration in culture medium. Phosphorus was investigated at 2.3×10(-4), 1.1×10(-4), 2.3×10(-5), 4.6×10(-6) and 2.3×10(-6) mol L(-1) and Cu at six concentrations, ranging from 6.9×10(-9) mol L(-1) to 1.0×10(-7) mol L(-1) free Cu(2+) ions. To guarantee the cells would be in a physiological status that reflected the external P concentration, they were previously acclimated up to constant growth rate at each P concentration. Phosphorus acclimated cells were then exposed to Cu and toxicity was evaluated through population density, growth rates and chlorophyll a content. Free Cu(2+) ions concentrations were calculated through the chemical equilibrium model MINEQL(+). The results showed that higher Cu toxicity was obtained in P-limited than in P-replete cells, and that chlorophyll a/cell was higher in P-limited cells and excess Cu than in P-replete cells. This confirms the importance of microalgae nutritional status to withstand the negative effects of the trace metal.