Lactic acid fermented microalgae and cyanobacteria as a new source of lipid reducing compounds: assessment through zebrafish Nile red fat metabolism assay and untargeted metabolomics.

Obesity is one of the most important threats to human health. Besides existing pharmacological or clinical interventions, novel effective and largely available solutions are still necessary. Among diverse natural resources, microalgae are well known for their complexity in the production of novel secondary metabolites. At the same time, lactic acid bacteria (LAB) are known for their capacity to metabolize, through fermentation, different matrices, and consequently to modify or produce new compounds with potential bioactivity. This work aimed to study the production of fermented microalgae and cyanobacteria, and to analyse their extracts in the zebrafish Nile red fat metabolism assay. Three microalgal species (Chlorella vulgaris, Chlorococcum sp. and Arthrospira platensis) were fermented with seven strains of LAB from 4 species (Lacticaseibacillus rhamnosus, Lacticaseibacillus casei, Lactobacillus delbrueckii bulgaricus and Lacticaseibacillus paracasei), derived from the UPCCO - University of Parma Culture Collection, Parma, Italy). All the selected strains were able to ferment the selected species of microalgae, and the most suitable substrate for LAB growth was Arthrospira platensis. Extracts from fermented Chlorella vulgaris and Chlorococcum sp. reduced significantly the neutral lipid reservoirs, which was not observed without fermentations. The strongest lipid reducing effect was obtained with Arthrospira platensis fermented with Lactobacillus delbrueckii bulgaricus 1932. Untargeted metabolomics identified some compound families, which could be related to the observed bioactivity, namely fatty acids, fatty amides, triterpene saponins, chlorophyll derivatives and purine nucleotides. This work opens up the possibility of developing novel functional foods or food supplements based on microalgae, since lactic acid fermentation enhanced the production of bioactive compounds with lipid reducing activities.

Investigation of dissolved organic matter's influence on the toxicity of cadmium to the cyanobacterium Microcystis aeruginosa by biochemical and molecular assays.

Rapid economic development has increased the accumulation of dissolved organic matter (DOM) and heavy metals in aquatic environments. In addition, Microcystis aeruginosa can cause the outbreak of cyanobacteria bloom and can produce microcystin, which poses a threat to human water safety. Therefore, this study analyzed the biochemical and molecular assays of DOM (0, 1, 3, 5, 8, 10 mg C L-1) extracted from four different sources on the toxicity of cadmium (Cd) to M. aeruginosa. The results showed that the addition of different concentrations of DOM from sediment, biochar, and humic acid alleviated the toxicity of Cd to M. aeruginosa. But the addition of rice hulls DOM at high concentrations (8 and 10 mg L-1) significantly reduced the normal growth and metabolic activities of M. aeruginosa. DOM from four different sources promoted the expression level of microcystin-related gene mcyA and the production of microcystin-leucine-arginine (MC-LR), and mcyA was positively correlated with MC-LR. DOM from biochar, sediment, and humic acid were able to bind Cd through complexation. The results will help to understand the toxic effects of heavy metals on toxic-producing cyanobacteria in the presence of DOM, and provide certain reference for the evaluation of water environmental health.

Ecotoxicological assessment of guanitoxin-producing cyanobacteria in Danio rerio and Daphnia similis.

Anthropogenic activity has dramatically deteriorated aquatic ecosystems in recent years. Such environmental alterations could change the primary producers' composition, exacerbating the proliferation of harmful microorganisms such as cyanobacteria. Cyanobacteria can produce several secondary metabolites, including guanitoxin, a potent neurotoxin and the only naturally occurring anticholinesterase organophosphate ever reported in the literature. Therefore, this study investigated the acute toxicity of guanitoxin-producing cyanobacteria Sphaerospermopsis torques-reginae (ITEP-024 strain) aqueous and 50% methanolic extracts in zebrafish (Danio rerio) hepatocytes (ZF-L cell line), zebrafish embryos (fish embryo toxicity - FET) and specimens of the microcrustacean Daphnia similis. For this, hepatocytes were exposed to 1-500 mg/L of the ITEP-024 extracts for 24 h, the embryos to 31.25-500 mg/L for 96 h, and D. similis to 10-3000 mg/L for 48 h. Non-target metabolomics was also performed to analyze secondary metabolites produced by the ITEP-024 using LC-MS/MS. Metabolomics indicated the guanitoxin presence just in the aqueous extract of the ITEP-024 and the presence of the cyanopeptides namalides, spumigins, and anabaenopeptins in the methanolic extract. The aqueous extract decreased the viability of zebrafish hepatocytes (EC(I)50(24h) = 366.46 mg/L), and the methanolic extract was not toxic. FET showed that the aqueous extract (LC50(96) = 353.55 mg/L) was more toxic than the methanolic extract (LC50(96) = 617.91 mg/L). However, the methanolic extract had more sublethal effects, such as abdominal and cardiac (cardiotoxicity) edema and deformation (spinal curvature of the larvae). Both extracts immobilized daphnids at the highest concentration analyzed. However, the aqueous extract was nine times more lethal (EC(I)50(48h) = 108.2 mg/L) than the methanolic extract (EC(I)50(48h) = 980.65 mg/L). Our results showed an imminent biological risk for aquatic fauna living in an ecosystem surrounded by ITEP-024 metabolites. Our findings thus highlight the urgency of understanding the effects of guanitoxin and cyanopeptides in aquatic animals.

State-of-the-art review on the ecotoxicology, health hazards, and economic loss of the impact of microcystins and their ultrastructural cellular changes.

Cyanobacteria are ubiquitously globally present in both freshwater and marine environments. Ample reports have been documented by researchers worldwide for pros and cons of cyanobacterial toxins. The implications of cyanobacterial toxin on health have received much attention in recent decades. Microcystins (MCs) represent the unique class of toxic metabolites produced by cyanobacteria. Although the beneficial aspects of cyanobacterial are numerous, the deleterious effect of MCs overlooked. Several studies on MCs evidently reported that MCs exhibit a plethora of harmful effect on animals, plants, and cell lines. Accordingly, numerous histopathological studies have also found that MCs cause detrimental effects to cells by damaging cellular organelles, including nuclear envelope, Golgi apparatus, endoplasmic reticulum, mitochondria, plastids, flagellum, pilus membrane structures and integrity, vesicle structures, and autolysosomes and autophagosomes. Such ultrastructural cellular damages holistically influence the morphological, biochemical, physiological, and genetic status of the host. Indeed, MCs have also been found to cause the deleterious effect to different animals and plants. Such deleterious effects of MCs have greater impact on agriculture, public health which in turn influences ecotoxicology and economic consequences. The impairments correspond to oxidative stress, organ failure, carcinogenesis, aquaculture loss, with an emphasis for blooms and respective bioaccumulation prospects. The preservation of mortality among life forms is addressed in a critical cellular perspective for multitude benefits. The comprehensive cellular assessment could provide opportunity to develop strategy for therapeutic implications.

Risk assessment of cyanobacteria toxic metabolites on freshwater ecosystems applying molecular methods.

Cyanobacteria, ancient prokaryotes, interfere with ecosystem water quality through the production of cyanotoxins and bloom formation. Therefore, for water safety and public health reasons, the application of faster, sensitive, and specific tools on its risk assessment is demanded. Polymerase chain reaction (PCR) coupled with DNA sequencing can be a helpful tool for the presence and potential to cyanotoxicity. To achieve these, seven waterbodies located on the North and Center regions of Portugal were sampled for two monitoring periods (2017 and 2018). Thus, given the five risk levels proposed (none up to four cyanotoxins - mcyA, cyrC, anaC, sxtI - being detected per risk level), results showed that the great majority of the ecosystems analyzed on the presence of blooms and under climate change phenomenon (heat waves) had an elevated risk (up to four cyanotoxins being detected) corresponding to a situation of high potential of cyanotoxicity. In the opposite conditions (i.e., absence of blooms and heat waves), the risk was lowered to none or only one cyanotoxin being detected. Two ecosystems escaped this trend and demonstrated little to no alterations among risk levels from 1 year to another corresponding to a high potential of cyanotoxicity and cyanotoxins persistence in comparison to other studied ecosystems. Overall, the risk assessment undertaken suggests that other ecosystems ecological variables (physical, hydrological, or chemical) are interfering on the occurrence and persistence of cyanotoxins biosynthesis genes. Given the observed conditions (eutrophic status, bloom occurrence, and heat waves) of the analyzed ecosystems, cyanobacterial potential for toxicity seems to have increased, suggesting a need of the incorporation of other cyanotoxins apart of the regulated microcystins-LR on cyanotoxins surveillance programs of Portugal.

Surviving on low-energy light comes at a price.

Two species of photosynthetic cyanobacteria can thrive in far-red light but they either become less resilient to photodamage or less energy efficient.

Reflections on Cyanobacterial Chromatic Acclimation: Exploring the Molecular Bases of Organismal Acclimation and Motivation for Rethinking the Promotion of Equity in STEM.

Cyanobacteria are photosynthetic organisms that exhibit characteristic acclimation and developmental responses to dynamic changes in the external light environment. Photomorphogenesis is the tuning of cellular physiology, development, morphology, and metabolism in response to external light cues. The tuning of photosynthetic pigmentation, carbon fixation capacity, and cellular and filament morphologies to changes in the prevalent wavelengths and abundance of light have been investigated to understand the regulation and fitness implications of different aspects of cyanobacterial photomorphogenesis. Chromatic acclimation (CA) is the most common form of photomorphogenesis that has been explored in cyanobacteria. Multiple types of CA in cyanobacteria have been reported, and insights gained into the regulatory pathways and networks controlling some of these CA types. I examine the recent expansion of CA types that occur in nature and provide an overview of known regulatory factors involved in distinct aspects of cyanobacterial photomorphogenesis. Additionally, I explore lessons for cultivating success in scientific communities that can be drawn from a reflection on existing knowledge of and approaches to studying CA.

Rice vinasse treatment by immobilized Synechococcus pevalekii and its effect on Dunaliella salina cultivation.

The development of new strategies in microalgal studies represents an outstanding opportunity to mitigate environmental problems coupled with biomass production at a reduced cost. Here we present a combined bioprocess for the treatment of rice vinasse using immobilized cyanobacteria Synechococcus pevalekii in alginate beads followed by the use of the treated vinasse as a culture medium for Dunaliella salina biomass production. Cyanobacterial-alginate beads showed a chlorophyll a production of 0.68 × 10-3 mg bead-1 and a total carotenoid production of 0.64 × 10-3 mg bead-1. The first step showed a decrease in nitrate (91%), total solids (29%), and ions. Addition of treated vinasse into D. salina cultivation resulted in a significant increase in cell replication of about 175% (optimized cultivation). The use of natural seawater drastically reduced the medium cost to US$4.75 per m3 and the addition of treated vinasse has the potential to reduce it even more (up to 69%). This study not only provides an insight on the use of cyanobacteria for rice vinasse treatment but also demonstrates a promising lower-cost medium for marine microalgal biomass production with biotechnological purposes.

Phytotoxicity and bioconcentration of microcystins in agricultural plants: Meta-analysis and risk assessment.

Microcystins are cyanotoxins produced by many species of cyanobacteria. They are specific inhibitors of serine/threonine protein phosphatases and are phytotoxic to agricultural plants. This study used a formal meta-analysis to estimate the phytotoxicity and bioconcentration rates of agricultural plants exposed to microcystins, and the human health risk from consuming microcystin-contaminated plants. Among the 35 agricultural plants investigated, microcystins were most phytotoxic to durum wheat, corn, white mustard and garden cress. Leafy vegetables such as dill, parsley and cabbage could bioconcentrate ∼3 times more microcystins in their edible parts than other agricultural plants. Although the human health risk from ingesting microcystins could be greater for leafy vegetables than other agricultural plants, further work is needed to confirm bioconcentration of microcystins in realistic water-soil-plant environments. Still, we should avoid growing leafy vegetables, durum wheat and corn on agricultural land that is irrigated with microcystins-contaminated water and be attentive to the risk of microcystins contamination in the agricultural food supply.

Cyanobacterial Polyhydroxyalkanoates: A Sustainable Alternative in Circular Economy.

Conventional petrochemical plastics have become a serious environmental problem. Its unbridled use, especially in non-durable goods, has generated an accumulation of waste that is difficult to measure, threatening aquatic and terrestrial ecosystems. The replacement of these plastics with cleaner alternatives, such as polyhydroxyalkanoates (PHA), can only be achieved by cost reductions in the production of microbial bioplastics, in order to compete with the very low costs of fossil fuel plastics. The biggest costs are carbon sources and nutrients, which can be appeased with the use of photosynthetic organisms, such as cyanobacteria, that have a minimum requirement for nutrients, and also using agro-industrial waste, such as the livestock industry, which in turn benefits from the by-products of PHA biotechnological production, for example pigments and nutrients. Circular economy can help solve the current problems in the search for a sustainable production of bioplastic: reducing production costs, reusing waste, mitigating CO2, promoting bioremediation and making better use of cyanobacteria metabolites in different industries.

Biomarkers in bivalve mollusks and amphipods for assessment of effects linked to cyanobacteria and elodea: Mesocosm study.

The effects of cyanobacteria (Aphanizomenon flos-aquae (90%), Microcystis aeruginosa) and dense Elodea canadensis beds on the health endpoints of the amphipod Gmelinoides fasciatus and bivalve mollusc Unio pictorum were examined in mesocosms with simulated summer conditions (July-August 2018) in the environment of the Rybinsk Reservoir (Volga River Basin, Russia). Four treatments were conducted, including one control and three treatments with influencing factors, cyanobacteria and dense elodea beds (separately and combined). After 20 days of exposure, we evaluated the frequency of malformed and dead embryos in amphipods, heart rate (HR) and its recovery (HRR) after stress tests in molluscs as well as heat tolerance (critical thermal maximum or CTMax) in both amphipods and molluscs. The significant effect, such as elevated number of malformed embryos, was recorded after exposure with cyanobacteria (separately and combined with elodea) and presence of microcystins (MC) in water (0.17 µg/l, 40% of the most toxic MC-LR contribution). This study provided evidence that an elevated number (>5% of the total number per female) of malformed embryos in amphipods showed noticeable toxicity effects in the presence of cyanobacteria. The decreased oxygen under the influence of dense elodea beds led to a decrease in HR (and an increase in HRR) in molluscs. The notable effects on all studied biomarkers, embryo malformation frequency and heat tolerance in the amphipod G. fasciatus, as well as the heat tolerance and heart rate in the mollusc U. pictorum, were found when both factors (elodea and cyanobacteria) were combined. The applied endpoints could be further developed for environmental monitoring, but the obtained results support the importance of the combined use of several biomarkers and species, especially in the case of multi-factor environmental stress.

Host Genetic and Environmental Factors Shape the Composition and Function of Gut Microbiota in Populations Living at High Altitude.

The human gut microbiota is affected by genetic and environmental factors. It remains unclear how host genetic and environmental factors affect the composition and function of gut microbiota in populations living at high altitudes. We used a metagenome-wide analysis to investigate the gut microbiota composition in 15 native Tibetans and 12 Hans living on the Tibetan Plateau. The composition of gut microbiota differed significantly between these two groups (P < 0.05). The Planctomycetes was the most abundant phyla both in native Tibetans and in Hans. Furthermore, the most relatively abundant phyla for native Tibetans were Bacteroidetes (15.66%), Firmicutes (11.10%), Proteobacteria (1.32%), Actinobacteria (1.10%), and Tenericutes (0.35%), while the most relatively abundant phyla for Hans were Bacteroidetes (16.28%), Firmicutes (8.41%), Proteobacteria (2.93%), Actinobacteria (0.49%), and Cyanobacteria (0.21%). The abundance of the majority of genera was significantly higher in Tibetans than in Hans (P < 0.01). The number of microbial genes was 4.9 times higher in Tibetans than in Hans. The metabolic pathways and clusters of orthologous groups differed significantly between the two populations (P < 0.05). The abundance of carbohydrate-active enzyme modules and antibiotic resistance genes was significantly lower in Tibetans compared to Hans (P < 0.05). Our results suggest that different genetic factors (race) and environmental factors (diets and consumption of antibiotics) may play important roles in shaping the composition and function of gut microbiota in populations living at high altitudes.

Ecotoxicity assessment of microcystins from freshwater samples using a bioluminescent cyanobacterial bioassay.

The hepatotoxic cyanotoxins microcystins (MCs) are emerging contaminants naturally produced by cyanobacteria. Yet their ecological role remains unsolved, previous research suggests that MCs have allelopathic effects on competing photosynthetic microorganisms, even eliciting toxic effects on other freshwater cyanobacteria. In this context, the bioluminescent recombinant cyanobacterium Anabaena sp. PCC7120 CPB4337 (hereinafter Anabaena) was exposed to extracts of MCs. These were obtained from eight natural samples from freshwater reservoirs that contained MCs with a concentration range of 0.04-11.9 µg MCs L-1. MCs extracts included the three most common MCs variants (MC-LR, MC-RR, MC-YR) in different proportions (MC-LR: 100-0%; MC-RR: 100-0%; MC-YR: 14.2-0%). The Anabaena bioassay based on bioluminescence inhibition has been successfully used to test the toxicity of many emerging contaminants (e.g., pharmaceuticals) but never for cyanotoxins prior to this study. Exposure of Anabaena to MCs extracts induced a decrease in its bioluminescence with effective concentration decreasing bioluminescence by 50% ranging from 0.4 to 50.5 µg MC L-1 in the different samples. Bioluminescence responses suggested an interaction between MCs variants which was analyzed via the Additive Index method (AI), indicating an antagonistic effect (AI < 0) of MC-LR and MC-RR present in the samples. Additionally, MC extracts exposure triggered an increase of intracellular free Ca2+ in Anabaena. In short, this study supports the use of the Anabaena bioassay as a sensitive tool to assess the presence of MCs at environmentally relevant concentrations and opens interesting avenues regarding the interactions between MCs variants and the possible implication of Ca2+ in the mode of action of MCs towards cyanobacteria.

Cyanobacteria as an eco-friendly resource for biofuel production: A critical review.

Cyanobacteria are photosynthetic microorganisms which can be found in various environmental habitats. These photosynthetic bacteria are considered as promising feedstock for the production of the third- and the fourth-generation biofuels. The main subject of this review is highlighting the significant aspects of the biofuel production from cyanobacteria. The most recent investigations about the extraction or separation of the bio-oil from cyanobacteria are also adduced in the present review. Moreover, the genetic engineering of cyanobacteria for improving biofuel production and the impact of bioinformatics studies on the designing better-engineered strains are mentioned. The large-scale biofuel production is challenging, so the economic considerations to provide inexpensive biofuels are also cited. It seems that the future of biofuels is strongly dependent to the following items; understanding the metabolic pathways of the cyanobacterial species, progression in the construction of the engineered cyanobacteria, and inexpensive large-scale cultivation of them.

Role of cyanobacteria in agricultural and industrial sectors: an outlook on economically important byproducts.

Cyanobacteria are potential organisms, which are used as food, feed and fuel. The unique characters of cyanobacteria include short generation times, their ubiquitous presence and efficient nitrogen fixing potential. Cyanobacteria are unique organisms performing photosynthesis, bioremediation of wastewater, high biomass and biofuel productions etc. They are also used in the treatment of industrial and domestic wastewaters for the utilization or removal of ammonia, phosphates and other heavy metals (Cr, Pb, Co, Cu, Zn). Biomasses of cyanobacteria are used as biofertilizers for the improvement of nutrient or mineral status and water-holding capacity of the soil. The secondary metabolites of cyanobacteria are used in pharmaceuticals, nutraceutical and chemical industries. In the industrial sector, value-added products from cyanobacteria such as pigments, enzymes and exopolysaccharides are being produced in large scales for biomedical and health applications. Age-old applications of cyanobacteria in agroecosystems as biofertilizers (Anabaena sp; Nostoc sp.) and in industrial sectors as food products (Spirulina) have motivated the researchers to come up with much more specific applications of cyanobacteria both in agricultural and in industrial sectors. Therefore, considering the effectiveness and efficiency of cyanobacteria, the present review has enlisted the standout qualities of cyanobacteria and their potential applications in agricultural and industrial sectors for the benefit of human beings and environment.

Quantitative insights into the cyanobacterial cell economy.

Phototrophic microorganisms are promising resources for green biotechnology. Compared to heterotrophic microorganisms, however, the cellular economy of phototrophic growth is still insufficiently understood. We provide a quantitative analysis of light-limited, light-saturated, and light-inhibited growth of the cyanobacterium Synechocystis sp. PCC 6803 using a reproducible cultivation setup. We report key physiological parameters, including growth rate, cell size, and photosynthetic activity over a wide range of light intensities. Intracellular proteins were quantified to monitor proteome allocation as a function of growth rate. Among other physiological acclimations, we identify an upregulation of the translational machinery and downregulation of light harvesting components with increasing light intensity and growth rate. The resulting growth laws are discussed in the context of a coarse-grained model of phototrophic growth and available data obtained by a comprehensive literature search. Our insights into quantitative aspects of cyanobacterial acclimations to different growth rates have implications to understand and optimize photosynthetic productivity.

BioPS: System for screening and assessment of biofuel-production potential of cyanobacteria.

BACKGROUND: Cyanobacteria are one of the target groups of organisms explored for production of free fatty acids (FFAs) as biofuel precursors. Experimental evaluation of cyanobacterial potential for FFA production is costly and time consuming. Thus, computational approaches for comparing and ranking cyanobacterial strains for their potential to produce biofuel based on the characteristics of their predicted proteomes can be of great importance. RESULTS: To enable such comparison and ranking, and to assist biotechnology developers and researchers in selecting strains more likely to be successfully engineered for the FFA production, we developed the Biofuel Producer Screen (BioPS) platform (http://www.cbrc.kaust.edu.sa/biops). BioPS relies on the estimation of the predicted proteome makeup of cyanobacterial strains to produce and secrete FFAs, based on the analysis of well-studied cyanobacterial strains with known FFA production profiles. The system links results back to various external repositories such as KEGG, UniProt and GOLD, making it easier for users to explore additional related information. CONCLUSION: To our knowledge, BioPS is the first tool that screens and evaluates cyanobacterial strains for their potential to produce and secrete FFAs based on strain's predicted proteome characteristics, and rank strains based on that assessment. We believe that the availability of such a platform (comprising both a prediction tool and a repository of pre-evaluated stains) would be of interest to biofuel researchers. The BioPS system will be updated annually with information obtained from newly sequenced cyanobacterial genomes as they become available, as well as with new genes that impact FFA production or secretion.

Simple and practical on-site treatment of high microcystin levels in water using polypropylene plastic.

Microcystin (MC) is a hepatotoxin produced by various cyanobacteria during harmful algal blooms (HAB's) in freshwater environments. Advanced treatment methods can remove MC from drinking water, but are costly and do not address recreational water exposure and ecosystem health concerns. Here we investigate the feasibility of utilizing plastics as a MC-adsorbing material, for use in water resources used for recreation, agriculture, aquaculture and drinking water. Water containing 20 µg/L MC-LR was exposed to polypropylene (PP) plastic for a six-day period at varying temperatures (22, 37, 65°C). Water samples were then collected at 0, 1, 2, and 6 hour-intervals to examine short term treatment feasibility. Samples were also taken at 24 hours, 3 days, and 6 days to determine long-term treatment effectiveness. MC concentrations were analyzed using ELISA. Results showed a maximal reduction of nearly 70% of MC-LR after a 6-day treatment with PP at 65°C. Temperature enhanced MC-LR reduction over a 6-day period: 70% reduction at 65°C; 50% at 37°C; 38% at 22°C. We propose an inexpensive intervention strategy which can be deployed rapidly on-site in various source waters, including in resource-limited settings. During the high peak of HAB season, the strategy can be applied in source waters, alleviating water treatment burden for treatment plants, lowering treatment costs and reducing chemical usage.

Vertical-algal-biofilm enhanced raceway pond for cost-effective wastewater treatment and value-added products production.

A win-win strategy by the integration of wastewater treatment with value-added products production through a vertical-algal-biofilm enhanced raceway was investigated in the present study. Raceway pond was enhanced by vertically setting the biofilm in the system with a certain interval distance that could be adjusted for different light conditions and wastewater types. Two types of synthetic wastewater were treated with suitability-proven materials as biofilm carriers under four operation distances. Composition of the harvested algal biomass was analyzed. Coral velvet with 5-8 mm length villus was the optimal carrier, since it was durable and with high biomass productivity (6.95-8.11 g m-2·day-1). Nutrients in the wastewaters were efficiently removed with the COD, TN and TP reduction of over 86.61%, 73.68% and 89.85%, respectively. Wastewater with the low nutrients concentration experienced lower biomass and lipid productivity but larger biodiesel productivity and higher nutrient removal efficiency. In addition, as the operation distance increased, wastewater treatment efficiency was first increased but then decreased, while algal biomass footprint production was decreased. Differences in nutrients removal efficiencies were mainly due to the distance difference, which caused different biofilm culture surface areas and light regimes. The optimal operation distance as a function of the efficient nutrient removal and biodiesel production in this study was 6 cm.

Climate change could drive marine food web collapse through altered trophic flows and cyanobacterial proliferation.

Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems worldwide. However, most of these projections are based on ecological proxies or experiments on single species or simplified food webs. How energy fluxes are likely to change in marine food webs in response to future climates remains unclear, hampering forecasts of ecosystem functioning. Using a sophisticated mesocosm experiment, we model energy flows through a species-rich multilevel food web, with live habitats, natural abiotic variability, and the potential for intra- and intergenerational adaptation. We show experimentally that the combined stress of acidification and warming reduced energy flows from the first trophic level (primary producers and detritus) to the second (herbivores), and from the second to the third trophic level (carnivores). Warming in isolation also reduced the energy flow from herbivores to carnivores, the efficiency of energy transfer from primary producers and detritus to herbivores and detritivores, and the living biomass of detritivores, herbivores, and carnivores. Whilst warming and acidification jointly boosted primary producer biomass through an expansion of cyanobacteria, this biomass was converted to detritus rather than to biomass at higher trophic levels-i.e., production was constrained to the base of the food web. In contrast, ocean acidification affected the food web positively by enhancing trophic flow from detritus and primary producers to herbivores, and by increasing the biomass of carnivores. Our results show how future climate change can potentially weaken marine food webs through reduced energy flow to higher trophic levels and a shift towards a more detritus-based system, leading to food web simplification and altered producer-consumer dynamics, both of which have important implications for the structuring of benthic communities.