Microchloropsis Salina Research Articles

In vitro toxicity of microalgae species of the phyla chlorophyta and ochrophyta in CHO-k1 and HEP G2 cells for potential use in human nutrition

Microalgae are a promising component to enhance human nutrition, but to date only a few species have been authorized to be used in human nutrition. In this study, the in vitro toxicity of eight novel microalgae strains (Botryococcus braunii, Chlorococcum novae-angliae, Microchloropsis salina, Myrmecia bisecta, Stichococcus sp. Tetraselmis suecica, Tetradesmus obliquus and Spongiochloris minor) selected for their potential for human nutrition was investigated. N-hexane, acetone, ethanol and aqueous extracts of the lyophilized biomass were tested in the CHO-k1 and HEP G2 cell lines at concentrations of up to 1.81 mg ml-1 extracted biomass per well. None of the tested microalgae extracts reached values defined as a significant cytotoxic effect (IC50 < 0.02 mg ml-1). The highest cytotoxic effects were measured for Stichococcus sp. in both cell lines with IC50 values of 0.17 mg ml-1 for the acetone extract in CHO-k1 cell culture and 0.18 mg ml-1 for the acetone extract in HEP G2 cell culture. Most cytotoxic effects occurred with the acetone and ethanol extracts, while the water and n-hexane extracts showed almost no measurable cytotoxic effects. Only Tetraselmis suecica showed no cytotoxic effect under the chosen conditions in both tested cell lines, marking this microalgae as particularly interesting for further investigations into its use in human nutrition.

Cell Disruption and Hydrolysis of Microchloropsis salina Biomass as a Feedstock for Fermentation

Microalgae are a promising biomass source because of their capability to fixate CO2 very efficiently. In this study, the potential of Microchloropsis salina biomass as a feedstock for fermentation was explored, focusing on biomass hydrolysis by employing various mechanical and chemical cell disruption strategies in combination with enzymatic hydrolysis. Among the mechanical cell disruption methods investigated on a lab scale, namely ultrasonication, bead milling, and high-pressure homogenization, the most effective was bead milling using stainless-steel beads with a diameter of 2 mm. In this way, 87–97% of the cells were disrupted in 40 min using a mixer mill. High-pressure homogenization was also effective, achieving 86% disruption efficiency after four passes on a 30–200 L scale using biomass with 15% (w/w) solids content. Enzymatic hydrolysis of the disrupted cells using a mixture of cellulases and mannanases yielded up to 25% saccharification efficiency after 72 h. Acidic hydrolysis of undisrupted cells followed by enzymatic treatment yielded around 30% saccharification efficiency but was coupled with significant dilution of the resulting hydrolysate. Microalgal biomass hydrolysate produced was determined to have ~8.1 g L−1 sugars and 2.5% (w/w) total carbon, as well as sufficient nitrogen and phosphorus content as a fermentation medium.

Microalgal lipid production: A comparative analysis of Nannochloropsis and Microchloropsis strains

AbstractThe oleaginous genera Nannochloropsis and Microchloropsis are recognized for their lipid accumulation capacity. Microalgal lipid accumulation is triggered by nitrogen starvation, negatively affecting photosynthesis and growth. Moreover, light and temperature play pivotal roles in microalgal physiology, lipid accumulation and composition. This study focuses on comparing the responses of eight microalgal strains from Nannochloropsis (N. oceanica Necton, N. oceanica IMET1, Nannochloropsis. sp. CCAP211/78, N. oculata, and N. limnetica) and Microchloropsis (M. gaditana CCFM01, M.gaditana CCMP526, and M.salina) to light, temperature, and nitrogen availability. Biomass, lipid content and productivities were monitored under different light intensities (150 (LL) and 600 μmol photons m−2 s−1 (HL)) and temperatures (15, 25, 30℃) under nitrogen (N-) starvation and replete conditions. Under N-starvation and HL, N. sp. exhibited the highest lipid content (59%) and productivity (0.069 g L-1 day-1), while N. oculata had the lowest lipid content (37.5%) and productivity (0.037 g L-1 day-1) among the eight strains. Notably, M. gaditana CCFM01 achieved the highest EPA content (4.7%), contrasting with N.oceanica IMET1 lowest EPA content (2.9%) under 150 μmol photons m−2 s−1 and N-repletion. The response to temperature fluctuations under LL was strain-dependent. Microchloropsis salina and M. gaditana CCFM01 demonstrated the highest and lowest lipid productivities (0.069 g L-1 day-1 and 0.022 g L-1 day-1, respectively) at 15℃ under N-starvation. Moreover, significant EPA accumulation across various strains was observed in N. oculata (5.7%) under N-repletion at 15°C, surpassing M. gaditana CCFM01 by 40%. Ultimately, the physiological responses to cultivation conditions vary markedly among microalgal strains, even within the same genus or species. This knowledge is essential for selecting suitable strains for the efficient microalgal lipid production industry. Graphical Abstract Optimi zing cultivation conditions for the maximal lipid production in Nannochloropsis andMicrochloropsis

Energy-Efficient Production of Microchloropsis salina Biomass with High CO2 Fixation Yield in Open Thin-Layer Cascade Photobioreactors

Lipid production using microalgae is challenging for producing low-value-added products. Harnessing microalgae for their fast and efficient CO2 fixation capabilities may be more reasonable since algal biomass can be utilized as a precursor for various products in a biorefinery approach. This study aimed to optimize the productivity and efficiency of Microchloropsis salina biomass production in open thin-layer cascade (TLC) photobioreactors under physical simulation of suitable outdoor climate conditions, using an artificial seawater medium. Continuous operation proved to be the most suitable operating mode, allowing an average daily areal productivity of up to 27 g m−2 d−1 and CO2 fixation efficiency of up to 100%. Process transfer from 8 m2 to 50 m2 TLC photobioreactors was demonstrated, but with reduced daily areal productivity of 21 g m−2 d−1 and a reduced CO2 fixation efficiency, most probably due to increased temperatures at midday above 35 °C. An automated overnight switch-off of the circulation pumps was implemented successfully, reducing energy and freshwater requirements by ~40%. The ideal conditions for continuous production were determined to be a dilution rate of 0.150–0.225 d−1, pH of 8.5, and total alkalinity of 200–400 ppm, facilitating efficient pilot-scale production of microalgal biomass in TLC photobioreactors.

Optimization and mechanism analysis of photosynthetic EPA production in Nannochloropsis salina: Evaluating the effect of temperature and nitrogen concentrations

Microalgae, recognized as sustainable and eco-friendly photosynthetic microorganisms, play a pivotal role in converting CO2 into value-added products. Among these, Nannochloropsis salina (Microchloropsis salina) stands out, particularly for its ability to produce eicosapentaenoic acid (EPA), a crucial omega-3 fatty acid with significant health benefits such as anti-inflammatory properties and cardiovascular health promotion. This study focused on optimizing the cultivation conditions of Nannochloropsis salina to maximize EPA production. We thoroughly investigated the effects of varying temperatures and nitrogen (NaNO3) concentrations on biomass, total lipid content, and EPA proportions. We successfully identified optimal conditions at an initial NaNO3 concentration of 1.28 g.L−1 and a temperature of 21 °C. This condition was further validated by response surface methodology, which resulted in the highest EPA productivity reported in batch systems (14.4 mg.L−1.day−1). Quantitative real-time PCR and transcriptomic analysis also demonstrated a positive correlation between specific gene expressions and enhanced EPA production. Through a comprehensive lipid analysis and photosynthetic pigment analysis, we deduced that the production of EPA in Nannochloropsis salina seemed to be produced by the remodeling of chloroplast membrane lipids. These findings provide crucial insights into how temperature and nutrient availability influence fatty acid composition in N. salina, offering valuable guidance for developing strategies to improve EPA production in various microalgae species.

Photoautotrophic Production of Docosahexaenoic Acid- and Eicosapentaenoic Acid-Enriched Biomass by Co-Culturing Golden-Brown and Green Microalgae

Marine microalgae offer a sustainable alternative source for the human diet’s essential omega-3-fatty acids, including docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, none of them can produce DHA and EPA in a nutritionally balanced ratio of 1:1. As shown recently, the phototrophic co-cultivation of the golden-brown microalgae Tisochrysis lutea (DHA producer) with the green microalgae Microchloropsis salina (EPA producer) can provide microalgae biomass with a balanced DHA-to-EPA ratio with increased productivity compared to monocultures. This study evaluates whether other golden-brown (Isochrysis galbana) and green microalgae (Nannochloropsis oceanica, Microchloropsis gaditana) can enable the phototrophic batch production of omega-3 fatty acids in a nutritionally balanced ratio in co-culture. All co-cultivations applying a physically dynamic climate simulation of a repeated sunny summer day in Australia in LED-illuminated flat-plate gas lift photobioreactors resulted in increased biomass concentrations compared to their respective monocultures, achieving balanced DHA-to-EPA ratios of almost 1:1. Using urea instead of nitrate as a nitrogen source increased the EPA content by up to 80% in all co-cultures. Light spectra measurements on the light-adverted side of the photobioreactor showed that increased biomass concentrations in co-cultures could have been related to enhanced light use due to the utilization of different wavelengths of the two microalgae strains, especially with the use of green light (500–580 nm) primarily by golden-brown microalgae (I. galbana) and orange light (600–620 nm) predominantly used by green microalgae (N. oceanica). Phototrophic co-cultivation processes thus promise higher areal biomass yields if microalgae are combined with complimentary light-harvesting features.

Biocorona on Iron Oxide Nanoparticles in a Complex Biotechnological Environment: Analysis of Proteins, Lipids, and Carbohydrates

Upon their introduction into a biological environment, nanoparticles are spontaneously covered by a variety of biomolecules, forming a (multi)layer called the “biocorona”. However, the interaction of small and large molecules with nanosized materials is not fully understood and in complex aqueous systems, even less, limiting their exploitation. The objective is to gain insights into the mass partitioning between the solid and the liquid phases for the most abundant groups of biological molecules in a biotechnological milieu. Herein, the biocorona composition is analyzed after the exposure of bare iron oxide nanoparticles to Microchloropsis salina lysates to evaluate the influence of the environment's pH, temperature, and ionic strength on the adsorption of proteins, lipids, and carbohydrates. Maximum adsorption capacities reach at pH 4.0 and yield 0.47, 0.08, and 0.11 g g−1 for proteins, fatty acids, and carbohydrates, respectively. The increase in ionic strength and temperature of the environment promotes protein adsorption, the decrease in temperature raises fatty acid adsorption, and acidic pHs foster the adsorption of the three types of biomolecules. Abundance of the biomolecules plays a key role in the biocorona content. This approach should lead to further studies on complex systems to modulate the adsorption at the bio–nano interface.

From Micro to Nano: Grinding Natural Magnetite Ore for Microalgae Harvesting

Microalgae represent a promising feedstock for sustainable biomass and energy. The low cell concentration after cultivation, however, limits the current application fields. Magnetic microalgae harvesting is a recent approach to overcome the economic limitations of exploiting this natural resource. Accordingly, different particle types have been applied, mainly synthetically produced magnetic nanoparticles, though none on an industrial scale. Particle sizes between a few micrometers and a few nanometers have not been tested. We expected 200–500 nm to be advantageous for harvesting and as a compromise between the highly available surface and good separation properties. However, this intermediate magnetite particle size between the micro- and nano-scale cannot be reached via chemical synthesis. Therefore, we ground natural magnetite ore in a planetary ball mill and an agitator bead mill producing particles in the targeted size range. Applying ore particles ground from ~6 µm to 250 nm yields harvesting efficiencies comparable to synthetically produced nanoparticles (Ø ~ 10 nm), with only half the BET surface. Complete harvesting of saline microalgae Microchloropsis salina is possible with ground particles at alkaline pH. We demonstrate the feasibility of a harvesting process with natural, low-cost, easily separable, and readily available magnetite ore particles as a promising step towards exploiting valuable microalgal products in life sciences.

LED Illumination Modules Enable Automated Photoautotrophic Cultivation of Microalgae in Parallel Milliliter-Scale Stirred-Tank Bioreactors

Scalable lab-scale photobioreactors are needed for the exploration of new and improved photoautotrophic bioprocesses. Microbioreactor systems in which parallel bioreactors operate automatically are frequently employed to increase the speed of strain selection as well as the bioprocess-based exploration of heterotrophic fermentation processes. To enable the photoautotrophic operation of a commercially available parallel microbioreactor system with 48 stirred-tank bioreactors, LED illumination modules were designed to allow for individual light supply (400–700 nm) for each of the parallel bioreactors automated by a liquid handling station that performs both individual pH control and OD750 detection. The illumination modules enable dynamic variation of the incident light intensities of up to 1800 µmol m−2 s−1. Automated liquid level detection and volume control of each individual mL-scale gassed photobioreactor has to be established to compensate for evaporation because of the long process times of several days up to weeks. Photoautotrophic batch processes with Microchloropsis salina that employ either varying constant incident light intensities or day and night dynamics resulted in a standard deviation of OD750 of up to a maximum of 10%, with the exception of high-photoinhibiting incident light intensities. The established photoautotrophic microbioreactor system enables the automated investigation of microalgae processes in up to 48 parallel stirred photobioreactors and is thus a new tool that enables efficient characterization and development of photoautotrophic processes with microalgae.

Storage and Algal Association of Bacteria That Protect Microchloropsis salina from Grazing by Brachionus plicatilis.

Loss of algal production from the crashes of algal mass cultivation systems represents a significant barrier to the economic production of microalgal-based biofuels. Current strategies for crash prevention can be too costly to apply broadly as prophylaxis. Bacteria are ubiquitous in microalgal mass production cultures, however few studies investigate their role and possible significance in this particular environment. Previously, we demonstrated the success of selected protective bacterial communities to save Microchloropsis salina cultures from grazing by the rotifer Brachionus plicatilis. In the current study, these protective bacterial communities were further characterized by fractionation into rotifer-associated, algal-associated, and free-floating bacterial fractions. Small subunit ribosomal RNA amplicon sequencing was used to identify the bacterial genera present in each of the fractions. Here, we show that Marinobacter, Ruegeria, and Boseongicola in algae and rotifer fractions from rotifer-infected cultures likely play key roles in protecting algae from rotifers. Several other identified taxa likely play lesser roles in protective capability. The identification of bacterial community members demonstrating protective qualities will allow for the rational design of microbial communities grown in stable co-cultures with algal production strains in mass cultivation systems. Such a system would reduce the frequency of culture crashes and represent an essentially zero-cost form of algal crop protection.

DISCOVR strain pipeline screening – Part I: Maximum specific growth rate as a function of temperature and salinity for 38 candidate microalgae for biofuels production

To identify high productivity strains for microalgal biofuels generation, the maximum specific growth rate of 38 strains was measured as a function of salinity (i.e., 5, 15, and 35 PSU) and temperature (i.e., at 8 temperatures along a linear gradient from ca. 5 to 45 °C) to determine the most suitable growth medium salinity and best growing season, respectively, for outdoor raceway pond cultivation. The following strains were evaluated: Agmenellum quadruplicatum UTEX 2268, Anabaena sp. ATCC 33081, Arthrospira fusiformis UTEX 2721, Arthrospira platensis UTEX 3086, Chlorella vulgaris NREL 4-C12, Chlorella autotrophica CCMP 243, Chlorella sorokiniana DOE1044, Chlorella sorokiniana DOE 1116, Chlorella sorokiniana DOE 1412 (UTEXB3016), Chlorella vulgaris LRB AZ-1201, Chlorococcum littorale UTEX 117, Chlorococcum sp. UTEX-B P7, Chloromonas reticulata CCALA 870, Coelastrella sp. DOE 0202, Cyanobacterium sp. AB1, Micractinium reisseri NREL 14-F2, Microchloropsis gaditana CCMP1894, Microchloropsis salina CCMP 1776, Monoraphidium sp. MONOR1, Monoraphidium minutum 26B-AM, Nannochloropsis oceanica CCAP 849/10, Oscillatoria cf. priestleyi CCMEE 5020.1-1, Picochlorum celeri TG2-WT-CSM/EMRE, Picochlorum oklahomensis CCMP 2329, Picochlorum renovo NREL 39-A8, Picochlorum soloecismus DOE 101, Porphyridium cruentum CCMP 675, Scenedesmus acutus LRB-AP-0401, Scenedesmus obliquus DOE 0152.z, Scenedesmus obliquus UTEX393,Scenedesmus rubescens NREL 46B-D3, Scenedesmus sp. IITRIND2, Stichococcus minor CCMP 819, Stichococcus minutus CCALA 727, Synechococcus elongatus UTEX2973.1, Tetraselmis striata LANL 1001, Tisochrysis lutea CCMP 1324, and Tribonema minus UTEXB3156. For each strain, the identity and the presence of bacterial cohorts was determined using 18S and 16S rDNA sequencing, respectively. The maximum specific growth rate versus temperature data were also used to determine the activation energies (Arrhenius equation) for most strains. For all strains, the measured salinity and temperature tolerance data were compared to those reported in the literature. The fastest growing strains were down-selected for subsequent biomass productivity measurements in climate-simulation photobioreactors, as reported in the next paper in the issue.

Simultaneous photoautotrophic production of DHA and EPA by Tisochrysis lutea and Microchloropsis salina in co-culture

Marine microalgae have received much attention as a sustainable source of the two health beneficial omega-3-fatty acids docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, photoautotrophic monocultures of microalgae can only produce either DHA or EPA enriched biomass. An alternative may be the photoautotrophic co-cultivation of Tisochrysis lutea as DHA-producer with Microchloropsis salina for simultaneous EPA production to obtain EPA- and DHA-rich microalgae biomass in a nutritionally balanced ratio. Photoautotrophic co-cultivation processes of T. lutea and M. salina were studied, applying scalable and fully controlled lab-scale gas-lift flat-plate photobioreactors with LED illumination for dynamic climate simulation of a repeated sunny summer day in Australia [day–night cycles of incident light (PAR) and temperature]. Monocultures of both marine microalgae were used as reference batch processes. Differences in the autofluorescence of both microalgae enabled the individual measurement, of cell distributions in co-culture, by flow cytometry. The co-cultivation of T. lutea and M. salina in artificial sea water with an inoculation ratio of 1:3 resulted in a balanced biomass production of both microalgae simultaneously with a DHA:EPA ratio of almost 1:1 (26 mgDHA gCDW−1, and 23 mgEPA gCDW−1, respectively) at harvest after depletion of the initially added fertilizer. Surprisingly, more microalgae biomass was produced within 8 days in co-cultivation with an increase in the cell dry weight (CDW) concentration by 31%, compared to the monocultures with the same amount of light and fertilizer. What is more, DHA-content of the microalgae biomass was enhanced by 33% in the co-culture, whereas EPA-content remained unchanged compared to the monocultures.Graphical

A Modeled High-Density Fed-Batch Culture Improves Biomass Growth and β-Glucans Accumulation in Microchloropsis salina.

Algae and microalgae are used as a source of different biomolecules, such as lipids and carbohydrates. Among carbohydrates, polysaccharides, such as β-glucans, are important for their application as antioxidants, antisepsis, and immunomodulators. In the present work, the β-glucans production potential of Microchloropsis salina was assessed using two different culture conditions: a high-density batch and a modeled high-density fed-batch. From the biochemical parameters determined from these two cultures conditions, it was possible to establish that the modeled high-density fed-batch culture improves the biomass growth. It was possible to obtain a biomass productivity equal to 8.00 × 10-2 ± 2.00 × 10-3 g/(L × day), while the batch condition reached 5.13 × 10-2 ± 4.00 × 10-4 g/(L × day). The same phenomenon was observed when analyzing the β-glucans accumulation, reaching volumetric productivity equal to 5.96 × 10-3 ± 2.00 × 10-4 g of product/(L × day) against the 4.10 × 10-3 ± 2.00 × 10-4 g of product/(L × day) obtained in batch conditions. These data establish a baseline condition to optimize and significantly increase β-glucan productivity, as well as biomass, adding a new and productive source of this polymer, and integrating its use in potential applications in the human and animal nutraceutical industry.

Influence of nutrient supplementation and stress conditions on the biomass and lipid production of Microchloropsis salina for biodiesel production

This work aimed to introduce a new technique for improving sustainable biodiesel from Microchloropsis salina by examining the impact of various nitrogen sources, salt stress, and carbon enrichment, individually or in combination, to determine the best treatment conditions for biomass and lipid productivity as well as biodiesel quality. M. salina effectively utilizes nitrate (NaNO3 and KNO3) and organic nitrogen (especially yeast extract and glycine) but not ammonium for growth. The highest biomass and lipid productivity were observed on yeast extract (0.11 g L−1 day−1 and 52.11 μgmL−1 day−1, respectively). Lipid production enhanced by 80% under 300 mM of NaCl, while growth increased only by 30%. Acetate could not be used to cultivate the alga mixotrophically; only glucose and glycerol were effective. The ideal organic carbon supply values for glucose and glycerol were 3 g L−1 and 2 g L−1, respectively. Nutrition by 2 g L−1 glycerol promoted biomass and lipid productivities by 62% and 95%, respectively, while biomass productivity was reduced by 16% under combined and lipid productivity increased by 80%. All treatments significantly improved the biomass and biodiesel quality-related fatty acid profile.

Bacterial Community Assembly, Succession, and Metabolic Function during Outdoor Cultivation of Microchloropsis salina.

Outdoor cultivation of microalgae has promising potential for renewable bioenergy, but there is a knowledge gap on the structure and function of the algal microbiome that coinhabits these ecosystems. Here, we describe the assembly mechanisms, taxonomic structure, and metabolic potential of bacteria associated with Microchloropsis salina cultivated outdoors. Open mesocosms were inoculated with algal cultures that were either free of bacteria or coincubated with one of two different strains of alga-associated bacteria and were sampled across five time points taken over multiple harvesting rounds of a 40-day experiment. Using quantitative analyses of metagenome-assembled genomes (MAGs), we tracked bacterial community compositional abundance and taxon-specific functional capacity involved in algal-bacterial interactions. One of the inoculated bacteria (Alteromonas sp.) persisted and dispersed across mesocosms, whereas the other inoculated strain (Phaeobacter gallaeciensis) disappeared by day 17 while a taxonomically similar but functionally distinct Phaeobacter strain became established. The inoculated strains were less abundant than 6 numerically dominant newly recruited taxa with functional capacities for mutualistic or saprophytic lifestyles, suggesting a generalist approach to persistence. This includes a highly abundant unclassified Rhodobacteraceae species that fluctuated between 25% and 77% of the total community. Overall, we did not find evidence for priority effects exerted by the distinct inoculum conditions; all mesocosms converged with similar microbial community compositions by the end of the experiment. Instead, we infer that the 15 total populations were retained due to host selection, as they showed high metabolic potential for algal-bacterial interactions such as recycling alga-produced carbon and nitrogen and production of vitamins and secondary metabolites associated with algal growth and senescence, including B vitamins, tropodithietic acid, and roseobacticides. IMPORTANCE Bacteria proliferate in nutrient-rich aquatic environments, including engineered algal biofuel systems, where they remineralize photosynthates, exchange secondary metabolites with algae, and can influence system output of biomass or oil. Despite this, knowledge on the microbial ecology of algal cultivation systems is lacking, and the subject is worthy of investigation. Here, we used metagenomics to characterize the metabolic capacities of the predominant bacteria associated with the biofuel-relevant microalga Microchloropsis salina and to predict testable metabolic interactions between algae and manipulated communities of bacteria. We identified a previously undescribed and uncultivated organism that dominated the community. Collectively, the microbial community may interact with the alga in cultivation via exchange of secondary metabolites which could affect algal success, which we demonstrate as a possible outcome from controlled experiments with metabolically analogous isolates. These findings address the scalability of lab-based algal-bacterial interactions through to cultivation systems and more broadly provide a framework for empirical testing of genome-based metabolic predictions.

Identification of Effector Metabolites Using Exometabolite Profiling of Diverse Microalgae.

ABSTRACTDissolved exometabolites mediate algal interactions in aquatic ecosystems, but microalgal exometabolomes remain understudied. We conducted an untargeted metabolomic analysis of nonpolar exometabolites exuded from four phylogenetically and ecologically diverse eukaryotic microalgal strains grown in the laboratory, freshwater Chlamydomonas reinhardtii, brackish Desmodesmus sp., marine Phaeodactylum tricornutum, and marine Microchloropsis salina, to identify released metabolites based on relative enrichment in the exometabolomes compared to cell pellet metabolomes. Exudates from the different taxa were distinct, but we did not observe clear phylogenetic patterns. We used feature-based molecular networking to explore the identities of these metabolites, revealing several distinct di- and tripeptides secreted by each of the algae, lumichrome, a compound that is known to be involved in plant growth and bacterial quorum sensing, and novel prostaglandin-like compounds. We further investigated the impacts of exogenous additions of eight compounds selected based on exometabolome enrichment on algal growth. Of these compounds, five (lumichrome, 5′-S-methyl-5′-thioadenosine, 17-phenyl trinor prostaglandin A2, dodecanedioic acid, and aleuritic acid) impacted growth in at least one of the algal cultures. Two of these compounds (dodecanedioic acid and aleuritic acid) produced contrasting results, increasing growth in some algae and decreasing growth in others. Together, our results reveal new groups of microalgal exometabolites, some of which could alter algal growth when provided exogenously, suggesting potential roles in allelopathy and algal interactions.IMPORTANCE Microalgae are responsible for nearly half of primary production on earth and play an important role in global biogeochemical cycling as well as in a range of industrial applications. Algal exometabolites are important mediators of algal-algal and algal-bacterial interactions that ultimately affect algal growth and physiology. In this study, we characterize exometabolomes across marine and freshwater algae to gain insights into the diverse metabolites they release into their environments (“exudates”). We observe that while phylogeny can play a role in exometabolome content, environmental conditions or habitat origin (freshwater versus marine) are also important. We also find that several of these compounds can influence algal growth (as measured by chlorophyll production) when provided exogenously, highlighting the importance of characterization of these novel compounds and their role in microalgal ecophysiology.

Natural magnetite ore as a harvesting agent for saline microalgae Microchloropsis salina

Inefficient cell separation is considered to be a critical bottleneck when exploiting microalgal biomass as a renewable resource. Since cell density after cultivation is usually <5% (bio dried mass), new methods for concentrating biomass are being developed, and magnetic separation is a recent approach. In this study, we characterize magnetic microparticles (MMPs) derived from natural iron ores and utilize them to harvest saline microalgae Microchloropsis salina (previously Nannochloropsis salina). A harvesting efficiency for M. salina of up to 98% was reached at alkaline conditions, via magnetic separation. The precipitation of medium components (mainly calcium phosphate and magnesium hydroxide) induced flocculation of the algal cells around the MMPs at an alkaline pH. Our results demonstrate the feasibility of an MMP-mediated harvesting process for saline microalgae as a promising first step towards the separation and fractionation of valuable microalgal products for applications in various life science fields.

Janthinobacter additions reduce rotifer grazing of microalga Microchloropsis salina in biotically complex communities

Grazing and parasitism in algal production systems are significant causes of crop loss. Biological control of algal ponds, such as application of protective bacteria, represents a promising alternative to current mitigation strategies. The major barriers to probiotic methods are the lack of identified protective bacteria and uncertainty of scale-up effects, including potential negative interactions with the resident algal microbiome. Here, we report that application of Janthinobacter lividum affords robust protection against rotifer (Brachionus plicatilis) grazing on Microchloropsis salina. Protection was observed at laboratory scale from live bacteria and solvent extract additions as well as in biologically complex communities from bacterial additions to outdoor mesocosms. J. lividum persisted in outdoor communities for at least 3 days following addition, and did not lead to selective exclusion of specific taxa in the resident microbiome. These results demonstrate that J. lividum can provide protection against grazers in these diverse communities, without severe effects on the resident microbiome. Our results suggest that J. lividum is a promising treatment to mitigate algal crop losses due to pests. Additionally, the study highlights the importance of an ecologically-informed approach to algal crop management that will aid future applications in the biological control of algal ponds.

Continuous Production of Lipids with Microchloropsis salina in Open Thin-Layer Cascade Photobioreactors on a Pilot Scale

Studies on microalgal lipid production as a sustainable feedstock for biofuels and chemicals are scarce, particularly those on applying open thin-layer cascade (TLC) photobioreactors under dynamic diurnal conditions. Continuous lipid production with Microchloropsis salina was studied in scalable TLC photobioreactors at 50 m2 pilot scale, applying a physically simulated Mediterranean summer climate. A cascade of two serially connected TLC reactors was applied, promoting biomass growth under nutrient-replete conditions in the first reactor, while inducing the accumulation of lipids via nitrogen limitation in the second reactor. Up to 4.1 g L−1 of lipids were continuously produced at productivities of up to 0.27 g L−1 d−1 (1.8 g m2 d−1) at a mean hydraulic residence time of 2.5 d in the first reactor and 20 d in the second reactor. Coupling mass balances with the kinetics of microalgal growth and lipid formation enabled the simulation of phototrophic process performances of M. salina in TLC reactors in batch and continuous operation at the climate conditions studied. This study demonstrates the scalability of continuous microalgal lipid production in TLC reactors with M. salina and provides a TLC reactor model for the realistic simulation of microalgae lipid production processes after re-identification of the model parameters if other microalgae and/or varying climate conditions are applied.

Light reflection spectra as a tool for direct and real-time determination of biomass and pigments in the microalgae Microchloropsis salina

To meet the increasing demand for mass-produced microalgae, production processes must be optimised and monitored. The herein described optical sensors provide an instantaneous and direct opportunity to monitor biological and biochemical information for microalgae cultivation. Combination of expertise in natural science and engineering, as well as the application of novel data acquisition and analysis methods, are required to develop an appropriate system for industrial purpose. Prior to this, the correlation between biological and physical parameters must be determined. In this work, we combined colour science with the experimentally determined dataset from the cultivation of Microchloropsis salina. Our results indicate a resilient correlation between algal biomass and its specific pigment concentration with the determined reflection spectrum. Data evaluation allowed us to establish identification models for contactless quantification of the respective biological parameter in large-scale automated bioreactors.