Monoraphidium Minutum Research Articles

Effect of plant growth-promoting molecules on improving biomass productivity in DISCOVR production strains

Phytohormones (Growth-Promoting Molecules, GPMs) have specific functions in the life cycle of a plant and are known to regulate plant growth, development, and stress responses independently, as well as through crosstalk with each other. These phytohormones are actively used in agriculture at scale, due to their efficiency at very low concentrations, and they also can be cost effective. Two phytohormones, auxin (indole-3-acetic acid, IAA) and gibberellic acid (GA), have also been shown to improve cell division, growth, and biomass production in algae. To test if phytohormones might have a similar beneficial result on potential algae biomass production strains, we evaluated the effect of IAA and GA3 on top-performing algae DISCOVR strains, Chlorella sorokiniana 1412, Monoraphidium minutum 26B-AM, Picochlorum celeri TG2-WT-CSM/EMRE, and Tetraselmis striata LANL1001 under laboratory conditions. Both GPMs showed growth promoting effects, but in contrast to previously published studies, we did not observe any increase in lipid accumulation with either IAA or GA3 supplementation. Then, to test phytohormone effects in a simulated outdoor environment, IAA treatments were conducted in environmental photobioreactors, revealing that IAA treatment significantly increased the growth and total biomass of M. minutum 26B-AM. In addition, investigation of the M. minutum 26B-AM genome combined with transcriptome data analysis revealed the presence of genes putatively involved in auxin biosynthesis and signaling, demonstrating that IAA pathways found in other algal species are also present in M. minutum 26B-AM. Finally, to begin to gauge whether GPM treatment is a viable approach for increasing biomass productivity in outdoor cultivation, we assessed, for the first time, the effects of adding GPMs to algae during scaled cultivation and the associated implications on economics for modeled large-scale algae farms.

A streamlined approach to characterize microalgae strains for biomass productivity under dynamic climate simulation conditions

Screening microalgae strains under static light and temperature flask conditions cannot directly quantify the biomass productivities of algae growing in the dynamically fluctuating light and temperature conditions of outdoor ponds. In this effort, we describe a testing pipeline that screens for productivity under climate simulated conditions. A validated, miniaturized Laboratory Environmental Algae Pond Simulator (mini-LEAPS) photobioreactor was used to determine optimal medium salinities and biomass productivities of cold-tolerant microalgae collected from Arctic, subarctic, Antarctic, and subalpine habitats. Strains characterized in this effort include: Chlorella antarctica UTEX1959, Chlorella sp. UTEXSNO69, Chloromonas rosae UTEXSNO11, Phaeodactylum tricornutum UTEX646, and Stichococcus minutus CCALA727. Observed productivities of the characterized strains ranged from 1.74 ± 0.25 to 8.18 ± 0.81 g m−2 day−1 (as ash-free dry weight). For each strain, a temperature tolerance profile was generated to identify the most appropriate season (s) for cultivation. The two most promising strains, Chlorella sp. UTEX SNO69 and P. tricornutum UTEX646, were tested alongside the DISCOVR winter benchmark strain Monoraphidium minutum 26B-AM in outdoor open ponds at the PNNL Algae Testbed (PAT) in Arizona. Under cold-season outdoor pond conditions, Chlorella sp. UTEXSNO69 achieved average areal biomass productivities of 8.21 ± 0.50 g m−2 day−1, not significantly different from that of the benchmark strain (8.52 ± 0.43 g m−2 day−1, p > 0.05). Under spring outdoor pond conditions, P. tricornutum UTEX646 achieved average areal biomass productivities 10.34 ± 0.27 g m−2 day−1, not significantly different from that of the benchmark (10.07 ± 0.50 g m−2 day−1) under the tested conditions (p > 0.05). The streamlined pipeline was thus demonstrated to successfully characterize productive microalgae strains for outdoor deployment by weeding out algae strains that were not productive under the tested dynamic light and temperature conditions.

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.

Outdoor annual algae productivity improvements at the pre-pilot scale through crop rotation and pond operational management strategies

The Development of Integrated Screening, Cultivar Optimization, and Verification Research (DISCOVR) collaborative consortium operated pre-pilot scale outdoor ponds to deliver much-needed multi-year, long-term and consistent, algae cultivation data relevant to understanding the current state of technology in terms of expected seasonal algae biomass productivity. Over the course of four years from 2018 to 2021, twelve identical 4.2 m2 mini-ponds were run in triplicate sets to test strains and operational strategies demonstrated in small-, indoor photobioreactors, in pursuit of increasing overall algae areal productivity and projected farm yield. Fourteen different cultivars derived from a strain screening pipeline were tested. Through deliberate seasonal crop rotation and improvements in operational strategies, annual biomass productivity increased from 11.6 to 17.6 g m−2 day−1, a > 50 % increase over the 2018 baseline. Both brackish and marine strains were included and four out of the fourteen strains consistently yielded high productivity across multiple years; brackish strains Monoraphidium minutum (26BAM) and Scenedesmus obliquus (UTEX393), and marine strains Tetraselmis striata (LANL1001) and Picochlorum celeri (TG2). These freely available datasets, which represent nearly complete annual daily coverage of cultivation metrics including weather, pond temperature and pH, nutrients, and productivity, are unique in the public domain and seek to fill agronomic and operational knowledge gaps to help in the eventual commercialization of algal biofuels and bioproducts.

DISCOVR strain screening pipeline – Part III: Strain evaluation in outdoor raceway ponds

In our previous studies, as described in the corresponding Part I and II manuscripts in this Special issue, we selected 12 promising microalgae strains from 38 strains for high biomass productivity based on their salinity preferences, temperature profiles, and biomass growth under simulated outdoor conditions. The 12 strains include 6 cold season strains (Micractium reisseri NREL14-F2, Monoraphidium minutum 26B-AM, Monoraphidium sp. MONOR1, Chlorella vulgaris LRB-AZ-1201, Tetraselmis striata LANL1001, Phaeodactylum tricornutum UTEX646) and 6 warm seasons strains (Scenedesmus obliquus DOE0152.z, Scenedesmus obliquus UTEX393, Chlorella sorokiniana DOE1116, Picochlorum renovo NREL39-A8, Picochlorum celeri TG2-WT-CSM/EMRE, Porphyridium cruentum CCMP7765). Because the preceding screening efforts were completed in indoor systems, this study focuses on quantitatively assessing these strains in outdoor raceway ponds to further eliminate those perform poorly under outdoor conditions. The trials presented in this study, categorized as either cold or warm season experiments based on water temperature, were carried out between February and June in 2018, 2019 and 2020. For each season, a benchmark strain, M. minutum 26B-AM for the cold season and S. obliquus UTEX393 for the warm season, was grown side-by-side with the new strains to provide a baseline for comparing strains cultivated under different weather conditions. The results showed that the cold season benchmark, M. minutum 26B-AM, remained the most productive cold season strain, but two new strains, P. triconutum UTEX646 and T. striata LANL1001, demonstrated robust growth in the presence of weather changes and biological contaminants. For the warm season trials, P. celeri TG2-WT-CSM/EMRE and P. cruentum CCMP675 were 39 % and 11 % more productive than the benchmark with substantially improved culture stability. Biomass compositional analyses of the strains showed that the carbohydrate, lipid (measured as fatty acid methyl esters) and protein account for 5.2–20.6 %, 7.2–11.9 %, and 21.7–53 %, of the ash-free dry matter, respectively.

DISCOVR strain pipeline screening – Part II: Winter and summer season areal productivities and biomass compositional shifts in climate-simulation photobioreactor cultures

Assessing the seasonal biomass productivity and compositional shift dynamics under simulated outdoor culture conditions of the top 21 algae strains selected during Tier I flask screening is an important step in the further prioritization of strains with regard to outdoor pond cultivation.These top 21 strains were subjected to Tier II testing in the PNNL Laboratory Environmental Algae Pond Simulator (LEAPS) photobioreactors, simulating light and temperature conditions of 20 cm deep outdoor ponds during the Arizona winter and summer season. All strains were grown in two consecutive nutrient-replete batch culture experiments at their particular optimal medium salinity to quantify their respective seasonal linear-phase areal biomass productivities. To determine biomass compositional shifts in response to nutrient-depletion, the LEAPS cultures were allowed to enter a 9-day nutrient depletion phase at the end of the second batch run. The following strains were evaluated in winter-season climate-simulated cultures and are listed in the order from highest (7.9 g m−2 day−1) to lowest (2.3 g m−2 day−1) areal N-replete biomass productivity: Monoraphidium minutum 26B-AM, Tetraselmis striata LANL1001, Chlorella vulgaris LRB AZ-1201, Micractinium reisseri NREL14-F2, Monoraphidium sp. MONOR1, Chlorella vulgaris NREL4-C12, Scenedesmus obliquus UTEX393, Scenedesmus acutus LRB-AP-0401, Nannochloropsis oceanica CCAP849/10, and Stichococcus minutus CCALA727. The following strains were evaluated in summer-season climate-simulated cultures and are listed in the order from highest (31.8 g m−2 day−1) to lowest (14.2 g m−2 day−1) areal N-replete biomass productivity: Picochlorum renovo NREL39-A8, Scenedesmus obliquus UTEX393, Porphyridium cruentum CCMP675, Picochlorum celeri TG2-WT-CSM/EMRE, Chlorella sorokiniana DOE1116, Stichococcus minor CCMP819, Picochlorum oklahomensis CCMP2329, Chlorella sorokiniana DOE1412 (UTEXB3016), Scenedesmus rubescens NREL46B-D3, Picochlorum soloecismus DOE101, Tetraselmis striata LANL1001, Scenedesmus obliquus DOE 0152.z, and Agmenellum quadruplicatum UTEX2268. All LEAPS cultures experienced a significant reduction in areal biomass productivity in response to nutrient-depletion, from 7 to 16 % in the winter season simulation and from 1 to 60 % in the summer season simulation. For 10 of the strains tested, the carbohydrate content more than doubled upon nutrient depletion, and for 9 strains, the lipid content increased by over 50 % of the initial content.

Oxygen stress mitigation for microalgal biomass productivity improvement in outdoor raceway ponds

Dissolved oxygen (DO) concentrations at supersaturated levels are commonly observed in microalgae cultures due to photosynthesis. Unlike cultivation in closed photobioreactors, the impact of excessive oxygen and the mitigation methods in open systems such as raceway ponds have hardly been studied. In this study, photosynthetic rates of Monoraphidium minutum 26B-AM and Scenedesmus obliquus UTEX393, two of the top DISCOVR strains for outdoor raceway cultivation, were compared at different DO levels. Increasing DO from 0 to 30 mg L−1 caused a 36.6 % and 26.1 % reduction in photosynthetic rate for M. minutum 26B-AM and S. obliquus UTEX393, respectively. To improve the outdoor pond biomass productivity of each strain, three oxygen stress mitigation methods were tested. The first method raised the dissolved bicarbonate concentration by an order of magnitude to favor bicarbonate transport into the cell, increasing the CO2:O2 ratio near RuBisCO, thus reducing photorespiration. Although this method increased the observed photosynthesis rate of M. minutum 26B-AM by 26 % and S. obliquus UTEX393 by 13 % in laboratory testing, it failed to improve biomass productivity under outdoor pond conditions for both strains. The second method added sodium sulfite as an oxygen scavenger to chemically lower the DO concentration in the culture. Chemical reduction of dissolved molecular oxygen did not significantly improve the biomass productivity of M. minutum 26B-AM; however, a 10 % improvement in biomass productivity for S. obliquus UTEX393 was observed. The final method sparged cultures with air to strip oxygen out of the liquid medium. This did not improve the biomass productivity of M. minutum 26B-AM, likely due to unfavorable weather conditions during cold season cultivation; however, an improvement of 36 % in biomass productivity was achieved for S. obliquus UTEX393 during the warm season cultivation. Of the three tested methods, air-sparging was the most effective and practical for improving outdoor biomass production.

Multi-omics profiling of the cold tolerant Monoraphidium minutum 26B-AM in response to abiotic stress

Microalgae that are of interest for biofuel production must be able to tolerate environmental changes that occur in outdoor cultivation systems. While algal cultures may experience daily temperature fluctuations and seasonal environmental changes, the underlying mechanisms that control and regulate physiological responses and adaptation to environmental pressures are largely unknown. Systems-level characterization enabled by functional genomics can help identify biochemical pathways that promote stability and productivity of algae in various environmental conditions. Monoraphidium minutum 26B-AM, a freshwater green microalga, was identified as a top performer in biomass production in winter season screens. We sequenced the genome of M. minutum 26B-AM and applied our multi-omics pipeline to profile this high potential strain under high salt and cold temperature perturbations. Through comparative analysis, including other green algae in the class Chlorophyceae, we identified gene families unique to the genus Monoraphidium, including a desaturase that has been linked to cold tolerance in plants. We observed that osmolytes, such as trehalose, proline and betaine, accumulate under salt stress, coinciding with upregulation of genes involved in biosynthesis of these metabolites. From the genome annotation, we reconstructed a metabolic model to provide a detailed map of the metabolic pathways and can be used to simulate growth and reaction fluxes. This multi-omics analysis provides a foundation to explore algal strain potential for biofuel applications, guides strain engineering, and expands our understanding of metabolic and regulatory mechanisms of algae in applied systems.

20 Years of Global Change on the Limnology and Plankton of a Tropical, High-Altitude Lake

The present long-term (1993–2013) study was aimed at identifying the effects of global change on the environmental characteristics and the plankton community of the tropical, high-altitude Lake Alchichica, Puebla, Mexico. We found no statistically significant increasing trend in air temperature, but an increase from 2002 to 2013, and interannual variability in the meteorological variables. Accordingly, the water temperature rose from 1993 to 2003 and remained similar until 2013. Nonetheless, on a longer-term (1966-2018), longer than the period considered in the present study, air and water temperatures showed an increasing trend in the range considered indicative of climate change. The lake displayed a characteristic warm monomictic thermal pattern but exhibited interannual variability. The planktonic community composition and structure remained similar. The small chlorophytes (e.g., Monoraphidium minutum) dominated the phytoplankton abundance, while the large diatom Cyclotella alchichicana dominated the biomass. The calanoid copepod Leptodiaptomus garciai dominated both the zooplankton abundance and biomass. However, as the temperature increased the large-size phytoplankton (i.e., C. alchichicana) abundance and biomass increased, but the small-size phytoplankton abundance and biomass, as well as the adult copepod abundance and biomass, decreased. The increase in temperature could have favoured the large-size over the small-size phytoplankton. In addition, the temperature increase could have negatively affected the calanoid copepods in two different ways—direct association with the negative effects of higher temperatures on the physiology of the copepods, or indirect association with the negative effects of higher temperatures on the small-size phytoplankton, which diminish the copepods’ food resource.

Real-time ensemble microalgae growth forecasting with data assimilation.

Accurate short-range (e.g., 7 days) microalgae growth forecasts will be beneficial for both the production and harvesting of microalgae. This study developed an operational microalgae growth forecasting system comprised of the Huesemann Algae Biomass Growth Model (BGM), the Modular Aquatic Simulation System in Two Dimensions (MASS2) hydrodynamic model, and ensemble data assimilation (DA). The novelty of this study is the use of ensemble DA to sequentially update the BGM model's initial condition (IC) with the assimilation of measured biomass optical density to improve short-range biomass forecasting skills. The forecasting system was run in pseudo-real-time and validated against observed Monoraphidium minutum 26B-AM growth in two outdoor pond cultures located in Mesa, Arizona, United States. We found the DA forecasting system could improve the 7-day microalgae forecasting skill by about 85% on average compared to model forecasts without DA. These results suggest the potential accuracy of biomass growth forecasts may be sufficient to inform real-time operational decisions, such as pond operation and harvest planning, for commercial-scale microalgae production.

Inter- and intraspecific differences in rotifer fatty acid composition during acclimation to low-quality food.

Biochemical food quality constraints affect the performance of consumers and mediate trait variation among and within consumer species. To assess inter- and intraspecific differences in fatty acid retention and conversion in freshwater rotifers, we provided four strains of two closely related rotifer species, Brachionus calyciflorus sensu stricto and Brachionus fernandoi, with food algae differing in their fatty acid composition. The rotifers grazed for 5 days on either Nannochloropsis limnetica or Monoraphidium minutum, two food algae with distinct polyunsaturated fatty acid (PUFA) profiles, before the diets were switched to PUFA-free Synechococcus elongatus, which was provided for three more days. We found between- and within-species differences in rotifer fatty acid compositions on the respective food sources and, in particular, highly specific acclimation reactions to the PUFA-free diet. The different reactions indicate inter- but also intraspecific differences in physiological traits, such as PUFA retention, allocation and bioconversion capacities, within the genus Brachionus that are most likely accompanied by differences in their nutritional demands. Our data suggest that biochemical food quality constraints act differently on traits of closely related species and of strains of a particular species and thus might be involved in shaping ecological interactions and evolutionary processes. This article is part of the theme issue 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

Spirostomum teres: A Long Term Study of an Anoxic-Hypolimnion Population Feeding upon Photosynthesizing Microorganisms

The pelagic / anoxic hypolimnion population of Spirostomum teres was investigated as a part of the long-term ciliates’ monitoring (2003–2016) in an oligo- to mesotrophic monomictic hyposaline crater lake Alchichica (Puebla / Veracruz, Mexico), including an analysis of picoplankton (both heterotrophic, HPP and autotrophic, APP) and inorganic compounds of nitrogen (ammonium, nitrite, nitrate), phosphorus (dissolved reactive phosphorus, DRP) and silicon. Additionally, detailed studies of the ciliate vertical distribution and feeding activity measured upon fluorescently labelled APP (picocyanobacteria) were carried out. The results were compared with those from a neighbour freshwater crater lake La Preciosa and with a meromictic karstic lake La Cruz (Cuenca, Spain). The ciliate vertical distribution within the water column was very well defined: During the first decade, the benthic population was frequently found throughout a developing stratification of the lake. The established stratification of the lake turned the conditions favourable for the formation of an oxycline / hypolimnion population, typically, several meters below the deep chlorophyll maximum (formed basically by diatoms); the population preferred the layers without detectable dissolved oxygen. However, an observed gradient of light (PAR) could support both oxygenic and anoxygenic photosynthesis. Late stratification after deepening of the thermocline reduced the layers with S. teres population to a minimum apparently due to the drastic change in physicochemical conditions within a metalimnion, coupled with an oxycline, and limited to 1 to 2 meters; microstratification was found. Last years, the very bottom population disappeared or it was reduced and the late stratification S. teres peaks were smaller or did not appeared. Generally, S. teres oxycline / anoxic hypolimnion population was observed from June through November. Optimum picoplankton numbers in conditions that supported the ciliate growth were found: The ciliate was peaking at APP of 0.6 to 1 × 105 cells mL–1; the optimum of HPP was observed round 1.4 × 106 cells mL–1. S. teres was efficiently feeding upon picocyanobacteria in numbers of 105 cells mL–1 reaching the clearance rate of 2000 nL cell–1h–1, which represented in average 130 to 210 cells cell–1h–1 ingested. Feeding upon purple sulphur bacteria was observed but only during the end of the lake stable stratification when the ciliate population was already dropping. On the other hand, the volume specific clearance of S. teres upon picocyanobacteria (103 h–1) did not support the hypothesis that they could serve as a sole prey. Feeding upon eukaryote phytoplankton (chlorophytes Monoraphidium minutum, diatoms Cyclotella choc tawhatcheeana) could be of higher importance that previously supposed. Additionally, a use of ingested and retained photosynthetic prokaryotes is hypothesized.

Plankton community and the relationship with the environment in saline lakes of Onon-Torey plain, Northeastern Mongolia.

The plankton community of sixteen saline lakes located on Onon-Torey plain (Northeastern Mongolia) during the filling phase and the raising of the water level was investigated in July 2011. Thirty-five taxa of phytoplankton and thirty-one species of zooplankton were found. For phytoplankton, blue-green algae (Merismopedia elegans, Anabaenopsis elenkinii, Arthrospora fusiformis, Spirulina major, Lyngbya sp., Oscillatoria sp.) and green algae (Monoraphidium minutum, Tetrastrum komarekii, Ankyra ocellata, Oocystis sp.) were dominant. For zooplankton, Filinia longiseta, Brachionus plicatilis, B. variabilis, Hexarthra mira (Rotifera), Daphnia magna, Moina brachiata, M. mongolica (Cladocera), Arctodiaptomus bacillifer, Mixodiaptomus incrassatus, Metadiaptomus asiaticus (Copepoda) dominated. Mineralization, active hydrogen ratio, dissolved oxygen and water temperature were the main factors influencing the diversity, structure and distribution of plankton organisms in the steppe lakes during low water level. The RDA analysis for phytoplankton and zooplankton from different lakes was carried out for selected two groups which included lakes and a subset related species. The first group is of oligohaline and mesohaline lakes in which mostly green algae, rotifers and copepods inhabit. The second group is of mesohaline and polyhaline lakes with mainly blue-green algae, some crustaceans and rotifers inhabiting. High abundance and biomass of Spirulina major, Oscillatoria sp. and Brachionus variabilis were observed in lakes with high mineralization, pH and temperature.

Feasibility of lipid mechanical extraction from viable Monoraphidium minutum

AbstractBackground. Mechanical stress was investigated as a mean to harvest microalgal lipids without affecting algal cells’ viability. Monoraphidium minutum was cultivated in laboratory-scale photobioreactors and suspension cultures were submitted to mechanical stress to compare a cyclone, a centrifuge and a homogenizer. Lipid content within the extracellular medium was analyzed prior to and after treatment, and the amount of released lipids was quantified. Algal cell viability was also evaluated before and after treatment.Results. After mechanical-stress treatments, 7.0 to 12.7% of the intracellular lipids of Monoraphidium minutum were released and found in the extracellular medium, while recovered algal cells presented low levels of disruption after treatments.Conclusions. To the best of our knowledge, this is the first proof-of-concept demonstration on the use of mechanical stress for lipid extraction from viable microalgae. Certain level of centrifugation proved to make algae release around 10% of their lipids to the extracellular medium. This mostly exploratory work calls for deeper investigation, paving the way for a biofuel production based on continuous lipid recovery and microalgae reuses.

Potential of Monoraphidium minutum for carbon sequestration and lipid production in response to varying growth mode

Mixotrophic growth at flask level and, autotrophic–mixotrophic and autotrophic growth in photobioreactor by utilizing CO2/air/flue gas were checked for the isolated strain of Monoraphidium minutum from polluted habitat. Our study confirmed that it is a saturated fatty acid rich (30.92–68.94%) microalga with lower degree of unsaturation oil quality (42.06–103.99) making it potential biodiesel producing candidate. It showed encouraging biomass productivity (80.3–303.8mgl−1day−1) with higher total lipid (22.80–46.54%) under optimum glucose, fructose, microalgal biodiesel waste residue and sodium acetate fed mixotrophic conditions. The pH control by intermittent CO2, continuous illumination with 30% flue gas, and utilization of biodiesel glycerin were effective schemes to ameliorate either biomass productivity or % lipids or both of these parameters at photobioreactor scale (7.5L working volume). The modulation of environmental variables (pH control, CO2 and organic substrates concentration) could augment % saturated fatty acids, such as C16:0.

Limited reversibility of bioconcentration of hydrophobic organic chemicals in phytoplankton.

Aging, reversibility, and desorption rates for the binding of hydrophobic chemicals (HOC) to phytoplankton cells have not been directly measured. Here the effect of bioconcentration time on subsequent desorption of hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs) was studied for the alga Monoraphidium minutum. Cell suspensions were exposed to HCB and PCBs spanning a range of log Kow values of 5.7 to 8.2, for 0.13 to 14 d. Subsequently, reversibility and desorption rates were assessed by extracting the chemicals from the cells using infinite sink extractions with Tenax beads or Empore disks employed in the cell suspension. Uptake was biphasic with constant relative contributions of fast surface sorption. Desorption was biphasic too and well fitted to a first order two compartment model. Increasing exposure times resulted in increasing slowly desorbing chemical fractions and decreased desorption rates from these fractions. For the most hydrophobic PCBs, slowly desorbing fractions were >80–90%, whereas desorption half-lives from these fractions ranged up to 120 days. The slow desorption rates directly prove that bioconcentration to algae can be rate limited and imply that already after a few hours of exposure, HOCs may become practically unavailable for repartitioning.

Phytoplankton chlorophyte structure as related to ENSO events in a saline lowland river (Salado River, Buenos Aires, Argentina).

We analyzed the phytoplankton present in the lower sector of the Salado River (Buenos Aires, Argentina) for 10 years (1995–2005) and detected significant changes occurring in chlorophyte abundance and species richness during La Niña event (1998–1999), which period was analyzed throughout the entire basin (main stream and tributaries). We compared the physicochemical and biologic variables between two El Niño–La Niña–Southern Oscillation (ENSO) periods – El Niño (March 1997–January 1998) and La Niña (May 1998–May 1999) – to identify possible indicators of a relationship between climatic anomalies and chlorophyte performance. Chlorophyte density increased during the La Niña. Under normal or extreme hydrologic conditions, mobile (Chlamydomonas spp.) and nonmobile (Monoraphidium spp.) chlorophytes codominated. These species belonged to Reynolds's functional groups X1 and X2, those typical of nutrient-enriched environments. Comparative analyses between El Niño and La Niña periods indicated significant differences in physicochemical (K+, dissolved polyphenols, particulate reactive phosphorus, alkalinity, pH) and biologic (species diversity and richness, phytoplankton and chlorophyte total densities) variables between the two periods at all basin sites. During the La Niña condition, species richness was greater owing to interconnected shallow lakes and drainage-channel inputs, while the Shannon diversity index was lower because of the high abundance values of Monoraphidium minutum. A detailed analysis of the chlorophytes in the entire basin, indicated that changes in density and species dominance occurred on a regional scale although diverse chlorophyte assemblages were identified in the different sectors of the Salado River basin. After La Niña event, the entire basin had the potential to revert to the previous density values, showing the resilience to global environmental changes and the ability to reestablish the general conditions of stability.

Algal diets and natural xenobiotics impact energy allocation in cladocerans. II. Moina macrocopa and Moina micrura

In freshwater lakes, changing mineral and biochemical food qualities as well as exposure to natural xenobiotics, such as humic substances (HSs) are common challenges to life history traits of zooplankters. In this contribution, we tested the bottom-up effect of different food qualities alone and in concert with exposure to increasing HS concentrations in a clone of each Moina micrura (inhabitant of Brazilian coastal lagoons) and Moina macrocopa (invasive species). Carbon, nitrogen, and phosphorus contents, fatty acid (FA) and the amino acid (AA) patterns of three coccal green algae of the summer aspect in the lagoons were analyzed. All algae were deficient in P, differed in their content of α-linolenic acid (ALA), histidine, and arginine and were lacking long-chained polyunsaturated fatty acids (PUFAs >C18). M. micrura did not grow on Desmodesmus armatus . Maximal mean lifespan and total lifespan reproduction were achieved on Pseudokirchneriella subcapitata . M. macrocopa fed all algae offered. Multiple regressions showed that ALA triggered longevity and the P-content reproduction. Exposure to HSs revealed that M. micrura reduced either its lifespan on Monoraphidium minutum or its reproduction on P. subcapitata . Conversely in M. macrocopa , lifespan on M. minutum was extended by a factor of 1.7 and offspring numbers increased by 1.4 upon HS exposure. On D. armatus an originally very low reproductive output increased maximal by a factor 4.6. Relating HS-mediated lifespan and offspring modulations of the 1.08 mM exposure to food components, it appears that ALA controls lifespan modulation even under HS stress, whereas offspring modulation seems to be controlled by C and total AA content. This indicates that, upon HS exposure, the investment of energy in body maintenance or reproduction would depend at least partly on the biochemical composition of the food available. This also shows that even short-chained dietary PUFAs may play a major role in keeping lipid peroxidation low. A comparison of the two Moina species tested revealed that M. macrocopa has the capacity to outcompete M. micrura , since it had the greater clutch size, never reduced the reproductive output upon HS-exposure, and fed all diets offered.

Comparison of cyanobacterial and green algal growth rates at different temperatures

Summary1. The hypothesis that cyanobacteria have higher optimum growth temperatures and higher growth rates at the optimum as compared to chlorophytes was tested by running a controlled experiment with eight cyanobacteria species and eight chlorophyte species at six different temperatures (20–35 °C) and by performing a literature survey.2. In the experiment, all organisms except the chlorophyte Monoraphidium minutum grew well up to 35 °C. The chlorophyte Chlamydomonas reinhardtii was the fastest‐growing organism over the entire temperature range (20–35 °C).3. Mean optimum growth temperatures were similar for cyanobacteria (29.2 °C) and chlorophytes (29.2 °C). These results are concordant with published data, yielding slightly higher mean optimum growth temperatures for cyanobacteria (27.2 °C) than for chlorophytes (26.3 °C).4. Mean growth rates of cyanobacteria at 20 °C (0.42 day−1) were significantly lower than those of chlorophytes at 20 °C (0.62 day−1). However, at all other temperatures, there were no differences between mean growth rates of cyanobacteria and chlorophytes.5. Mean growth rates at the optimum temperature were similar for cyanobacteria (0.92 day−1) and chlorophytes (0.96 day−1). However, analysis of published data revealed that growth rates of cyanobacteria (0.65 day−1) were significantly lower than those of chlorophytes (0.93 day−1) at their optimum temperatures.6. Although climate warming will probably lead to an intensification of cyanobacterial blooms, our results indicate that this might not be as a result of higher growth rates of cyanobacteria compared with their chlorophyte competitors. The competitive advantage of cyanobacteria can more likely be attributed to their ability to migrate vertically and prevent sedimentation in warmer and more strongly stratified waters and to their resistance to grazing, especially when warming reduces zooplankton body size.

Microalgae for phosphorus removal and biomass production: a six species screen for dual‐purpose organisms

AbstractMicroalgae biofuel production can be feasible when a second function is added, such as wastewater treatment. Microalgae differ in uptake of phosphorus (P) and growth, making top performer identification fundamental. The objective of this screen was to identify dual‐purpose candidates capable of high rates of P removal and growth. Three freshwater – Chlorella sp., Monoraphidium minutum sp., and Scenedesmus sp. – and three marine – Nannochloropsis sp., N. limnetica sp., and Tetraselmis suecica sp. – species were batch cultured in 250 mL flasks over 16 days to quantitate total phosphorus (TP) removal and growth as a function of P loads (control, and 5, 10, and 15 mg L−1 enrichment of control). Experimental design used 100 μmol m−2 s−1 of light, a light/dark cycle of 14/10 h, and no CO2 enrichment. Phosphorus uptake was dependent on species, duration of exposure, and treatment, with significant interaction effects. Growth was dependant on species and treatment. Not all species showed increased P removal with increasing P addition, and no species demonstrated higher growth. Nannochloropsis sp and N. limnetica sp. performed poorly across all treatments. Two dual‐purpose candidates were identified. At the 10 mg L−1 treatment Monoraphidium minutum sp. removed 67.1% (6.66 mg L−1 ± 0.60 SE) of TP at day 8, 79.3% (7.86 mg L−1 ± 0.28 SE) at day 16, and biomass accumulation of 0.63 g L−1 ± 0.06 SE at day 16. At the same treatment Tetraselmis suecica sp. removed 79.4% (6.98 mg L−1 ± 0.24 SE) TP at day 8, 83.0% (7.30 mg L−1 ± 0.60 SE) at day 16, and biomass of 0.55 g L−1 ± 0.02 SE at day 16. These species merit further study using high‐density wastewater cultures and lipid profiling to assess suitability for a nutrient removal and biomass/biofuel production scheme.