Μmol Photons Research Articles

Two-stage lipid induction in the microalga Tetraselmis striata CTP4 upon exposure to different abiotic stresses

Tetraselmis striata CTP4 is a euryhaline, robust, fast-growing microalga suitable for wastewater treatment and industrial production. Lipid production was induced through a two-stage cultivation strategy: a 1st stage under standard growth-promoting conditions (100 μmol photons m−2 s−1, salinity 36 ppt and 20 °C) to achieve high biomass concentration and a 2nd stage of 6 days for lipid induction by the application of abiotic stresses such as nutrient depletion, high light intensity (200 and 400 μmol photons m−2 s−1), high salinity (75 and 100 ppt), and extreme temperatures (5 and 35 °C). Although nutrient depletion always resulted in a decrease in biomass productivity, it had also the highest impact on lipid induction. The highest lipid content (43.2%) and lipid productivity (29.2 mg L−1 d−1) were obtained using a combination of nutrient depletion and high light intensity (400 μmol m−2 s−1). The fatty acid profile was mainly composed of C16:0 (palmitic), C18:1 (oleic) and C18:2 (linoleic) acids. The low content of unsaturated fatty acids and absence of C18:3 (linolenic) acid render the oil of this microalga suitable for biodiesel production, a renewable source of energy.

Modulation of VOC fingerprint and alteration of physiological responses after supplemental LED light in green- and red-leafed sweet basil (Ocimum basilicum L.)

Narrowband green (G), blue (B), red (R), and polychromatic (W ‒ R:G:B, 1:1:1) lights were supplemented (250 µmol photon m‒2 s‒1; 5 h d−1; 21 d) to ambient light with Light Emitting Diodes (LED) in green- (‘Tigullio’; TI) and red-leafed (‘Red Rubin’; RR) sweet basil (Ocimum basilicum L.) plants. The aim of this work was to evaluate LED-triggered variations in biometric and morpho-anatomical traits, photosynthesis and secondary metabolite production to ‘photomodulate’ plant performance via monochromatic LED light supplementation.In both the cultivars, light supplementation did not alter plant biomass production compared to controls and at the amplitude applied therein any LED supplementation resulted in oxidative stress, as evidenced by slight changes in chlorophyll fluorescence parameters and H2O2 staining in leaves. Conversely, monochromatic LEDs selectively modulate metabolomics profile in both green- and red-leafed basil; e.g., B lights increased polyphenol content in TI, whilst G light resulted effective in reducing cyanidin-3-coumaroil-glucoside one of the prevalent acylated anthocyanin of RR. Volatilome profile unveiled profound waveband-dependent alterations though consistently eugenol, characterised by a clove flavor, and also considered one of the major toxic compounds in sweet basil, decreased with all the LED treatments, making green-leafed basil a more pleasant and safer product.Our dataset offers the clear evidence that monochromatic LED light supplementation represents a valid tool to modulate the accumulation of targeted secondary metabolites in planta.

Photoinhibition of the Picophytoplankter Synechococcus Is Exacerbated by Ocean Acidification

The marine picocyanobacterium Synechococcus accounts for a major fraction of the primary production across the global oceans. However, knowledge of the responses of Synechococcus to changing pCO2 and light levels has been scarcely documented. Hence, we grew Synechococcus sp. CB0101 at two CO2 concentrations (ambient CO2 AC:410 μatm; high CO2 HC:1000 μatm) under various light levels between 25 and 800 μmol photons m−2 s−1 for 10–20 generations and found that the growth of Synechococcus strain CB0101 is strongly influenced by light intensity, peaking at 250 μmol m−2 s−1 and thereafter declined at higher light levels. Synechococcus cells showed a range of acclimation in their photophysiological characteristics, including changes in pigment content, optical absorption cross section, and light harvesting efficiency. Elevated pCO2 inhibited the growth of cells at light intensities close to or greater than saturation, with inhibition being greater under high light. Elevated pCO2 also reduced photosynthetic carbon fixation rates under high light but had smaller effects on the decrease in quantum yield and maximum relative electron transport rates observed under increasing light intensity. At the same time, the elevated pCO2 significantly decreased particulate organic carbon (POC) and particulate organic nitrogen (PON), particularly under low light. Ocean acidification, by increasing the inhibitory effects of high light, may affect the growth and competitiveness of Synechococcus in surface waters in the future scenario.

Growth and yield of Syagrus schizophylla (Mart.) Glass. in response to light gradients

This research studied growth and yield of Syagrus schizophylla, an extinction-endangered ornamental palm, grown under five light gradients. The treatments were: G1 - PAR=1234.10 μmol photons m-2 s-1, G2 - PAR=913.16 μmol photons m-2 s-1, G3 - PAR=666.34 μmol photons m-2 s-1, G4 - PAR=419.56 μmol photons m-2 s-1 and G5 - PAR=534.77 μmol photons m-2s-1. Before the experiment and at three, five and seven months of treatment, growth (plant height, collar diameter, number of leaves, petiole length, leaf length and width), gas exchange, chlorophyll a, and leaf green color intensity were assessed. The highest net photosynthetic rates were observed in plants under G2, G3 and G4. Values of maximum quantum efficiency (Fv/Fm) over 0.75 were observed under G2. At seven months, estimated SPAD values were 36 in G2 plants and 32 in G1 plants. According to the Dickson quality index (DQI), presented the highest growth and development rates. We conclude that G2 suits plants to be transplanted into the field, whereas G3 would be best for plants grown under shade environments. Highlights: Syagrus schizophylla is an extinction endangered ornamental palm. One layer of Red Chromatinet® 50% should be recommended for the first year of growth of schizophylla plants to be later transplanted to the field. Two Red Chromatinet® 50% layers would be best for plants meant to grow under shade environments. The highest net photosynthetic rates were observed in plants under G2, G3 and G4.

SYNERGISTIC EFFECTS OF NITROGEN DEPRIVATION AND HIGH IRRADIANCE TO ENHANCE BIOMASS AND LIPID PRODUCTION IN NANNOCHLOROPSIS

Nannochloropsis, due to its high lipid content, small size and growth rate, can be exploited for the production of biofuel and other value-added products. This study analyzed synergistic responses of high irradiance and nitrogen deprivation on Nannochloropsis cells to enhance biomass and lipid production. The growth of Nannochloropsis was first optimized under different irradiance 50, 100, 150, 200 and 250 μmol photons m-2 s-1. The maximum specific growth rate (0.25 day-1) and dry weight (0.67 g L-1) were obtained (p<0.05) at photosynthetically active radiation (PAR) of 200 µmol photons m-2 s-1, further increase in light intensity decreased the growth rate and dry weight up to 0.2 day-1 and 0.41g L-1, respectively. The stress of high light for a short period increased the lipid content by 51.1% and decreased the protein content by 35.2% over the control values. In the second phase of the study, the combined stress of high light intensity of 200 µmol photons m-2 s-1 PAR and nitrate depletion (50%, 75%, 100% N-) were studied and observed significant (p<0.05) increase in lipid content from 21.3±1.4% to 43.2±1.56% DCW and decrease in protein from 30.7±1.3% to 16.3±1.2% DCW, respectively. The highest lipid productivity (140 mg L-1 d-1) had been observed in a culture grown at 75% N- starved cells (p<0.05). However, the further increase of nitrate deprivation to 100% decreased the lipid productivity to 107 mg L-1 d-1. Maximum accumulations of TG (19.6% DCW) were observed on 6 days (early stationary phase) in a 100% nitrogen deprived medium, although significant accumulation was observed on 4 days and 6 days of nitrate reduction.

Transcriptome analysis of two bloom-forming Prorocentrum species reveals physiological changes related to light and temperature

Temperature and light substantially influence red tide succession. However, it remains unclear whether the molecular mechanisms differ among species. In this study, we measured the variation in the physiological parameters of growth and pigments and transcriptional levels of two bloom-forming dinoflagellates, namely Prorocentrum micans and P. cordatum. This was undertaken in four treatments that represented two factorial temperature combinations (LT: 20 °C, HT: 28 °C) and light conditions (LL: 50 µmol photons m-2 s-1, HL: 400 µmol photons m-2 s-1) for 7-day batch culture. Growth under high temperature and high light (HTHL) was the fastest, while growth under high temperature and low light (HTLL) was the slowest. The pigments (chlorophyll a and carotenoids) decreased significantly in all high light (HL) treatments, but not in high temperature (HT) treatments. HL alleviated the low light-caused photolimitation and enhanced the growth of both species at low temperatures. However, HT inhibited the growth of both species by inducing oxidative stress under low light conditions. HL mitigated the HT-induced stress on growth in both species by upregulating photosynthesis, antioxidase activity, protein folding, and degradation. The cells of P. micans were more sensitive to HT and HL than those of P. cordatum. This study deepens our understanding of the species-specific mechanism of dinoflagellates at the transcriptomic level, adapting to the future ocean changes including higher solar radiation and higher temperatures in the upper mixed layer.

Effects of global change on the ability of stream biofilm to dissipate the herbicide glyphosate

The herbicide glyphosate is contaminating a large number of freshwater ecosystems worldwide and its fate and effects remains uncertain in light of the effects of global change. The present study examines how variations in water temperature and light availability relative to global change affect the ability of stream biofilms to degrade the herbicide glyphosate. Biofilms were exposed in microcosms to two levels of water temperature simulating global warming (Ambient = 19–22 °C and Warm = 21–24 °C) and three levels of light representative of riparian habitat destruction due to land use change (Dark = 0, Intermediate = 600, High = 1200 μmol photons m−2 s−1). Biofilms were acclimated to six different experimental treatments, namely i) ambient temperature without light (AMB_D), ii) ambient temperature and intermediate light (AMB_IL), iii) ambient temperature and high light (AMB_HL), iv) warm temperature without light (WARM_D), v) warm temperature and intermediate light (WARM_IL) and vi) warm temperature and high light (WARM_HL). The ability of biofilms to degrade 50 μg L−1 of glyphosate was tested. Results showed that water temperature increase, but not light availability increase, significantly increased aminomethyl phosphonic acid (AMPA) production by biofilms. However, the combined increase of temperature and light generated the shortest time to dissipate half of the glyphosate supplied and/or half of the maximum AMPA produced (6.4 and 5.4 days, respectively) by biofilms. Despite light had a major effect in modulating biofilm structural and functional descriptors, the response of certain descriptors (i. e. chlorophyll-a concentration, bacterial density and diversity, nutrient content and PHO activity) to light availability increase depended on water temperature. Specifically, the biofilms in the WARM_HL treatment displayed the highest Glucosidase: Peptidase and Glucosidase: Phosphatase enzyme activity ratios and the lowest biomass C: N molar ratios compared to the other treatments. According to these results, warmer temperatures and high light availability could have been exacerbating the decomposition of organic C compounds in biofilms, including the use of glyphosate as a C source for microbial heterotrophs. This study shows that ecoenzymatic stoichiometry and xenobiotic biodegradation approaches can be combined to better understand the functioning of biofilms in pesticide-polluted streams.

Variation in Photosynthetic Efficiency under Fluctuating Light between Rose Cultivars and its Potential for Improving Dynamic Photosynthesis

Photosynthetic efficiency under both steady-state and fluctuating light can significantly affect plant growth under naturally fluctuating light conditions. However, the difference in photosynthetic performance between different rose genotypes is little known. This study compared the photosynthetic performance under steady-state and fluctuating light in two modern rose cultivars (Rose hybrida), "Orange Reeva" and "Gelato", and an old Chinese rose plant Rosa chinensis cultivar, "Slater's crimson China". The light and CO2 response curves indicated that they showed similar photosynthetic capacity under steady state. The light-saturated steady-state photosynthesis in these three rose genotypes was mainly limited by biochemistry (60%) rather than diffusional conductance. Under fluctuating light conditions (alternated between 100 and 1500 μmol photons m-2 m-1 every 5 min), stomatal conductance gradually decreased in these three rose genotypes, while mesophyll conductance (gm) was maintained stable in Orange Reeva and Gelato but decreased by 23% in R. chinensis, resulting in a stronger loss of CO2 assimilation under high-light phases in R. chinensis (25%) than in Orange Reeva and Gelato (13%). As a result, the variation in photosynthetic efficiency under fluctuating light among rose cultivars was tightly related to gm. These results highlight the importance of gm in dynamic photosynthesis and provide new traits for improving photosynthetic efficiency in rose cultivars.

Effect of light-mediated variations of colony morphology on the buoyancy regulation of Microcystis colonies

Light is an important driver of algal growth and for the formation of surface blooms. Long-term buoyancy maintenance of Microcystis colonies is crucial for their aggregation at the water surface and the following algal bloom development. However, the effect of light-mediated variations of colony morphology on the buoyancy regulation of Microcystis colonies remains unclear. In this study, growth parameters, colony morphology and floatation/sinking performance of Microcystis colonies were determined to explore how variations in colony morphology influence the buoyancy of colonies under different light conditions. We quantified colony compactness through the cell volume to colony volume ratio (VR) and found different responses of colony size and VR under different light intensities. Microcystis colonies with higher VR could stay longer at the water surface under low light conditions, which was beneficial for the long-term growth and buoyancy maintenance. However, increased colony size and decreased compactness were observed at a later growth stage under relatively higher light intensity (i.e., >108 µmol photons m−2 s−1). Interestingly, we found a counterintuitive negative correlation between colony size and buoyancy of Microcystis under high light intensity. Additionally, we found that the influence of colony morphology on buoyancy was stronger at high light intensity. These results indicate that light could regulate the buoyancy via colonial morphology and that the role of colony morphology in buoyancy regulation needs to be accounted for in further studies under variable environmental conditions.

The influence of light on the availability of photoreactive and photostable iron(III)–ligand complexes to diatoms

AbstractUptake of iron (Fe) by eukaryotic phytoplankton is suggested to proceed by a reductive pathway in which Fe(III) bound to inorganic and organic ligands is reduced prior to Fe internalization. Photochemical reduction of the Fe–ligand complexes can increase Fe bioavailability, but the role of light in regulating physiological processes related to Fe acquisition is not well known. Here, we report how model Fe–ligand complexes differing in photolability affected growth, cellular Fe reduction, and Fe uptake rates of two marine diatoms as a function of irradiance. Growth rates of Thalassiosira oceanica and Phaeodactylum tricornutum in media amended with Fe complexed with ethylenediaminetetraacetic acid (Fe‐EDTA) and desferrioxamine B (FeDFB) increased linearly with light between 50 and 400 μmol photons m−2 s−1 under Fe‐limiting conditions. Steady‐state Fe uptake rates (ρSS) were also light dependent, increasing proportionally with growth irradiance for both Fe–ligand complexes. Photolysis of the Fe‐EDTA complex could explain the increase in ρSS in Fe‐EDTA‐amended medium because it increased [Fe(III)’], but it could not account for the faster rate of Fe uptake from FeDFB at high light because FeDFB is photostable. Short‐term Fe uptake rates measured in the absence of photochemically mediated Fe(III) reduction showed that cells preconditioned to high growth irradiance took up Fe faster than cells grown at low light. Thus, growth at high light induced a physiological response that increased Fe uptake. High growth irradiance also increased the rate of cellular Fe(III)’ reduction in the dark, similar to its stimulatory effect on short‐term Fe uptake. These results identify a previously unrecognized Fe–light interaction that could be important in enhancing Fe availability to diatoms. We suggest that the light effect could be the result of a light‐dependent regulation of cellular Fe(III) reduction.

Biomimetic photosynthetic system: Shedding light on the restoration of cell metabolism

Biomimetic photosynthetic system: Shedding light on the restoration of cell metabolism

Nursery optimization for kelp aquaculture in the Southern Hemisphere: the interactive effects of temperature and light on growth and contaminants

ABSTRACT Kelp aquaculture is typically a two-stage process, with an indoor nursery phase and a grow-out phase at sea. For the successful development and implementation of commercial kelp aquaculture, production of viable seeded lines in the nursery is essential. This study investigated optimal nursery conditions of three kelp species native to Tasmania, Australia: Ecklonia radiata, Lessonia corrugata, and Macrocystis pyrifera. The interactive effects of temperature (12°C, 15°C, and 18°C) and light level (~30 µmol photons s−1 m−2, and ~ 60 µmol photons s−1 m−2) on sporophyte length, sporophyte density, and contamination of spools were examined over a 34-day period. The optimal temperature and light levels were 15°C and 30 µmol photons m−2 s−1 for E. radiata, 12°C and 60 µmol photons m−2 s−1 for L. corrugata, and 12°C and 30 or 60 µmol photons m−2 s−1 for M. pyrifera. Under these optimal conditions, the mean ± SEM sporophyte lengths after 34 days were 0.60 ± 0.02 mm, 1.04 ± 0.04 mm, and 0.60 ± 0.01 mm for E. radiata, L. corrugata, and M. pyrifera, respectively. The mean ± SEM sporophyte densities for each of these three species were 15.5 ± 6.2 sporophytes cm−1 of line, 10.8 ± 5.9 sporophytes cm−1 of line, and 19.3 ± 8.1 sporophytes cm−1 of line, respectively. Contamination increased with increasing temperature and was not significantly affected by light level. This work highlights the need for a species- and ecotype-specific approach in the nursery phase to ensure successful seaweed aquaculture outcomes in new regions of cultivation.

Effects of different biomass ratios of light-tolerant microalgae-nitrifying bacteria consortia on ammonia removal

Research on microalgae-nitrifying bacteria has increased due to their ability to remove nitrogen without expensive mechanical aeration. However, due to photosensitivity of nitrifying bacteria, their outdoor application in certain environments can lead to poor treatment performance or process breakdown. Hence, we developed a light-shielding hydrogel encapsulating nitrifying bacteria to form a light-tolerant microalgae-nitrifying bacterial consortium. The established light-tolerant microalgae-nitrifying bacteria consortium can successfully remove ammonia even under bright light conditions. Batch experiments were conducted using light-tolerant microalgae-nitrifying bacteria consortia under 500 µmol photons m−2 s−1 to evaluate the effects of biomass ratios on the microalgal growth and ammonia removal. The maximum specific growth rate of microalgae, i.e. 1.3 d−1 was obtained for a biomass ratio (microalgae: nitrifying bacteria) of 1:9. Multiple regression analysis also revealed that the abundance of nitrifying bacteria was associated with a higher ammonia removal efficiency than microalgae. These findings can be used to design an effective treatment process for removing high concentrations of ammonia by microalgae-nitrifying bacteria consortia exposed to intense light.

The photosynthetic function analysis for leaf photooxidation in rice

Photooxidative damage causes early leaf senescence and plant cell death. In this study, a light-sensitive rice cultivar, 812HS, and a non-light-sensitive cultivar, 812S, were used to investigate early leaf photooxidation. Leaf tips of 812HS exhibited yellowing under a light intensity of 720 µmol(photon) m-2 s-1, accompanied by a decrease in chlorophyll and carotenoids, but 812S was unaffected. The photosynthetic performance of 812HS was also poorer than that of 812S. The H2O2, O2*-, and malondialdehyde content increased sharply in 812HS, and associated antioxidant enzymes were inhibited. The degradation of core proteins in both PSI and PSII, as well as other photosynthesis-related proteins, was accelerated in 812HS. When shaded [180 µmol(photon) m-2 s-1], 812HS recovered to normal. Therefore, our findings suggested excess light disturbed the balance of ROS metabolism, leading to the destruction of the antioxidant system and photosynthetic organs, and thus triggering the senescence of rice leaves.

The alga Bracteacoccus bullatus (Chlorophyceae) isolated from snow, as a source of oil comprising essential unsaturated fatty acids and carotenoids

A unicellular alga isolated from snow in the Sierra Nevada Mountains (Spain) was characterised using a polyphasic approach. Comparative analysis of ITS2 rDNA secondary structures identified the new culture (CCALA 1120 Cepák and Lukavský Nova Hedwigia 94:163–173, 2012) as being conspecific with Bracteacoccus bullatus (Chlorophyceae). For the first time this study documented sexual reproduction as the pairing of gametes and also an-isogamy. Strain CCALA 1120 had a temperature optimum of growth about 21 °C and an irradiance optimum above 160 µmol photons m−2 s−1. It was cultivated in pilot-plant scale, using an open thin-layer photobioreactor in a greenhouse with only partial temperature control. After harvest, a high proportion of fatty acids was found (15.3% of dry mass) with linoleic (18:2ω-6) 18.3% and α-linolenic acids (18:3ω-3) 17.4% being the most abundant. Monounsaturated fatty acids accounted for about 30% with oleic (18:1ω-9) and vaccenic acids (18:1 ω-7) as the most prominent. The ratio of PUFA ω-6/ω-3 was 1:1.16, i.e. near to the ideal ratio of 1:1, as recommended by the World Health Organization. Biomass production was 2.67 g m–2 day−1 of dry weight, i.e. 0.2 g L−1 day−1. At the end of growth phase, total carotenoids made up 10.1 mg L−1. These results indicate that B. bullatus is suitable for production of a vegetable oil at lower temperatures (12–18 °C) and comprising a high content of unsaturated fatty acids.

Productivity, photosynthetic light-use efficiency, nitrogen metabolism and nutritional quality of C4 halophyte Portulaca oleracea L. grown indoors under different light intensities and durations.

Portulaca oleracea L. (known as purslane), is a nutritious facultative C4 halophyte. Recently, it has been successfully grown indoors under LED lightings by our team. However, basic understanding about the impacts of light on purslanes are lacking. This study aimed to investigate the effects of light intensity and duration on productivity, photosynthetic light use efficiency, nitrogen metabolism and nutritional quality of indoor grown purslanes. All plants were grown in 10% artificial seawater hydroponically under different photosynthetic photon flux densities (PPFDs) and durations and thus different daily light integrals (DLI). They are, L1 (240 µmol photon m-2 s-1, 12h, DLI = 10.368mol m-2 day-1); L2 (320 µmol photon m-2 s-1, 18h, DLI = 20.736mol m-2 day-1); L3 (240 µmol photon m-2 s-1, 24h, DLI = 20.736mol m-2 day-1); L4 (480 µmol photon m-2 s-1, 12h, DLI = 20.736mol m-2 day-1), respectively. Compared to L1, higher DLI promoted root and shoot growth and thus increased shoot productivity by 2.63-,1.96-, 3.83-folds, respectively for purslane grown under L2, L3, L4. However, under the same DLI, L3 plants (continuous light, CL) had significantly lower shoot and root productivities compared those with higher PPFDs but shorter durations (L2 and L4). While all plants had similar total chlorophyll and carotenoid concentrations, CL (L3) plants had significantly lower light use efficiency (Fv/Fm ratio), electron transport rate, effective quantum yield of PSII, photochemical- and non-photochemical quenching. Compared to L1, higher DLI with higher PPFDs (L2 and L4) increased leaf maximum nitrate reductase activity while longer durations increased leaf concentrations and total reduced nitrogen. There were no significant differences in leaf total soluble protein, total soluble sugar and total ascorbic acid concentrations in both leaf and stem regardless of light conditions. However, L2 plants had the highest leaf proline concentration but leaf total phenolic compounds concentration was higher in L3 plants instead. Generally, L2 plants had the highest dietary minerals such as K, Ca, Mg and Fe among the four different light conditions. Overall, L2 condition is the most suitable lighting strategy in enhancing productivity and nutritional quality of purslane.

Effect of the Enhanced Production of Chlorophyll b on the Light Acclimation of Tomato.

Tomato (Solanum lycopersicum Mill.) is one of the widely cultured vegetables under protected cultivation, in which insufficient light is one of the major factors that limit its growth, yield, and quality. Chlorophyll b (Chl b) is exclusively present in the light-harvesting complex (LHC) of photosystems, while its synthesis is strictly regulated in response to light conditions in order to control the antenna size. Chlorophyllide a oxygenase (CAO) is the sole enzyme that converts Chl a to Chl b for Chl b biosynthesis. Previous studies have shown that overexpressing CAO without the regulating domain (A domain) in Arabidopsis overproduced Chl b. However, the growth characteristics of the Chl b overproduced plants under different light environmental conditions are not well studied. Considering tomatoes are light-loving plants and sensitive to low light stress, this study aimed to uncover the growth character of tomatoes with enhanced production of Chl b. The A domain deleted Arabidopsis CAO fused with the FLAG tag (BCF) was overexpressed in tomatoes. The BCF overexpressed plants accumulated a significantly higher Chl b content, resulting in a significantly lower Chl a/b ratio than WT. Additionally, BCF plants possessed a lower maximal photochemical efficiency of photosystem II (Fv/Fm) and anthocyanin content than WT plants. The growth rate of BCF plants was significantly faster than WT plants under low-light (LL) conditions with light intensity at 50-70 µmol photons m-2 s-1, while BCF plants grew slower than WT plants under high-light (HL) conditions. Our results revealed that Chl b overproduced tomato plants could better adapt to LL conditions by absorbing more light for photosynthesis but adapt poorly to excess light conditions by accumulating more ROS and fewer anthocyanins. Enhanced production of Chl b is able to improve the growth rate of tomatoes that are grown under LL conditions, indicating the prospect of employing Chl b overproduced light-loving crops and ornamental plants for protected or indoor cultivation.

Photosynthetic electron transport in a tropical moss Hyophila involuta

Despite their global distribution moss physiology is not well understood, particularly in tropical environments. Photosynthetic Electron Transport Rate (ETR) of Hyophila involuta was measured using PAM technology. The plants were growing in a heavily shaded habitat with irregular sunflecks of full sunlight. Two models were used for estimating photosynthetic electron transport (ETR), the Waiting-in-Line and Eilers-Peeters models. Both take photoinhibition into account and gave similar results. The population studied was growing on bricks and stonework and so periodically dried out. The same species is sometimes found in waterfall environments where it is semi-aquatic. ETRmax was low at dawn, increased to an early morning maxima and then decreased during the course of the day, partially reversed by rainstorms. Mid-morning (10:30 solar time): Eopt ≈ 521 ± 77 µmol photon m–2 s–1 which is higher than might be expected in a shaded sun-fleck environment, ETRmax ≈ 28.3 ± 2.5 µmol e- m–2 s–1 on a projected surface area basis or ≈ 57.7 ± 5.1 (µmol e- g–1 Chl a s–1), photosynthetic efficiency (Alpha, α0) ≈ 0.301 (e- photon–1 g–1 Chl a). Chl a content of Hyophila was ≈ 453 mg Chl a m–2 with Chl b/a ≈ 0.371. The O2 electrode-based respiration rate was R = 6.78 ± 0.698 µmol O2 g–1 Chl a s–1, the ETRmax is roughly equivalent to Gross photosynthesis (Pg) ≈ 14.4 ± 1.28 µmol O2 g–1 Chl a s–1 (4 e-/ O2), so the optimum Pg/R ratio is about 2.12 ± 0.289 and net photosynthesis (Pn) is ≈ 7.62 ± 1.46 µmol O2 g–1 Chl a s–1. Thus even under optimum irradiance net photosynthesis was actually rather low. pH experiments showed that Hyophila used both CO2 & HCO3- inorganic carbon sources, suggesting that a concentrating mechanism (CCM) is present. Hyophila is partially homiochlorophyllous, recovering well from desiccation after 2h of lighted rehydration and recovers more after 24h but lost ≈30% of its Chl a. The moss retained its chlorophyll content if desiccated in the dark. The moss lost ≈ 2/3 of its Chl a during the monsoonal dry season.

Integrated experimental and photo-mechanistic modelling of biomass and optical density production of fast versus slow growing model cyanobacteria

Biotechnological exploitation of fast-growing cyanobacterial species is hindered by unavailable mechanistic interpretations for the differing bioconversion rates when exploring strains with similar metabolic pathways and transport systems. This study investigated two strains: Synechococcus sp. PCC 11901, the fastest growing cyanobacterium identified to date, and Synechocystis sp. PCC 6803, under a range of operational light intensities from 300 to 900 μmol photons m−2 s−1, and presents three original contributions. Firstly, strain specific dynamic biomass and optical density (OD750nm) models were constructed incorporating sophisticated photo-mechanistic influences, previously unachieved in OD750nm. Secondly, bootstrapping parameter estimation with 3-fold cross validations was exploited to simultaneously identify the model parameters and confidence intervals, thus enabling probabilistic simulations and thorough validation against experimental data sets. Thirdly, presented mechanistic interpretations for the over two-fold faster growth of PCC 11901 versus PCC 6803 despite PCC 6803's high light utilisation efficiency. These findings will benefit upscaling of future cyanobacterial biotechnology applications and exploitation of Synechococcus sp. PCC 11901 for production of biomass and chemicals of industrial, nutritional and medical importance.

Early warning of MIB episode based on gene abundance and expression in drinking water reservoirs

Cellular 2-methylisoborneol (MIB) yield of cyanobacteria varies under different conditions according to culture studies and field investigations, the causal mechanism remains unclear and results in ineffective MIB prediction. Through an intensive field survey during an MIB episode produced by Pseudanabaena cinerea in QCS reservoir, we demonstrated that MIB synthesis (mic) gene abundance (DNA) and expression (RNA) might be useful as parameters for early warning of MIB production. It was found that the abundance of mic DNA and RNA peaked ahead of MIB concentrations by 10 and 7 days, respectively. In addition, the RNA abundance (R2 = 0.45, p < 0.01) showed a slightly higher correlation with MIB compared to DNA abundance (R2 = 0.37, p < 0.01), suggesting that the conditions for the growth of Pseudanabaena cinerea might be slightly different from those for mic gene expression, which was verified by a culture experiment. The highest cell growth was obtained under 36 μmol photons m−2 s−1, while the highest cellular MIB yield and mic gene expression level were obtained under 85 μmol photons m−2 s−1. Our results clearly supported that light intensity was the virtual regulator governing the mic gene expression within the controlled culture experiment and the actual MIB episode in the reservoir. Besides these results, we developed an early warning model using mic gene abundance as an indicator of MIB episodes, which was verified in two other reservoirs. Our findings highlight the effect of light intensity on mic gene expression and MIB synthesis and provide an early warning tool targeting MIB episode prediction, which therefore should be of importance for source water authorities.