Elsevier

Bioresource Technology

Volume 254, April 2018, Pages 23-30
Bioresource Technology

Temporal acclimation of Microchloropsis gaditana CCMP526 in response to hypersalinity

https://doi.org/10.1016/j.biortech.2018.01.062Get rights and content

Highlights

  • Growth of Microchloropsis gaditana was affected at high saline condition.

  • Salinity stress induced accumulation of carbohydrate by ∼1.7-fold.

  • Accumulation of neutral lipid increased by ∼4.6-fold in response to salinity.

  • Insights into photosynthetic acclimation of M. gaditana during hypersaline stress.

Abstract

Evaporation from culture ponds and raceways can subject algae to hypersalinity stress, and this is exacerbated by global warming. We investigated the effect of salinity on a marine microalga, Microchloropsis gaditana, which is of industrial significance because of its high lipid-accumulating capability. Both short-term (hours) and medium-term (days) effects of salinity were studied across various salinities (37.5, 55, 70 and 100 PSU). Salinity above 55 PSU suppressed cell growth and specific growth rate was significantly reduced at 100 PSU. Photosynthesis (Fv/Fm, rETRmax and Ik) was severely affected at high salinity conditions. Total carbohydrate per cell increased ∼1.7-fold after 24 h, which is consistent with previous findings that salinity induces osmolyte production to counter osmotic shock. In addition, accumulation of lipid increased by ∼4.6-fold in response to salinity. Our findings indicate a possible mechanism of acclimation to salinity, opening up new frontiers for osmolytes in pharmacological and cosmetics applications.

Introduction

With the ever-increasing human population, demand for fossil fuel has increased drastically over the past decade. The restricted availability of arable land poses a serious challenge to grow plants for second-generation biofuel. Another alternative is to use microalgae as a third-generation source for producing biofuel. Microalgae can grow under variety of conditions and can be cultivated even in recycled municipal wastewater. Algae require less water than their terrestrial counterparts and can synthesize valuable co-products which can be used for applications ranging from pharmaceutical to cosmological purposes (Specht and Mayfield, 2014, Wang et al., 2015). The biomass can be used as a feedstock for animals and fish (Duong et al., 2015, Pulz and Gross, 2004). Another interesting trait of microalgae is that they accumulate lipids during unfavourable conditions. This property has been studied under various abiotic stress conditions such as pH, light, temperature, nutrient limitation, etc., (Markou & Nerantzis, 2013). One of the limitations in this approach is that the growth rate becomes compromised during stress conditions, which makes the process uneconomical. However, bioprospecting strategies along with multi-stage extraction steps can make the whole process economically feasible (Stranska-Zachariasova et al., 2016).

A two-stage cultivation can also be employed to decouple growth and lipid accumulation (Ra et al., 2015), but including an additional unit operation increases the cost of bio-fuel production. This might be overcome by modelling the reaction, optimizing the extraction process and reactor design (Likozar and Levec, 2014, Likozar et al., 2016, Šoštarič et al., 2012). Rather than inducing nutrient limitation, a naturally occurring stress in open raceway ponds was employed to understand the acclimation strategy in M. gaditana. These shallow ponds are prone to evaporation during the day-time, particularly in tropical regions, which leads to increase in salinity of the culture medium. Varying salinity levels have shown to induce lipid accumulation in several Nannochlorpsis strains (Gu et al., 2012b, Martínez-Roldán et al., 2014).

Microchloropsis gaditana CCMP526, previously known as Nannochloropsis gaditana CCMP526, is a marine microalga known for its potential to accumulate high levels of lipid (∼50% dry cell weight) and a high eicosapentaenoic acid content (Fawley et al., 2015, Sukenik et al., 1989). Being a marine strain, CCMP526 is susceptible to changes in salinity in its natural environment. Effects of light, CO2, temperature and nitrate limitation have been very well documented in CCMP526 (Corteggiani Carpinelli et al., 2014, Figueroa et al., 1997, Huertas et al., 2000, Simionato et al., 2011), which shows a range of biochemical changes during adverse conditions. Several studies have focussed on the effect of salinity on the physiology of other marine microalgae (Johnson et al., 1968, Takagi and Yoshida, 2006) as well as freshwater strains (Husic and Tolbert, 1986, Yoshida et al., 2004). For example, the marine green alga Dunaliella tertiolecta has been reported to accumulate osmolytes in the form of glycerol (Avron, 1992) and also combat high salt conditions by excluding Na+ ions from its cells (Katz & Pick, 2001). Some species closely related to Microchloropsis gaditana such as Nannochloropsis oculata and Nannochloropsis salina have been shown to accumulate lipid during adverse conditions (Bartley et al., 2013, Gu et al., 2012b, Pal et al., 2011). However, relatively few studies have focussed on understanding the acclimation strategy of microalgae towards high salt conditions.

In this study, we aimed at understanding the time course of acclimation of CCMP526 to hypersaline conditions by focussing on changes in primary functions such as photosynthesis, pigment synthesis, carbohydrate and lipid accumulation during short-term (hours) and medium-term (several days) hypersaline stress.

Section snippets

Growth conditions

Microchloropsis gaditana CCMP526 was cultivated in 0.2 μm-filtered sea water (collected from the Gippsland Lakes, Gippsland, Victoria, Australia), supplemented with Guillard’s f/2 nutrients (Guillard, 1975) and 17 mM sodium nitrate, at 25 °C using 500 ml glass bottles (Schott Duran, Germany). Cultures (300 ml) were mixed by bubbling with sterile air (0.2 μm filtered) supplied at a flow rate of 2.5 L min−1. Illumination was provided at 150 μmol·photons·m−2·s−1 (Philips, TLD36W, Amsterdam, The

Growth under different salinity conditions

The growth of M. gaditana CCMP526 was strongly influenced by the salinity conditions (two-way ANOVA: F (3, 72) = 875.1, P < .0001) and cultivation time (two-way ANOVA: F (8, 72) = 1207, P < .0001). Dunnett’s multiple comparisons test revealed that the growth rate (cell number) was not significantly affected until after the first 6 h of inoculation (P > .05), except for the 55 PSU treatment at 30 min (P = .0011) and for the 100 PSU treatment at 30 min and 3 h (P = .0001 and .0428 respectively).

Conclusions

Our study reveals the acclimation strategy of M. gaditana CCMP526 to hypersaline conditions. Temporal analysis of growth, photosynthetic parameters and various biomolecules suggests that salinity can be employed to induce lipid accumulation in M. gaditana, which is of industrial importance. Additionally, high saline conditions induced production of carbohydrates and pigments which could be of high interest in pharmacological and cosmetics areas. The ability of CCMP526 to grow at high salinity

Acknowledgements

The authors acknowledge the technical support from the members of Prof. John Beardall’s lab. This work was supported by the IITB-Monash Research Academy, IITB, Mumbai, India; Reliance Industries Limited, India (IMURA0304).

Conflicts of interest

The authors declare that there is no conflict of interest.

References (49)

  • G. Markou et al.

    Microalgae for high-value compounds and biofuels production: a review with focus on cultivation under stress conditions

    Biotechnol. Adv.

    (2013)
  • C.H. Ra et al.

    Cultivation of four microalgae for biomass and oil production using a two-stage culture strategy with salt stress

    Renewable Energy

    (2015)
  • D. Simionato et al.

    Acclimation of Nannochloropsis gaditana to different illumination regimes: effects on lipids accumulation

    Bioresour. Technol.

    (2011)
  • M. Šoštarič et al.

    Growth, lipid extraction and thermal degradation of the microalga Chlorella vulgaris

    New Biotechnol.

    (2012)
  • M. Stranska-Zachariasova et al.

    Bioprospecting of microalgae: Proper extraction followed by high performance liquid chromatographic–high resolution mass spectrometric fingerprinting as key tools for successful metabolom characterization

    J. Chromatogr. B

    (2016)
  • M. Takagi et al.

    Effect of salt concentration on intracellular accumulation of lipids and triacylglyceride in marine microalgae Dunaliella cells

    J. Biosci. Bioeng.

    (2006)
  • H.M. Wang et al.

    Exploring the potential of using algae in cosmetics

    Bioresour. Technol.

    (2015)
  • K. Yoshida et al.

    Mitigation of osmotic and salt stresses by abscisic acid through reduction of stress-derived oxidative damage in Chlamydomonas reinhardtii

    Plant Sci.

    (2004)
  • A.R. Angell et al.

    Indirect and direct effects of salinity on the quantity and quality of total amino acids in Ulva ohnoi (Chlorophyta)

    J. Phycol.

    (2015)
  • M. Avron

    Osmoregulation

  • K.A. Bérubé et al.

    Effects of chronic salt stress on the ultrastructure of Dunaliella bioculata (Chlorophyta, Volvocales): mechanisms of response and recovery

    Eur. J. Phycol.

    (1999)
  • D. Campbell et al.

    Predicting light acclimation in cyanobacteria from nonphotochemical quenching of photosystem II fluorescence, which reflects state transitions in these organisms

    Plant Physiol.

    (1996)
  • M. Dubois et al.

    Phenol sulphuric acid method for carbohydrate determination

    Ann. Chem

    (1956)
  • V.T. Duong et al.

    High protein- and high lipid-producing microalgae from northern Australia as potential feedstock for animal feed and biodiesel

    Front. Bioeng. Biotechnol.

    (2015)
  • Cited by (0)

    View full text