Phytohormones and Effects on Growth and Metabolites of Microalgae: A Review

Evaluation of the effects of Chlorella vulgaris, Nannochloropsis salina, and Enterobacter cloacae on growth, yield and active compound compositions of Moringa oleifera under salinity stress

Application of Chlorella vulgaris, Nannochloropsis salina and Enterobacter cloacae has been reported to improve the growth of multiple plant species. Moringa oleifera is a medicinal plant found in Saudi Arabia. Its leaves, flowers and fruit have been used as food. Moringa oleifera is rich in rutin and gallic acid and many other bioactive compounds, which collectively contribute to its demonstrated range of pharmacological activities. In Saudi Arabia, the semi-arid and arid weather presents a significant challenge to agriculture. High salinity in cultivated land is a particular threat. We applied Chlorella vulgaris, Nannochloropsis salina, and Enterobacter cloacae at multiple salinities to Moringa oleifera to investigate their effects on the growth, yield, and photosynthetic pigment content. We also examined possible changes in the phytochemical composition. The application of Chlorella vulgaris, Nannochloropsis salina and Enterobacter cloacae enhanced plant growth and yield, while inhibition was observed at high (6000 ppm) salinity. The presence of Chlorella vulgaris and Nannochloropsis salina altered plant growth and yield and rutin and gallic acid content of Moringa oleifera plants grown in saline conditions. Microalgae species were recommended for use as a bio-fertiliser alternative to mainstream synthetic fertilisers.

The Use of Microalgae and Cyanobacteria in the Improvement of Agricultural Practices: A Review on Their Biofertilising, Biostimulating and Biopesticide Roles

The increase in worldwide population observed in the last decades has contributed to an increased demand for food supplies, which can only be attained through an improvement in agricultural productivities. Moreover, agricultural practices should become more sustainable, as the use of chemically-based fertilisers, pesticides and growth stimulants can pose serious environmental problems and lead to the scarcity of finite resources, such as phosphorus and potassium, thus increasing the fertilisers’ costs. One possible alternative for the development of a more sustainable and highly effective agriculture is the use of biologically-based compounds with known activity in crops’ nutrition, protection and growth stimulation. Among these products, microalgal and cyanobacterial biomass (or their extracts) are gaining particular attention, due to their undeniable potential as a source of essential nutrients and metabolites with different bioactivities, which can significantly improve crops’ yields. This manuscript highlights the potential of microalgae and cyanobacteria in the improvement of agricultural practices, presenting: (i) how these photosynthetic microorganisms interact with higher plants; (ii) the main bioactive compounds that can be isolated from microalgae and cyanobacteria; and (iii) how microalgae and cyanobacteria can influence plants’ growth at different levels (nutrition, protection and growth stimulation).

An Experimental Investigation on Tribological Behaviour of Tire-Derived Pyrolysis Oil Blended with Biodiesel Fuel

The demand for alternative fuels has risen in recent years due to the economic and environmental consequences of conventional fuels. In addition to engine characteristics, i.e., performance, combustion, and emission the lubricity of the considered fuel is an important parameter for its selection. This experimental study shows the tribological performance of the tire pyrolysis oil by using the four-ball tester. Waste tire pyrolysis oil was purified by using the distillation process. The experiment was conducted over 300 s at 40, 50, 63, and 80 kg load, 1800 rpm constant speed, and 27 °C temperature of all fuels on the ASTM D2266 standard. The tribological performance of the tire pyrolysis oil was compared with the BT10 (biodiesel 90%–tire pyrolysis oil 10%) and BT20 (biodiesel 80%–tire pyrolysis oil 20%) and biodiesel. The optical microscope is used to measure the wear scar diameter and then it is examined through a scanning electron microscope. In terms of greater load-carrying capacity, tire pyrolysis oil shows better anti-wear behaviour compared to biodiesel fuel. The wear scar diameter of BT10, BT20, and tire pyrolysis oil was 23.99%, 8.37%, and 32.62%, respectively, lower than the biodiesel fuel at 80 kg load. The SEM micrographs revealed that tire pyrolysis oil and BT10 displayed lower wear as compared to counterparts. Finally, it is concluded that BT10 is the most suitable fuel in terms of tribological performance.

The Role of Phytohormones in Enhancing Metal Remediation Capacity of Algae

Heavy metal (HM) contamination of the environment is a major issue worldwide, creating an ever-increasing demand for remediation techniques. Remediation with algae offers an ecologically safe, cost-effective, and efficient option for HM removal. Similar to plants, growth and development of algae are controlled by the hormonal system, where phytohormones are involved in HM tolerance and thus can regulate remediation ability; however, the underlying mechanisms of phytohormone function remain elusive. This review aims to draw a comprehensive model of phytohormone contributions to algal performance under HM stress. We focus on the mechanisms of HM biosorption, uptake and intracellular storage, and on how phytohormones interact with algal defence systems under HM exposure. We provide examples of successful utilization of algae in remediation, and of post-processing of algal materials. Finally, we discuss the advantages and risks of using algae for remediation. An in-depth understanding of these processes can inform effective HM remediation techniques.

Different Classes of Phytohormones Act Synergistically to Enhance the Growth, Lipid and DHA Biosynthetic Capacity of Aurantiochytrium sp. SW1

In the present study, the impact of eight phytohormones from six different classes on the growth, lipid and docosahexaenoic acid (DHA) biosynthetic capacity of Aurantiochytrium sp. SW1 (SW1) was evaluated. Kinetin (KIN), jasmonic acid (JA) and gibberellic acid (GA) significantly enhanced the growth and DHA production of SW1 by 16%-28% and 66%-84% in comparison to the control, respectively. The synergistic effect of these three phytohormones, evaluated by the response surface methodology (RSM), showed that a combination of 3.6 mg/L GA, 2.0 mg/L KIN and 20.0 mg/L JA further increased the growth and DHA production of SW1 by 16% to 28% and 22% to 36%, respectively, in comparison to the individual supplementation. The synergistic effect of these phytohormones was also shown to be time-dependent, where feeding at 24 h of cultivation led to 15%, 26% and 35% further increments in the biomass, lipid and DHA production in comparison to that of 0 h, respectively. The determination of stress markers, antioxidant enzymes and key enzymes involved in fatty acid biosynthesis aided to elucidate the potential mechanism underlying the improvement of growth and DHA production by SW1 at various times of feeding. Supplementation with the phytohormones at 24 h exhibited the maximum impact on reducing the level of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as augmented the antioxidants (superoxide dismutase and catalase) and key metabolic enzymes involved in lipogenesis (malic, glucose-6-phosphate dehydrogenase and ATP-citrate lyase) in comparison to the control and other time points. This study signifies the potential application of phytohormones for improving the growth, lipid and DHA production in Aurantiochytrium spp.

Triacontanol as a dynamic growth regulator for plants under diverse environmental conditions

Triacontanol (TRIA) being an endogenous plant growth regulator facilitates numerous plant metabolic activities leading to better growth and development. Moreover, TRIA plays essential roles in alleviating the stress-accrued alterations in crop plants via modulating the activation of the stress tolerance mechanisms. The present article critically focuses on the role of exogenously applied TRIA in morpho-physiology and biochemistry of plants for example, in terms of growth, photosynthesis, enzymatic activity, biofuel synthesis, yield and quality under normal and stressful conditions. This article also enlightens the mode of action of TRIA and its interaction with other phytohormones in regulating the physio-biochemical processes in counteracting the stress-induced damages in plants.

Enhanced coproduction of astaxanthin and lipids by the green microalga Chromochloris zofingiensis: Selected phytohormones as positive stimulators

Phytohormones comprise a variety of trace bioactive compounds that can stimulate cell growth and promote metabolic shifts. In the present work, a two-stage screening strategy was innovatively established to identify positive phytohormones for enhancement of astaxanthin and lipid coproduction in microplate-based cultures of mixotrophic Chromochloris zofingiensis. The results showed that auxins were the most efficient stimulators for astaxanthin accumulation. The maximum content of 13.1 mg/g and yield of 89.9 mg/L were obtained using indole propionic acid (10 mg/L) and indoleacetic acid (7.8 mg/L), representing the highest levels of astaxanthin in this microalga reported to date. Total lipids with the highest content (64.5% DW) and productivity (445.7 mg/L/d) were coproduced with astaxanthin using indoleacetic acid. Statistical analysis revealed close relations between phytohormones and astaxanthin and lipid biosynthesis. This study provides a novel original strategy for improving astaxanthin and lipid coproduction in C. zofingiensis using the selected phytohormones as positive stimulators.

Coupling of abiotic stresses and phytohormones for the production of lipids and high-value by-products by microalgae: A review

Microalgae can produce lipids and high-value by-products under abiotic stress conditions, including nutrient starvation, high light intensity, extreme temperature, high salinity and the presence of heavy metals. However, the growth and development of microalgae and the accumulation of metabolites may be inhibited by adverse stresses. In recent years, phytohormones have emerged as a topic of intense focus in microalgae research. Phytohormones could sustain the growth of microalgae under abiotic stress conditions. In addition, the combination of plant hormones and abiotic stresses could further promote the biosynthesis of metabolites and improve the ability of microalgae to tolerate abiotic stresses. This review primarily focuses on the regulatory effects of exogenous phytohormones on the biosynthesis of metabolites by microalgae under adverse environmental conditions and discusses the mechanisms of phytohormone-mediated cell growth, stress tolerance and lipid biosynthesis in microalgae under abiotic stress conditions.

Microalgae for the production of lipid and carotenoids: a review with focus on stress regulation and adaptation

Microalgae have drawn great attention as promising sustainable source of lipids and carotenoids. Their lipid and carotenoids accumulation machinery can be trigged by the stress conditions such as nutrient limitation or exposure to the damaging physical factors. However, stressful conditions often adversely affect microalgal growth and cause oxidative damage to the cells, which can eventually reduce the yield of the desired products. To overcome these limitations, two-stage cultivation strategies and supplementation of growth-promoting agents have traditionally been utilized, but developing new highly adapted strains is theoretically the simplest strategy. In addition to genetic engineering, adaptive laboratory evolution (ALE) is frequently used to develop beneficial phenotypes in industrial microorganisms during long-term selection under specific stress conditions. In recent years, many studies have gradually introduced ALE as a powerful tool to improve the biological properties of microalgae, especially for improving the production of lipid and carotenoids. In this review, strategies for the manipulation of stress in microalgal lipids and carotenoids production are summarized and discussed. Furthermore, this review summarizes the overall state of ALE technology, including available selection pressures, methods, and their applications in microalgae for the improved production of lipids and carotenoids.

Enhancing biomass and lipid accumulation in the microalgae Schizochytrium sp. by addition of fulvic acid and EDTA

Enhancing lipid productivity and reducing oxidative damage is essential for lipid overproduction in microalgae. In this study, addition of 20 mg/L fulvic acid (FA) resulted a 34.4% increase of lipid yield in Schizochytrium sp. Furthermore, the cooperative effect of FA and EDTA on cell growth and lipid production was investigated. The combined addition of 20 mg/L FA and 1.0 g/L EDTA yielded a maximal cell dry weight of 130.7 g/L and lipid productivity of 1.16 g/L/h, representing 36.4% and threefold increase over the non-supplemented group, respectively. Moreover, compared with the non-supplemented group, the combined addition strategy exhibited overall lower levels of reactive oxygen species and malondialdehyde, which accompanied with 66.7% and 81.9% higher superoxide dismutase and catalase activity, respectively. Furthermore, a 24.1–37.1% increase of malic enzyme and 19.4–25.2% decrease of phosphoenolpyruvate carboxylase activity was observed during the entire fermentation stage (0–108 h). Results suggested that the combined addition strategy not only enhanced lipid accumulation, but also prevented the lipid peroxidation.