Algae and Their Metabolites as Potential Bio-Pesticides

Abstract

An increasing human population necessitates more food production, yet current techniques in agriculture, such as chemical pesticide use, have negative impacts on the ecosystems and strong public opposition. Alternatives to synthetic pesticides should be safe for humans, the environment, and be sustainable. Extremely diverse ecological niches and millions of years of competition have shaped the genomes of algae to produce a myriad of substances that may serve humans in various biotechnological areas. Among the thousands of described algal species, only a small number have been investigated for valuable metabolites, yet these revealed the potential of algal metabolites as bio-pesticides. This review focuses on macroalgae and microalgae (including cyanobacteria) and their extracts or purified compounds, that have proven to be effective antibacterial, antiviral, antifungal, nematocides, insecticides, herbicides, and plant growth stimulants. Moreover, the mechanisms of action of the majority of these metabolites against plant pests are thoroughly discussed. The available information demonstrated herbicidal activities via inhibition of photosynthesis, antimicrobial activities via induction of plant defense responses, inhibition of quorum sensing and blocking virus entry, and insecticidal activities via neurotoxicity. The discovery of antimetabolites also seems to hold great potential as one recent example showed antimicrobial and herbicidal properties. Algae, especially microalgae, represent a vast untapped resource for discovering novel and safe biopesticide compounds.

Keywords: algal extracts; antimicrobial; cyanobacteria; photosynthesis; plant defense.

Figure 1

The chemical structure of active compounds that were isolated from Sargassum wightii, Padina gymnospora, and Fischerella muscicola.

Figure 2

The chemical structures of active compounds that were isolated from Cladaphora fascicularis and Arthrospira platensis and other microalgae.

Figure 3

The chemical structure of active compounds that were isolated from Sphaerococcus coronopifolius, Plocamium cartilagineum, Plocamium telfairiae, and Prasiola crispa.

Figure 4

Algal polysaccharides with pesticidal action.

Figure 5

The chemical structures of active compounds that were isolated from Synechocystis aquatilis, Scytonema hofmanni, Nostoc sp., Microcystis aeruginosa, and Synechococcus elongatus.

Figure 6

The mode of action of photosynthesis inhibitors as shown on a simplified diagram of photosystem II within the thylakoid membrane. QA = primary quinone acceptor; QB = secondary quinone acceptor; PQ = plastoquinone; Pheo = pheophytin; P680 = photosystem II primary donor; TyrZ = tyrosine-Z radical.

Figure 7

Induction of plant defense responses via elicitors. Elicitors are recognized on the plasma membrane. Jasmonic acid (JA) biosynthesis starts with α-linolenic acid (18:3) or hexadecatrienoic acid (16:3) in the chloroplast. Conversion to JA takes place in the peroxisome [201]. Salicylic acid (SA) biosynthesis starts with chorismate in the chloroplast and SA is transported into the cytosol [202]. Ethylene (ET) biosynthesis starts with methionine and ET is recognized by receptors on the endoplasmic reticulum. All three pathways eventually lead to defense gene expression and evidence suggest crosstalk between these pathways [203].