Biosurfactants in Plant Protection Against Diseases: Rhamnolipids and Lipopeptides Case Study

Abstract

Biosurfactants are amphiphilic surface-active molecules that are produced by a variety of microorganisms including fungi and bacteria. Pseudomonas, Burkholderia, and Bacillus species are known to secrete rhamnolipids and lipopeptides that are used in a wide range of industrial applications. Recently, these compounds have been studied in a context of plant-microbe interactions. This mini-review describes the direct antimicrobial activities of these compounds against plant pathogens. We also provide the current knowledge on how rhamnolipids and lipopeptides stimulate the plant immune system leading to plant resistance to phytopathogens. Given their low toxicity, high biodegradability and ecological acceptance, we discuss the possible role of these biosurfactants as alternative strategies to reduce or even replace pesticide use in agriculture.

Keywords: antimicrobial; elicitor; lipopeptides; plant immunity; plant pathogen; rhamnolipids.

FIGURE 1

Schematic representation of dual effects of rhamnolipids and lipopeptides: antimicrobial activities and plant defense induction. mc-3-OH-acyl building block of rhamnolipids is perceived by plant through the LORE receptor ①; Rhamnolipid could be sensed through their direct insertion in plasma membrane ②. Recognition of rhamnolipids leads to early signaling events like ion fluxes (Ca²⁺), reactive oxygen species production (H₂O₂) and MAPK phosphorylation cascade ③. These early responses trigger defense gene expression, probably through activation of transcription factors (TF) and hormonal signaling pathways ④. This leads to defense mechanisms like cell wall reinforcement and PR protein accumulation ⑤ triggering the resistance to the microbes ⑥. Plant immunity due to lipopeptides does not involve a protein receptor and rely on interaction between lipopeptides and the plant membrane ⑦. Both rhamnolipids and lipopeptides can also have direct antimicrobial effects through direct insertion into the microbial plasma membrane ⑧. These insertions trigger loss of cell morphology leading to pore formation ⑨. The pore formation causes cellular component leakage triggering microbial cell death ⑩. Cell death due to lipopeptides can also be indirectly due to the inhibition or activation of microbial cell functions .