Synergistic Activity of Rhamnolipid Biosurfactant and Nanoparticles Synthesized Using Fungal Origin Chitosan Against Phytopathogens

Abstract

Phytopathogens pose severe implications in the quantity and quality of food production by instigating several diseases. Biocontrol strategies comprising the application of biomaterials have offered endless opportunities for sustainable agriculture. We explored multifarious potentials of rhamnolipid-BS (RH-BS: commercial), fungal chitosan (FCH), and FCH-derived nanoparticles (FCHNPs). The high-quality FCH was extracted from Cunninghamella echinulata NCIM 691 followed by the synthesis of FCHNPs. Both, FCH and FCHNPs were characterized by UV-visible spectroscopy, DLS, zeta potential, FTIR, SEM, and Nanoparticle Tracking Analysis (NTA). The commercial chitosan (CH) and synthesized chitosan nanoparticles (CHNPs) were used along with test compounds (FCH and FCHNPs). SEM analysis revealed the spherical shape of the nanomaterials (CHNPs and FCHNPs). NTA provided high-resolution visual validation of particle size distribution for CHNPs (256.33 ± 18.80 nm) and FCHNPs (144.33 ± 10.20 nm). The antibacterial and antifungal assays conducted for RH-BS, FCH, and FCHNPs were supportive to propose their efficacies against phytopathogens. The lower MIC of RH-BS (256 μg/ml) was observed than that of FCH and FCHNPs (>1,024 μg/ml) against Xanthomonas campestris NCIM 5028, whereas a combination study of RH-BS with FCHNPs showed a reduction in MIC up to 128 and 4 μg/ml, respectively, indicating their synergistic activity. The other combination of RH-BS with FCH resulted in an additive effect reducing MIC up to 128 and 256 μg/ml, respectively. Microdilution plate assay conducted for three test compounds demonstrated inhibition of fungi, FI: Fusarium moniliforme ITCC 191, FII: Fusarium moniliforme ITCC 4432, and FIII: Fusarium graminearum ITCC 5334 (at 0.015% and 0.020% concentration). Furthermore, potency of test compounds performed through the in vitro model (poisoned food technique) displayed dose-dependent (0.005%, 0.010%, 0.015%, and 0.020% w/v) antifungal activity. Moreover, RH-BS and FCHNPs inhibited spore germination (61–90%) of the same fungi. Our efforts toward utilizing the combination of RH-BS with FCHNPs are significant to develop eco-friendly, low cytotoxic formulations in future.

Biosurfactants’ multifarious functional potential for sustainable agricultural practices

“…The extensive use of chemicals undoubtedly has a negative impact not only on soil health but also on plant growth. Such challenges can be addressed through BS-based eco-friendly solutions to eradicate or reduce the load of plant pathogens ( Adnan et al, 2018 ; Chopra et al, 2020a ; Karamchandani et al, 2022a ). A variety of BSs, namely, rhamnolipid (RL), surfactin, mannosylerythritol lipids (MELs), sophorolipids (SL), trehalose lipids (TL), and cellobiose lipids (CL) have been described to have antimicrobial activity against phytopathogens (bacteria, fungi, viruses, insects, and larvae) ( Díaz De Rienzo et al, 2016 ; Valotteau et al, 2017 ; Kumar et al, 2021 ; Handore et al, 2022 ).…”

“…Warm or humid weather-associated infections such as pythium blight, yellow tuft (downy mildew), and pythium damping-off can be controlled by using fungicide MAXX ® . Alternatively, a more biocompatible strategy encompasses the formation of NPs using fungi ( Patil et al, 2021 ; Karamchandani et al, 2022a ).…”

“…Along with their surface-active properties, BSs also exhibit noticeable pesticidal and antimicrobial properties (Fracchia et al, 2015;Ceresa et al, 2021). This proves them as a prime candidate for leading the path toward the sustainable management of agricultural pests and pathogens and avoiding the use of chemical pesticides (Naughton et al, 2019;Kumar et al, 2021;Karamchandani et al, 2022a;Karamchandani et al, 2022b;Adetunji et al, 2022;Sánchez, C., 2022). BSs are promising suitable and sustainable alternatives to chemical or synthetic surfactants mainly due to their lower toxicity to the human system (Marchant and Banat, 2012b).…”

“…The presence of hydrophilic and hydrophobic moieties facilitates interactions between immiscible liquids of agricultural formulations which can be challenging in nature. Therefore, understanding the role of BSs as “biopesticides” presents huge opportunities in the global surfactant market ( Karamchandani et al, 2022a ; Karamchandani et al, 2022b ). Biological and eco-friendly approaches involving microorganisms, especially plant growth-promoting rhizobacteria (PGPR) and other autochthonous microbes, are often helpful in breaking down pollutants and converting them into non-toxic or low-toxic metabolites ( Gayathiri et al, 2022 ).…”

“…Biological and eco-friendly approaches involving microorganisms, especially plant growth-promoting rhizobacteria (PGPR) and other autochthonous microbes, are often helpful in breaking down pollutants and converting them into non-toxic or low-toxic metabolites ( Gayathiri et al, 2022 ). Sustainable agricultural strategies also include the use of biomaterials such as chitin and chitosan (CH) in agricultural formulations to replace the need for harsh chemicals ( Karamchandani et al, 2022a ; Karamchandani et al, 2022b ).…”