Briefing Document: Nanofiber Encapsulation of Pseudomonas aeruginosa for Sustained Mosquito Larvicide Release
Date: Received - 13 December 2024 | Accepted - 04 April 2025 | Published - 21 April 2025
Source: Excerpts from "Nanofiber encapsulation of
Pseudomonas aeruginosa for the sustained release of mosquito larvicides"
https://doi.org/10.1038/s41598-025-97400-w
1. Executive Summary:
This study investigates a novel approach for mosquito vector control using nanofiber encapsulation of the bacterium Pseudomonas aeruginosa. The research addresses the inadequacy of current vector control strategies in eliminating mosquito-borne diseases by developing a method for the sustained release of bacterial larvicides. P. aeruginosa was selected for its potent larvicide production compared to other tested Pseudomonas species. The study demonstrates that encapsulating P. aeruginosa in electrospun nanofibers protects the bacteria, mimicking natural biofilms, enhances their survival in aquatic environments, and allows for prolonged larvicide production without harming non-target organisms (guppy fish). This nanotechnology-based method shows promise for controlling mosquito larvae in various breeding habitats over extended periods, potentially reducing application frequency and costs.
2. Background and Problem Statement:
- Mosquito-borne diseases (malaria, dengue, chikungunya, Zika, etc.) pose a significant global health threat, affecting hundreds of millions annually.
- Existing vector control strategies, primarily chemical insecticides and environmental management, are often insufficient for complete vector elimination.
- Increased insecticide resistance and environmental concerns associated with chemical methods necessitate the development of novel, sustainable approaches.
- Biological control using bacteria like Bacillus thuringiensis var. israelensis and Bacillus sphaericus offers a safer alternative, but their efficacy depends on persistence in the environment.
- Sustained-release formulations of microbial larvicides are highly desirable to reduce application frequency and costs.
- Conventional immobilization techniques for sustained release often suffer from limitations like low diffusion and reduced microbial viability.
"Despite the rising global incidence of vector-borne diseases such as malaria, dengue, chikungunya, and Zika, existing vector control strategies remain inadequate for completely eliminating vectors from their breeding sites."
3. Key Findings and Concepts:
- Superiority of Pseudomonas aeruginosa: Among the tested Pseudomonas species (P. fluorescens and P. putida), P. aeruginosa demonstrated the most potent larvicidal activity against four major mosquito vectors: Aedes aegypti, Culex quinquefasciatus, Cx. tritaeniorhynchus, and Anopheles stephensi.
- "During the initial screening, Pseudomonas aeruginosa proved to be more effective than the other two tested species, P. fluorescens and P. putida, in producing potent larvicides and was therefore selected for nanofiber encapsulation studies."
- Nanofiber Encapsulation Technique: Electrospinning was used to create a thin fibrous material at the nanoscale (1 nm - 1 µm) from Pluronic F127 dimethacrylate (F127-DM) and polyethylene oxide (PEO) to encapsulate and immobilize live P. aeruginosa bacteria.
- "In the present study, we rectified the shortcomings of conventional immobilization by developing a thin fibrous material at the nanoscale level (typically between 1 nm and 1 µm) using electrospinning to encapsulate and immobilize live bacteria."
- Protection and Sustained Release: Nanofiber encapsulation shields the bacterial cells from environmental stress, mimicking natural biofilms, thereby enhancing their survival and prolonging larvicide production. The cross-linking of the nanofibers prevents their rapid dissolution in water.
- "This study aimed to encapsulate larvicide-producing bacteria in nanofibers designed to shield bacterial cells from environmental stress—mimicking natural biofilms—thereby enhancing their survival in aquatic habitats and prolonging larvicide production."
- Efficacy in Batch Systems (Container Breeding Habitats): Nanofiber-encapsulated P. aeruginosa demonstrated sustained larvicidal activity in batch systems (simulating stagnant water bodies). The spent water containing released metabolites remained lethal to all four tested mosquito species for at least 8 days.
- "In the batch system, the spent water with metabolites of P. aeruginosa was lethal to all the tested species of larvae, such as Ae. aegypti, An. stephensi, Cx. tritaeniorhynchus, and Cx. quinquefasciatus, to varying degrees... The larvicidal potency of the spent water either remained the same as observed on the first day or increased during the subsequent days of incubation."
- Reduced Efficacy in Continuous Systems (Flowing Water Habitats): In continuous flow systems (simulating paddy fields or tanks with water inflow), the larvicidal efficacy of the released metabolites declined over subsequent days, suggesting this method might be less effective in such environments.
- "However, in a continuous system, although the 100% mortality of the tested larvae, Ae. aegypti and An. stephensi was recorded on the first day, but the efficacy declined on subsequent days."
- Optimal Nanofiber Quantity: 1 gram of P. aeruginosa-encapsulated nanofiber per 1 liter of water was sufficient to produce larvicidal metabolites capable of causing 100% mortality in Ae. aegypti larvae within 24 hours.
- "Our present study showed that even 1 g of P. aeruginosa-encapsulated nanofiber was sufficient to produce larvicidal exotoxin metabolites that can kill all the available mosquito larvae in 1 L of medium or water."
- Viability and Cell Washout: The encapsulated bacteria remained viable within the nanofibers, and no significant release or washout of free bacterial cells into the surrounding water was detected.
- "As there were no bacterial colonies appeared in the agar plates inoculated with the spent water of the nanofiber encapsulated P. aeruginosa, it is confirmed that there were no free bacteria released from the encapsulated fiber into the spent water..."
- Storage Stability: Nanofiber-encapsulated P. aeruginosa retained its larvicidal efficacy for up to one month when stored at 3°C. However, efficacy declined with longer storage periods.
- "The larvicidal efficacy of the spent water collected from the nanofibers stored for up to 1 month had killed 100% of the larvae of Ae. aegypti at 100% concentration... However, storage of bacteria-encapsulated fiber beyond 1 month shows declining efficacy..."
- Non-Target Organism Safety: The metabolites released by the nanofiber-encapsulated P. aeruginosa showed no mortality in guppy fish (Poecilia reticulata) at concentrations effective against mosquito larvae, indicating target-specificity.
- "No mortality was observed in the guppy fishes (P. reticulata) used as non-target organisms during the three days of the experiment..."
- Identified Larvicidal Compounds: GC-MS analysis of the spent water identified several compounds released by the encapsulated bacteria, with oleic acid, octadecanoic acid, and 2-methyl-Z,Z-3, 13-Octadecadienol being the major constituents. These compounds, including fatty acids, have been previously reported to have larvicidal activity.
- "Based on the percentage area of the chromatograph, it was found that, the oleic acid (37.71%), followed by octadecanoic acid (29.97%), and 2-methyl-Z, Z-3, 13-Octadecadienol (17.06%) were the major contributors."
- Morphological Changes in Dead Larvae: Ae. aegypti larvae killed by the metabolites appeared pale greenish, distinct from the light yellow appearance of larvae killed by the chemical larvicide temephos.
4. Implications and Future Directions:
- Nanofiber encapsulation of P. aeruginosa presents a promising bio-engineered approach for sustained mosquito larval control, particularly in container breeding habitats.
- The method offers a potentially safer alternative to chemical insecticides due to its target-specificity and the absence of free bacterial release.
- Further research is needed to optimize the nanofiber materials and encapsulation process for enhanced longevity and efficacy in various environmental conditions.
- Addressing the current high production cost of nanofibers is crucial for the widespread adoption of this method in large-scale field applications.
- "However, the higher production cost of nanofiber still poses a barrier to widespread usage... For large-scale field usage in the future, we may require a huge quantity of P. aeruginosa encapsulated nanofibers. Hence, facilities need to be developed for producing cheap, cost-effective bacteria encapsulation methods in nanofiber for widespread usage of this method."
- Larger field-based trials are necessary to evaluate the real-world effectiveness and potential ecological impacts of this novel vector control strategy.
5. List of Abbreviations:
A comprehensive list of abbreviations used in the study is provided in the source document for reference.
6. Funding:
This study was supported by a grant from the Department of Science and Technology (DST)-Nanomission, Govt. of India.
7. Competing Interests:
The authors declare no competing interests.
This briefing document summarizes the key aspects of the provided research article, highlighting the innovative approach of using nanofiber-encapsulated Pseudomonas aeruginosa for sustained and targeted mosquito larvicidal activity. The findings suggest a potential new tool for integrated vector management strategies, particularly for container-breeding mosquitoes.