Bacterial Exopolysaccharide-Mediated Synthesis of Silver Nanoparticles and Their Application on Bacterial Biofilms

Abstract

The development of multi-drug-resistant bacteria and their biofilm formation capabilities has decreased the effectiveness of antibiotics and other antimicrobial agents. Silver nanoparticle (AgNP) is currently being explored as an alternative strategy in countering biofilm-related infections. In this study, AgNP was biosynthesized using the extracted exopolysaccharide (EPS) from two obligate alkaliphilic bacteria, Bacillus krulwichiae M2.5 and Bacillus cellulosilyticus M4.1, isolated from a hyperalkaline spring in Zambales, Philippines. The samples exhibited an absorption peak at around 420 nm corresponding to the surface plasmon resonance of AgNPs as shown by UV-Vis analysis. The Fourier transform infrared (FTIR) spectroscopy spectra revealed functional groups in the EPS such as hydroxyl and carboxyl involved in the reduction of Ag+ to AgNP. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) spectroscopy showed stable irregular and spherical AgNPs with an average size of 25.88 ± 10.49 nm and 23.99± 8.43 nm for B. krulwichiae M2.5 EPS-AgNP and B. cellulosilyticus M4.1 EPS-AgNP, respectively. The biosynthesized AgNPs significantly inhibited the biofilm formation of Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus in a dose-dependent manner as determined by microtiter plate assay. However, the results showed a reduced inhibitory effect of the synthesized AgNPs on established biofilms indicating the need for higher AgNP concentration. This study demonstrates that EPS from bacteria adapted to alkaline conditions can be used for efficient AgNP biosynthesis with potential biomedical applications.

Silver nanoparticles: Synthesis, medical applications and biosafety

“…The enzyme gains electron from NADH, oxidizes it to NAD + , and undergoes oxidation to reduce silver ions to AgNPs 18 , 109 . Some organic substances can also act as stabilizers and capping agents for AgNPs to prevent particle aggregation 18 , 110 . The mechanisms of bacteria-mediated synthesis of AgNPs still need to be further explored.…”

Green synthesis of AgCl/Ag3PO4nanoparticle using cyanobacteria and assessment of its antibacterial, colorimetric detection of heavy metals and antioxidant properties

“…The EPS was separated by centrifugation at 11,000 rpm for 20 min at 4°C. The precipitate was freeze‐dried [23, 24].…”

“…After that, the colour of the solution became dark grey, while the colour of the control did not change. Finally, the solution was dialysed using a regenerated cellulose tube (Mw cut‐off 14,000 Da) against deionised water for 48 h [23, 24].…”

“…virescens ) [14] and Pseudomonas aeruginosa [15], fungi, such as Aspergillus [16] and Fusarium [17], microalgae [18] and cyanobacteria [19] and in addition plant extracts [20], plant root extract [21] and macroalgae [22] have been used for metal NPs synthesis. Additionally, several studies have reported the production of NPs by some biomolecules of bacteria [23, 24] and microalgae [25] such as exopolysaccharides (EPSs).…”

The Emerging Trend of Bio-Engineering Approaches for Microbial Nanomaterial Synthesis and Its Applications

“…Moreover, the EPS production can be tailor made using genetic, molecular, and other biotechnology tools. Succinoglycan, levan, and cellulose based EPS have been shown to act as reducing and/or stabilizing agents for the synthesis of metallic NPs (Galvez et al, 2018;Gonzalez-Escarcega et al, 2018). The means by which biofilms are crucial in synthesizing as well as stabilizing nanoparticles are depicted in Figure 5.…”