The work describes the interactions of nanosilver (NAg) with bacterial cell envelope components at molecular level and how this associates with the reactive oxygen species (ROS)-mediated toxicity of the nanoparticle. Major structural changes were detected in cell envelope biomolecules as a result of damages in functional moieties, such as the saccharides, amides and phosphodiesters. NAg exposure disintegrates the glycan backbone in the major cell wall component peptidoglycan, causes complete breakdown of lipoteichoic acid as well as disrupting the phosphate-amine and fatty acid groups in phosphatidylethanolamine, a membrane phospholipid. Consistent with oxidative attacks, we propose that the observed cell envelope damages are inflicted, at least in part, by the reactive oxygen radicals being generated by the nanoparticle during its leaching process, abiotically, without cells. The cell envelope targeting, especially those on the inner membrane phospholipid, is likely to then trigger the rapid generation of lethal levels of cellular superoxide (O2 ) and hydroxyl (OH ) radicals herein seen with a model bacterium. The present study provides a better understanding of the antibacterial mechanisms of NAg, whereby ROS generation could be both the cause and consequence of the toxicity, associated with the initial cell envelope targeting by the nanoparticle.
Nanosilver (Ag NPs) is currently one of the most commercialized antimicrobial nanoparticles with as yet, still unresolved cytotoxicity origins. To date, research efforts have mostly described the antimicrobial contribution from the leaching of soluble silver, while the undissolved solid Ag particulates are often considered as being microbiologically inert, serving only as source of the cytotoxic Ag ions. Here, we show the rapid stimulation of lethal cellular oxidative stress in bacteria by the presence of the undissolved Ag particulates. The cytotoxicity characteristics are distinct from those arising from the leached soluble Ag, the latter being locked in organic complexes. The work also highlights the unique oxidative stress-independent bacterial toxicity of silver salt. Taken together, the findings advocate that future enquiries on the antimicrobial potency and also importantly, the environmental and clinical impact of Ag NPs use, should pay attention to the potential bacterial toxicological responses to the undissolved Ag particulates, rather than just to the leaching of soluble silver. The findings also put into question the common use of silver salt as model material for evaluating bacterial toxicity of Ag NPs.
Food grade bioplastic has become a popular research topic these days. However, further studies are still required in order to develop bioplastic that has comparable mechanical and water barrier properties with synthetic plastic. In this research, to improve mechanical and water barrier properties of plant cellulose filled bioplastic, bacterial cellulose is added to create hybrid filler with banana pseudostem fibre in glycerol plasticized corn starch matrix. The filler banana pseudostem fibre and bacterial cellulose were first dispersed in mixture of glycerol and distilled water, starch was added and mixture was heated until gelatinization occured. The mixture was then casted and dried in oven. Research proved that 10wt% against starch mass was an optimum filler composition, which resulted in the highest mechanical strength of bioplastic. The utilization of hybrid filler showed a decrease in mechanical strength compared with bioplastic with single filler. The ratio of banana pseudostem:bacterial cellulose compotition in hybrid filler that gave the best mechanical properties was 25:75 which resulted in tensile strength 4.599 MPa and modulus 174.1 MPa. Although the utilization of hybrid filler did not improve the mechanical properties of bioplastic, the addition of bacterial cellulose was proven to give positive effect to water barrier properties. Bioplastic filled with hybrid 10wt% banana pseudostem fibre and 35wt% bacterial cellulose had water vapour transmission rate 3.8958 g/m2/hour. The mechanical and water barrier properties of bioplastic was confirmed with SEM, FTIR, and XRD analysis. Soil burial test for 9 days proved that banana pseudostem filler decreased 6.9% of corn starch bioplastic biodegradation rate.
Abstract-Utilizing whole-cell biocatalyst is a potential way to reduce catalyst cost in biodiesel production using lipase as catalyst. Whole-cell of Rhizopus oryzae was cultivated by one-step and two-step method and was immobilized on Biomass Support Particles (BSPs) and chitosan-TPP bead. Immobilized whole-cells on BSPs produce 11% (one-step) and 12% (two-step) FAME yield. While, FAME yield produced by immobilized whole-cell in chitosan-TPP beads are 23% (one-step) and 22% (two-step).
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