Abstract
Silver get washed into sewerage systems and eventually to wastewater treatment plant (WWTP) due to its utilization in industries. This poses concerns about the toxicity of these particles to microorganisms which are involved in biodegradation of organic wastes in biological WWTP. Pseudomonas species (Biosensor cell A, B, C, D and E) originally isolated from WWTP and modified by incorporating a stable chromosomal copy of the lux operon (lux CDABE) derived from <i>Escherichia coli</i> S17ƛ pir were sensitive immediately upon addition of silver nanoparticles (AgNPs) and bulk silver in short terms of incubation ranging from 0 to 300minutes. Microtitre plate luminometre was used to generate detailed luminescence reduction data for the silver particles tested against the bacterial cells in various concentrations ranging from 9µg/ml to 2500µg/ml. The EC<sub>50</sub> values generated at various time points showed that the highest toxicity was observed at time point, 0 of incubation for both AgNPs and bulk silver (158µg/ml and 618µg/ml EC<sub>50</sub> values respectively); these EC<sub>50</sub> values also indicate that AgNPs are much more toxic than bulk silver. Two putative biosensors, E and D showed proportional responses of bioluminescence reduction with increasing toxicant concentrations up to 2500µg/ml, hence displaying dose-dependent responses, superior operational range and sensing capabilities; good features for toxicity assay. Therefore, the recombinant isolate can be used to assay the toxicity of silver particles.
Highlights
Silver nanoparticles make up the largest portion of nano-materials used in consumer products and has been found in over 300 products globally which make up approximately 30% of known nanoparticles-containing products [1]
Silver nanoparticles appeared to elicit a larger response from the two transconjugants, E and D than bulk silver; silver nanoparticles at the concentrations of 625, 1250, 2500μg/ml caused a 100% reduction of luminescence output of both E and D (Figure 2 a and c) at time 0 to 300 minutes with even 312μg/ml causing 100% luminescence reduction in D (Figure 2c) while bulk silver at various concentrations did not lead to 100% reduction of light output from transconjugant E (Figure 2b) but caused complete bioluminescence reduction with transconjugant D at a concentration of 2500μg/ml at time 0 to 300minutes (Figure 2d)
AgNPs appeared to elicit a larger response from the two transconjugants, E and D than bulk silver; silver nanoparticles at the concentrations of 625, 1250, 2500μg/ml caused a 100% reduction of luminescence output from both E and D (Figure 2 a and c) at time 0 to 300 minutes with even 312 μg/ml causing 100% luminescence reduction indicating that D is more susceptible to the toxicant than E (Figure 2c) whereas this is much less the case for bulk silver; bulk silver at various concentrations did not lead to 100% reduction of light output from transconjugant E (Figure 2b) but caused complete bioluminescence reduction with transconjugant D at a concentration of 2500μg/ml at time 0 to 300minutes (Figure 2d)
Summary
Silver nanoparticles make up the largest portion of nano-materials used in consumer products and has been found in over 300 products globally which make up approximately 30% of known nanoparticles-containing products [1]. There have been different studies on the synthesis, use and release of nanoparticles (such as silver materials) into the environment. It has been reported that the released nanoparticles end up in the wastewater systems and subsequently gets into biological WWTP [3]. [4] reports that nano-silver releases ions when in contact with water and in aerobic conditions its anti-microbial effect could be greater in aquatic than in terrestrial environments. Environment condition is a determinant in the level of toxicity of nanosilver. [5] reports that autochthonous (indigenous) microorganisms are the most suitable for toxicity testing with prospective for in-situ relevance. Environment condition is a determinant in the level of toxicity of nanosilver. [5] reports that autochthonous (indigenous) microorganisms are the most suitable for toxicity testing with prospective for in-situ relevance.
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