Exploring the Behavior and Metabolic Transformations of SeNPs in Exposed Lactic Acid Bacteria. Effect of Nanoparticles Coating Agent.

Maria Palomo-Siguero,Yolanda Madrid

doi:10.3390/ijms18081712

Abstract

The behavior and transformation of selenium nanoparticles (SeNPs) in living systems such as microorganisms is largely unknown. To address this knowledge gap, we examined the effect of three types of SeNP suspensions toward Lactobacillus delbrueckii subsp. bulgaricus LB-12 using a variety of techniques. SeNPs were synthesized using three types of coating agents (chitosan (CS-SeNPs), hydroxyethyl cellulose (HEC-SeNPs) and a non-ionic surfactant, surfynol (ethoxylated-SeNPs)). Morphologies of SeNPs were all spherical. Transmission electron microscopy (TEM) was used to locate SeNPs in the bacteria. High performance liquid chromatography (HPLC) on line coupled to inductively coupled plasma mass spectrometry (ICP-MS) was applied to evaluate SeNP transformation by bacteria. Finally, flow cytometry employing the live/dead test and optical density measurements at 600 nm (OD600) were used for evaluating the percentages of bacteria viability when supplementing with SeNPs. Negligible damage was detected by flow cytometry when bacteria were exposed to HEC-SeNPs or CS-SeNPs at a level of 10 μg Se mL−1. In contrast, ethoxylated-SeNPs were found to be the most harmful nanoparticles toward bacteria. CS-SeNPs passed through the membrane without causing damage. Once inside, SeNPs were metabolically transformed to organic selenium compounds. Results evidenced the importance of capping agents when establishing the true behavior of NPs.

Highlights

Nanomaterials are currently employed in many fields such as science, technology and even consumer products
Synthesis of Selenium nanoparticles (SeNPs) was carried out by applying a chemical process developed by Bai et al [11] that is based on the reduction of selenite with ascorbic acid in presence of different stabilizers agents (Chitosan, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylated and Hydroxyethyl cellulose)
The results showed that the stabilizers employed provided spherical SeNPs of similar diameters, allowing us to examine the toxicity of SeNPs against the nature of the

Summary

Introduction

Nanomaterials (within 1 nm to 100 nm size) are currently employed in many fields such as science, technology and even consumer products. A huge number of studies are associated with elucidating the toxicity mechanisms of NPs. The proposed mechanisms include: interaction of NPs with cell membranes producing physical damage, NP internalization resulting in cell malfunction, production of reactive oxygen species, and inhibition of protein function [1,2]. NP toxicity is affected by parameters such as, size, morphology, chemical composition and the nature of the stabilizer. It is accepted that the fate and toxicity of NPs are largely influenced by the physical interaction between the NP surface and the cellular membranes or bacteria examined. The use of stabilizers may hinder the normal utilization of synthesized nanoparticles in biological applications since their chemical nature may be toxic. These data suggest that size alone is not the exclusive determining toxicity factor. NPs will be subjected to dynamic physical and chemical conditions which result in transformation to different end-products

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