Effect of TiO2 on Selected Pathogenic and Opportunistic Intestinal Bacteria

Elucidating the effect of TiO2 nanoparticles on mung bean rhizobia via in vitro assay: Influence on growth, morphology, and plant growth promoting traits

Titanium dioxide nanoparticles (TiO2 NPs) are among the most commonly used nanomaterials and are most likely to end up in soil. Therefore, it is pertinent to study the interaction of TiO2 NPs with soil microorganisms. The present in vitro broth study evaluates the impacts of low-dose treatments (0, 1.0, 5.0, 10.0, 20.0, and 40.0 mg L-1 ) of TiO2 NPs on cell viability, morphology, and plant growth promoting (PGP) traits of rhizobia isolated from mung bean root nodule. Two types of TiO2 NPs, that is, mixture of anatase and rutile, and anatase alone were used in the study. These TiO2 NPs were supplemented in broth along with a multifunctional isolate (Bradyrhizobium sp.) and two reference cultures. The exposure of TiO2 (anatase+rutile) NPs at low concentrations (less than 20.0 mg L-1 ) enhanced the cell growth, and total soluble protein content, besides improving the phosphate solubilization, Indole-3-acetic acid (IAA) production, siderophore, and gibberellic acid production. The TiO2 (anatase) NPs enhanced exopolysaccharide (EPS) production by the test rhizobial cultures. The radical scavenging assay was performed to reveal the mode of action of the nano-TiO2 particles. The study revealed higher reactive oxygen species (ROS) generation by the TiO2 (anatase) NPs as compared with TiO2 (anatase+rutile) NPs. Exposure to TiO2 NPs also altered the morphology of rhizobial cells. The findings suggest that TiO2 NPs could act as promoters of PGP traits of PGP bacteria when applied at appropriate lower doses.

Adverse effects of titanium dioxide nanoparticles on beneficial gut bacteria and host health based on untargeted metabolomics analysis

Titanium dioxide (TiO2) is a common additive in foods, medicines, and personal care products. In recent years, nano-scale particles in TiO2 additives have been an increasing concern due to their potential adverse effects on human health, especially gut health. The objective of this study was to determine the impact of titanium dioxide nanoparticles (TiO2 NPs, 30 nm) on beneficial gut bacteria and host response from a metabolomics perspective. In the in vitro study, four bacterial strains, including Lactobacillus reuteri, Lactobacillus gasseri, Bifidobacterium animalis, and Bifidobacterium longum were subjected to the treatment of TiO2 NPs. The growth kinetics, cell viability, cell membrane permeability, and metabolomics response were determined. TiO2 NPs at the concentration of 200 μg/mL showed inhibitory effects on the growth of all four strains. The confocal microscope results indicated that the growth inhibitory effects could be associated with cell membrane damage caused by TiO2 NPs to the bacterial strains. Metabolomics analysis showed that TiO2 NPs caused alterations in multiple metabolic pathways of gut bacteria, such as tryptophan and arginine metabolism, which were demonstrated to play crucial roles in regulating gut and host health. In the in vivo study, mice were fed with TiO2 NPs (0.1 wt% in diet) for 8 weeks. Mouse urine was collected for metabolomics analysis and the tryptophan metabolism pathway was also significantly affected in TiO2 NPs-fed mice. Moreover, four neuroprotective metabolites were significantly reduced in both in vitro bacteria and in vivo urine samples. Overall, this study provides insights into the potential adverse effects of TiO2 NPs on gut bacteria and the metabolic responses of both bacteria and host. Further research is needed to understand the causality between gut bacteria composition and the metabolism pathway, which is critical to monitor the gut-microbiome mediated metabolome changes in toxicological assessment of food components.

Smoothies Reduce the “Bioaccessibility” of TiO2 (E 171) in the Model of the In Vitro Gastrointestinal Tract

The food colorant E171 (TiO₂) containing nano fractions can cause potential health problems. In the presented work, we used a “gastrointestinal tract” model (oral→large intestine) to “digest” a fruit smoothie in the presence of TiO₂ nanoparticles and the Lactiplantibacillus plantarum B strain. The TiO₂ migration was measured using the microfiltration membrane (0.2 µm; model of “TiO₂ bioacessability”). We observed that the addition of the smoothie reduced the Ti content in the microfiltrate (reduced “bioacessability”) at the “mouth”, “stomach” and “large intestine” stages, probably due to the entrapment of Ti by the smoothie components. A significant decrease in Ti “bioaccessibility” at the “gastric” stage may have resulted from the agglomeration of nanoparticles at a low pH. Additionally, the presence of bacterial cells reduced the “bioaccessibility” at the “large intestine” stage. Microscopic imaging (SEM) revealed clear morphological changes to the bacterial cells in the presence of TiO₂ (altered topography, shrunk-deformed cells with collapsed walls due to leakage of the content, indentations). Additionally, TiO₂ significantly reduced the growth of the tested bacteria. It can be stated that the interactions (most probably entrapment) of TiO₂ in the food matrix can occur during the digestion. This can influence the physicochemical properties, bioavailability and in vivo effect of TiO₂. Research aimed at understanding the interactions between TiO₂ and food components is in progress.