Effects of carbon quantum dots on the growth of Lactobacillus plantarum ATCC 8014 due to oxidative stress and cell integrity destruction

Carbon quantum dots (CQDs) are readily enriched in organs due to their abundant functional groups, small particle size, and high water-solubility, however, their biological effects remain a controversial issue at present. In this study, CQDs were prepared by hydrothermal method with glycine and anhydrous D-glucose as raw materials, and their structure was characterized. Co-incubation of CQDs with Lactobacillus plantarum ATCC 8014 (L. plantarum ATCC 8014) revealed that as the concentration of CQDs increased, the scavenging effect of the fermentation supernatant from L. plantarum ATCC 8014 on ·OH, ·ABTS⁺ and ·DPPH decreased. After CQDs treatment, the cells exhibited morphological damage characterized by elongation, folding, fracture, and aggregation. Their tolerance to simulated gastrointestinal fluid was compromised, and the intracellular active substance lactate dehydrogenase leaked. Concurrently, the content of reactive oxygen species (ROS) in L. plantarum ATCC 8014 increased with the rising concentration of CQDs. The activity of antioxidases decreased, while the content of malondialdehyde (MDA), a product of lipid peroxidation, increased. Furthermore, the expression of antioxidant-related genes, including Gpx, Gsh and Cat, was down-regulated. These results suggest that exposure to CQDs adversely affects the growth of L. plantarum ATCC 8014 by inducing oxidative stress and compromising cell integrity.