Polystyrene microplastics interaction and influence on the growth kinetics and metabolism of tilapia gut probiotic <i>Bacillus tropicus</i> ACS1

Gut probiotic bacteria play a significant role in the host health, immunity, and survival. In aquaculture, changes in the gut microbiome of fishes affect the overall productivity and product quality. In the scenario of growing plastic pollution and associated microplastic prevalence, the current study was designed to investigate the interactions and impact of prepared polystyrene microplastics (PS-MPs) of irregular surface morphology on a probiotic bacteria <i>Bacillus tropicus</i> ACS1, isolated from the gut of <i>Oreochromis mossambicus</i> (commonly called as Tilapia). The cell viability was significantly increased along with changes in bacterial growth kinetics upon exposure to varying concentrations of PS-MPs. The microplastic exposure also increased the production of exopolysaccharides (EPS) and induced slight changes in the IR spectra of the EPS. A peak representing a carbonyl linkage that could be attributed to the glycosidic linkages between sugars disappeared following exposure to higher concentrations of PS-MPs. The interaction between the bacteria and the microplastics was visualized using scanning electron microscopy (SEM) and the colonization of the bacteria with active biofilm formation was observed. The investigation of PS-MP induced oxidative stress in the bacteria revealed the generation of reactive oxygen species (ROS) and increase in anti-oxidant enzyme concentrations, superoxide dismutase (SOD), and catalase. The study provides new insights into the effect of microplastics on gut probiotics of an economically significant aquaculture species.