Fibers and fragments of microplastics conjugated with the bacterial pathogen A. salmonicida achromogenes affect the physiology, the behaviour and the gene expression of zebrafish (Danio rerio) larvae
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- To date, 8 billion tons of plastic have penetrated the environment as macroplastics which, after fragmentation, become microplastics (MPs) (< 5 mm). They have a wide variety of size, shape, polymer type, and concentration as well as different effects depending on those characteristics. Effects also depend on the presence of additives or biofilms which can use MPs as “Trojan horses” to penetrate the organism of aquatic beings. Danio rerio, also known as the zebrafish, has already been experimented on with MPs and bacteria conjugated. To further investigate the biological mechanisms underlying microplastics toxicity conjugated or not with a common aquatic pathogen, analysis were conducted on the effects of microplastics on zebrafish larvae at transcriptomic, physiological and behavioral level. Zebrafish larvae have been exposed to polyethylene terephtalate fragments and fibers (1000 μg/L) conjugated or not with the bacteria for 4 days. Fiber exposure supposedly caused edema of the yolk sac, swollen optic vesicle, greater head height as well as premature hatching and up-regulated tfa gene expression. Bacteria were responsible for higher heart rate at 48 and 96 hpf, and delayed hatching. Oxidative stress was supposedly so intense for all exposed groups, it was responsible for the down-regulation of cyp1a and sod. Swimming decreased during and after tapping for all groups except the control. Considering the findings reported, it was hypothesised that the effects of fibers exposure was more toxic than fragments and bacteria exposure. In addition bacteria had a differential effect on the larvae than MPs and showed no effect of synergy with them.