Microplastics – good for marine bacteria, bad for marine ecosystem functioning?

 Plastic pollution in our oceans is an ever looming threat to biodiversity within marine environments. Not only this but it has been found with increasing frequency in shellfish and so it is also becoming an issue for human health. Because of the abundance of plastic in the oceans it is important to understand how plastic interacts with the marine environment.

A study conducted by Galgani et al. in 2018 aimed to look at how polystyrene microplastics interacted with the marine environment and in particular with dissolved organic matter (DOM). Microcosms were set up containing DOM, bacteria and half contained polystyrene microplastics. Dom was measured along with the absorption of chromophoric dissolved organic matter (CDOM) which is a photo-reactive form of DOM; CDOM is produced naturally by marine bacteria by altering pre-existing DOM substrates.

It was found that in the presence of polystyrene microplastics, more CDOM was produced. This may be because the polystyrene acted as a good substrate for the formation of biofilms which would lead to an increase in bacterial activity. However, an increase in CDOM may have negative effects on the upper layers of the water column in oceans as CDOM absorbs light so it may change light conditions. In order to really assess the impacts of marine microplastic pollution pertaining to polystyrene, the effects of increased CDOM should be measured on photosynthetic marine organisms.

 

Galgani, L., Engel, A., Rossi, C., Donati, A., & Loiselle, S. A. (2018). Polystyrene microplastics increase microbial release of marine Chromophoric Dissolved Organic Matter in microcosm experiments. Scientific Reports, 8(1)

Fish guts - the key to preventing disease?

It has long been known that the gut microbiota of fish can greatly affect their susceptibility to certain pathogens. Many aquaculture farms are now opting to use probiotics and prebiotics to boost the gut microbiota of farmed fish to prevent disease rather than using antibiotics which can lead to antibiotic resistance arising within aquaculture systems.

Tran et al. conducted a study in 2018 with the aim of assessing whether there was a difference in the gut microbiota of grass carp (Ctenopharyngodon idellus) infected with an intestinal disease and that of healthy grass carp. These changes in gut microbiota were assessed through NGS-based 16S – rRNA sequencing.

It was found that there was a significant difference in the structures of microbial communities within the guts of healthy and diseased carp with members of the following genera being greatly increased in diseased fish: Dechloromonas, Methylocaldum, Planctomyces, Rhodobacter, Caulobacter, Flavobacterium, and Pseudomonas.

This study manged to shed light on the microbes associated with enteritis in carp which is a common disease found in fish in aquaculture operations that can frequently lead to death so this study has wide ranging implications for the early detection and prevention of this disease in aquaculture. However, quite a small group of fish were sampled, only 16, and the sampling was skewed towards diseased fish so by having more comprehensive and even sampling it may make the results more reliable and the results from the two groups more comparable.

Tran, N. T., Zhang, J., Xiong, F., Wang, G.-T., Li, W.-X., & Wu, S.-G. (2018). Altered gut microbiota associated with intestinal disease in grass carp (Ctenopharyngodon idellus). World Journal of Microbiology and Biotechnology, 34(6)