Microplastic diversity drives increases antibiotic resistance genes in soil
Results from a recent paper
Here is the thing with microplastic: it’s never just one thing in the environment. It is always a collection of many different types of microplastics that accumulate in any one spot, reflecting the diversity of plastics we as humans use. This diversity of plastic particles has also been termed the microplastome.
But this is not the way we typically study these pollutants. We usually examine just one or a few different microplastic particle types, and typically they examined one-by-one whenever a study includes several of them. So we rarely ever in experiments collect data on what happens when many of these different types of plastics co-occur.
One of the things that are reasonably well-established in microplastic research is that these particles tend to enrich antibiotic resistance genes on their surfaces, compared to the abundance in the bulk soil. This seems to be a very general response, observed in many different kinds of environments, not just the soil. What we don’t know: what happens when there are several different kinds of microplastics present in the soil at the same time. Does the diversity of such microplastic particles have an effect on the abundance of antibiotic resistance genes (ARGs)?
A paper that is just out in Nature Communications tested just this, another collaboration with the excellent group of Yong-Guan Zhu. Here, different diversities of microplastics were examined, taking a pool of 12 different microplastics, and testing what happens when you have 1, 3 or 6 of them in the soil at the same time. The overall amount of microplastics in any plastic-treated soil was the same (meaning less was added of each in the 3 and 6 treatments compared to the single-microplastic case), so that the only difference was really the different types of plastics.
The results show clearly that there is an increase in ARGs from 1, over 3 to 6 microplastic types in the soils. The abundance and the richness of ARGs increased. And what’s more, also high-risk ARGs increased along the microplastic diversity gradient, and also the amount of virulence factor genes, and the amount of mobile genetic elements. This is all not good, because the virulence factor genes indicate potential pathogens, and the mobile genetic elements indicate the possibility of (further) spread of ARGs. There were changes in genes, changes in microbial community composition, and shifts in functional traits of the soil microbiome, all likely contributing to these observed effects.
The study also included a fungicide treatment and a plant diversity reduction treatment, these also tended to increase ARGs.
This study points to the necessity to measure diversity of microplastic concentrations, not just overall levels. Apparently, different things are happening in the soil microbiome when a soil is contaminated with a whole suite of microplastics. This story is getting more and more intricate the more research is being done…
Don't people know you can't grow plastic as you can't grow money? Stop putting it in the soil! Ok but seriously microplastics are everywhere and it is a problem!