It is well known that organic pollutants can negatively impact humans and animals. But how do these pollutants affect bacteria, the very smallest organisms in the food web?
Text: Kristina Viklund
Bacteria play a key role in the marine ecosystems, using organic molecules as a source of nutrition and energy. Among other things, they have the ability to use dissolved organic carbon, which is one of the largest stocks of carbon in the seas. It would be conceivable that the bacteria could benefit from organic pollutants by breaking down and consuming organic molecules as food, unless the bacteria are adversely affected by the toxins. So far, knowledge about this is limited.
Previous studies have shown that both phytoplankton and cyanobacteria can be adversely affected by environmental pollutants, and cocktail effects have also been shown on these organism groups, that is, mixtures of toxins can have a greater impact than the sum of each individual substance.
Testing commonly occurring Baltic Sea bacteria
The EcoChange researchers investigated how organic pollutants affect marine bacteria. They chose to study a specific bacterium, Rheinheimera sp. BAL341. This bacterium is commonly found in the seas, and has previously been shown to respond to changes in the environment. The pollutant test groups were all chemicals found in the marine environment, such as PAHs, alkanes, organophosphates and PFAS. By examining both direct effects on growth and effects on the gene expression of the bacteria, the researchers expected to find both positive and negative effects.
Inhibited by toxins
However, results showed no positive effect on the growth of the bacteria. Instead, adverse effects were noted, suggesting that the chemicals had a toxic effect on the bacteria. When the bacteria were exposed to the toxins at the same concentrations as those found in the marine environment, the growth and production of the bacteria were inhibited.
The environmental toxins not only had a direct effect on the bacteria, but were also found to alter the gene expression of the bacteria. The toxins thus appeared to initiate processes in the bacteria, possibly in defense of the toxic effects of the substances.
We know that many microorganisms have genes to break down PAH substances, but that they still can be negatively affected by these substances. Rheinheimera sp BAL341 lacks the gene to break down PAHs, which may be an explanation for the negative impact the PAHs had on the bacterium.
PFAS is a group of substances that have only recently been recognized for their worldwide spread and persistence. There are many chemicals in this group, all of them very hard to break down. For example, there are no reports that PFOS and PFOA can be broken down under natural conditions. This is one explanation that the substances have spread so widely.
In the experiments with Rheinheimera sp BAL341, PFAS had no effect on the growth during the short time that the experiments were performed. However, a clear effect on gene expressions could be demonstrated. These results suggest that prolonged exposure, as is the case under natural conditions, could affect the growth of the bacterium. The results also show the value of using the modern technology for gene expression studies to detect environmental toxicity problems before they have effects on the ecosystem.
The article has earlier been published in the EcoChange annual report 2019. It is based on: