Direct effects of organic pollutants (OPs) on the growth and gene expression of the Baltic Sea model bacterium Rheinheimera sp. BAL341. Additional genomes from Baltic isolates: BAL289 BAL336 BAL341 BAL352 BAL450 BAL337 BAL334. Baltic Sea bacterial isolate genomes

Organic pollutants (OPs) are organic chemical compounds that are bioaccumulative, toxic, globally widespread and resistant to environmental degradation. Research shows that OPs have negative influence on aquatic wildlife. Although marine bacteria are major drivers of the ocean carbon cycle and vital elements there is limited knowledge about OPs effects on heterotrophic bacterioplankton. To explore such potential effects, the Baltic Sea model bacterium Rheinheimera sp. BAL341 was exposed to selected model molucules of OPs in exponential and early stationary growth phases. The selected OPs consisted of a mix of semi-volatile (**or non-polar) OPs: polycyclic aromatic hydrocarbons (PAHs), alkanes and organophosphates (OPEs), here referred to as MIX. We also investigated ionic fluorinated (or polar) POPs the perfluorooctanesulfonic acids (PFOSs) and perfluorooctanoic acids (PFOAs), here referred to as PFC. During exponential growth, the MIX pollutants resulted in a significant decrease (between 9-18%) in bacterial abundance and production compared to controls. Interestingly, both MIX and PFC induced notable shifts in gene expression profiles compared to controls. A majority of the significant genes were involved in the basic metabolism associated with growth. For the MIX, this was in agreement with the OPs influencing growth rates. However, given that PFCs did not significantly affect growth, the extensive gene expression response to PFCs was noteworthy, but could possibly indicate that bacterial responses to PFCs are more cryptic or delayed in time. Still, several responsive genes were involved in general stress responses (e.g. genes in the cold shock response) and others were highly specific to the investigated pollutants. The latter included the alkane-1 monooxygenase gene - a key gene in alkane degradation - which showed significantly higher relative expression levels in the MIX. The substantial direct influence of OPs on bacterial metabolism, as indicated by the gene expression responses, suggests that OPs could severely alter biogeochemical processes governed by marine bacterioplankton. Determining the generality of such influence represents an important future quest.