The Journey of Antibiotic Resistance Genes in Wastewater Treatment

You're following the story of antibiotic resistance genes as they travel through a wastewater treatment plant. These genes, both inside (intracellular) and outside (extracellular) of bacteria, have different fates. When wastewater arrives at the plant, it carries a mix of these genes. Some are important for fighting clinical infections, while others help bacteria resist common antibiotics like aminoglycosides. As the wastewater goes through treatment processes, like the conventional activated sludge method or the membrane bioreactor process, something interesting happens. The number of extracellular genes increases, making up almost half of the total resistance genes by the time the water is treated. This means that while inside the bacteria, genes might be safe, the ones floating outside are more likely to spread. The types of these floating genes change too. In the treated water, they come mostly from the genes inside the bacteria in the treated water, not from the bacteria in the sludge. This is important because it shows that the treatment processes work differently for these two types of genes. Membrane bioreactor processes, for example, reduce the number of floating genes more than the conventional activated sludge method. So, the journey of these resistance genes isn't the same. They face different challenges and have different endings based on where they are and how they're treated.