I deal with diesel bug a lot in narrow boats. In twenty years as a car mechanic I never came across it! Cars normally get thru the fuel so quickly it never gets chance to grow. It's a problem in boats, plant and farm equipment mainly which sits around a lot. It'll only grow if you have water in the tank, it lives in the water and feeds off stuff in the diesel. It thrives on biodiesel so the new mixed stuff is worse for it. The biocides work well for mild cases it just kills it and it gets trapped in the filter. For severe cases the tank will need cleaning cos it'll keep clogging filters. It forms a black jelly like substance that is slightly acidic and can attack engine components! But like I said its rare in cars. Best thing is make sure you have no water in the fuel then it can't grow. You can get fuel additives that make the fuel hold the water in suspension and burn it. if it sits around a lot just treat the fuel with bug killer if you think you may have it in the tank. But don't let it get bad cos that's when it gets expensive. I've had to pressure wash fuel tanks before then Hoover em out to get rid of the bloody stuff