RVA 600 Lactobacillus: A great lactic acid bacterial strain that will add a pleasant tangy sourness.  RVA 600 is a pure culture of Lactobacillus rhamnosus  which  has been shown in clinical studies to have many beneficial effects. These are homofermentative (only produces lactic acid, no carbon dioxide or ethanol) and are hop-sensitive.  For more pronounces souring add before you add your yeast.  You can sour to taste then add a yeast strain to outcompete the bacteria.  Again, hop sensitive so easy on them…or dry hop the heck out of it! You may also want to experiment with blending sour low hop beer with an ale strain beer.