 Alright, hey everybody this is Dr. O. In this video we're going to talk about the pH and its effects on growth. We've already covered oxygen and temperature, these kind of things. So just real quickly the pH scale goes from 0 to 14, 7 is neutral, anything with a pH under 7 would be acidic, anything with a pH above 7 would be alkaline or basic. So an acid file is going to love an acidic environment, a neutral file is going to love that neutral pH area around 7 give or take, and an alkaline file is going to like more alkaline temperature. So first of all, there's a tremendous diversity with microorganisms there, organisms that grow anywhere basically. But we only care about the ones that like to grow in us and on our food, right? So most bacteria are going to grow at a pH between 6.5 and 7.5, makes sense, you know that's the world around us is like that, our bodies are like that, so make sure you note that, most bacteria like to grow between a pH of 6.5 and 7.5 hovering right around a neutral. There are very few microorganisms, very few bacteria that can grow under a pH of 4. So there are some acid files, there are some organisms that can grow at a pH of 1, but they're not going to grow in you or your food so we don't really care about them. The reason that we love the fact that a low pH will inhibit almost all microbial growth and especially pathogens, this is why fermenting your food is such a powerful food preservation method. So when you turn cabbage into sauerkraut or you make kimchi or make yogurt, these kind of things, fermenting things lowers the pH greatly because of all the lactic acid added to the food and that's what makes it a preservation method. I don't know how long a cabbage would keep sitting out or even in the refrigerator, but I've had sauerkraut that I keep in the fridge just to see how long it goes before it turns and it hasn't after years. So the fact that most microbes don't like a lower pH is the reason fermentation is such a great food preservation method. Right, just you know, molds and yeast, they generally can grow along a larger pH range but they generally like a pH closer to 5 to 6, so bacteria like 6.5 to 7.5 molds and yeast a little more acidic. One last really important thing, so whether you're trying to keep microbes alive in a lab or hoping they don't survive, remember that just like us, microorganisms produce acidic byproducts or acidic products or compounds as a byproduct of their own metabolism. So we generate acids that have to be dealt with, we have buffers, but then we have urinary and respiratory mechanisms to deal with those acids. Microbes basically spew them into environments. So as microbes are growing, they basically poison their own environment by spewing out acids which lowers the pH, which they don't like, so this is one of the main reasons that we don't live on a planet just a mile deep with bacteria. They poison their own environment by releasing these acidic byproducts that lower the pH. All right, so that is the effect that pH is going to have on microbial growth. Have a wonderful day. Be blessed.