[Music] as we move from the exponential to the stationary phase we enter a phase right here that's not on here that's referred to as the late log phase and in this phase if they're capable they will make endospores and they might also go through a process called transformation which we will talk about in an upcoming chapter and both of these are efforts for the cells to survive because as we enter this stationary phase equal numbers of cells are dividing but also dying so here we see no change in cell number there's no increase and there's no decrease because cells are dividing and dying and this phenomena is known as cryptic growth so in cryptic growth if possible subpopulations of cells will adapt and they will adapt to cannibalize and reuse resources from dying cells and that in particular is this process of transformation so they will try numerous things to try and adapt they will undergo molecular changes to their DNA trying to survive in this medium where they're running out of nutrients but toxic waste is now building up if the incubation continues and nothing changes the cells will enter the decline phase where cells will begin to die and in some cases that death is accompanied by cell liis this decline phase is also exponential but not as steep as the exponential growth rate that we saw here now in some cases we're also going to see a phenomena called prolonged decline or prolonged death or something like that there there's many different phrases for it and what this means is these cells are undergoing these genetic changes to try and survive in that stationary phase and they do survive but what we're seeing then is we see this kind of lag period and then we see exponential and then they run out of nutrients and then they die and then others are doing the same right behind them so you'll see this kind of continued growth curve happening as these cells try and adapt to whatever is left in this medium now if we want to maintain our cell population in exponential growth for extended periods we will use a continuous culture device otherwise known as a open system unlike the closed system that we just looked at and these are referred to as chemostats so chemostats are a means of maintaining our cultures in exponential growth now these are used to study microbial physiology ecology and evolution fresh medium is going to be supplied constantly at a particular rate so that's all worked out depending on generation time Etc um we will also provide sterile air or other types of gases depending on the microbial need and at the same time we will overflow flow any excess waste um any excess uh affluent that the microbial cells will release so we constantly be removing from that so that we're removing toxic compounds we're adding New Media we're adding new gases that allows these cultures to be maintained in that exponential phase