Bacterial growth media (LB, TB, SOB, SOC, etc.)

Bacterial growth media! From Terrific Broth (TB) to Lysogeny Broth (LB) to Super Optimal Broth (SOB), there’s a whole menu of microbial cuisine to choose for when you want to feed bacteria in exchange for them doing things for you (like copying DNA or making proteins), with different types to meet bacteria’s different tastes and the desired tasks. So, let’s get to some media influencing! 

blog: https://bit.ly/bacterialgrowthmedia  text old, video new:

When I wrote this… “Today” I set up a couple of flasks of bacterial growth media (microbial cuisine)- one of LB and one of TB - to do overnight starter cultures that I will use tomorrow for inoculating more media to express a protein (adding a few mL of the starter culture to larger flasks of media, letting the cells grow, then inducing protein expression with IPTG as I talked about in a past post if you want more deets). Protein expression is just one of the things we use bacteria for in biochemistry - we also use them a lot for making copies of DNA for us. And we have to feed the bacteria in return for getting them to work for us (I mean, it is only fair!). We call their food media.  

We don’t give them 5-star cuisine, basically we want to spend as little money as possible while still giving them the nutrients they need. At a minimum, we need to give them a source of energy, something they can break down (catabolize) to make ATP - such things can be sugars, proteins, fats

In addition to breaking things down, they need to be able to make things like proteins and DNA (do the anabolic part of metabolism). This requires nutrients that provide the elements needed like carbon and nitrogen.

They can’t make everything they need, so we also need to give them anything they need that they can’t make themselves. If they can make something themselves, we say they’re AUTOTROPHIC for that thing. If they can’t make something themselves, we say they’re AUXOTROPHIC for that thing
- being auxotrophic is only a problem if you’re in conditions where you need that thing (we’re technically auxotrophic for making coffee but unless you’re someplace that you need coffee to live…)
If they have the same making ability as their parent, we say they’re PROTOTROPHIC for that thing

Sometimes, we feed them in liquid media, when we’re growing them in suspension - we can grow them in broth in culture tubes or flasks, usually at 37°C with shaking and plenty of breathing room

Other times, we embed this media into a gel made of agar (a sugar chain) - they don’t eat this sugar chain, it just gives the gel structure so the bacteria can grow on top of it as colonies and the gel can kinda hold a stock of food for them. http://bit.ly/agarbakery  

cool fact I learned - apparently the first gelling agent tried (by Robert Koch in 1881) was gelatin. But the bacteria ate it, and it also melted too easily. The wife of one of Koch’s associates, Angelina Fanny Eilshemus suggested he try agar and it worked well. The bacteria didn’t eat it, and it stayed solid (and didn’t kill the bacteria :P )

A lot of the time the media we put in there is LB which stands for LYSOGENY BROTH - sometimes initials for Luria, Lennox, or Luria & Bertani get credit for the name, but it really stands for LYSOGENY BROTH and its recipe was first published (by Giuseppe Bertani) in 1951. He was using it when studying lysogeny (a process where a bacteria-infecting virus called a bacteriophage (“phage”) inserts its own DNA into a bacteria’s DNA & bides its time until conditions are right for entering the lytic phage where it cuts itself out, makes lots of copies and bursts open the cell) http://bit.ly/2HLuB1S https://www.teknova.com/resource/lb-m...

Its recipe is really simple and sufficient for lots of bacteria. There are 3 main components (though 2 of those components themselves have a lot of components.
- TRYPTONE:  this is a mix of peptides formed by the digesting a protein called casein with pancreatic enzyme - this provides amino acids the bacteria can use to make new proteins
- YEAST EXTRACT: this “autolysate” of yeast is basically just whatever happened to be in yeast (organic compounds including vitamins, trace elements, etc.) - and if it was good enough for the yeast…
- SODIUM CHLORIDE (NaCl)(table salt) - allows for osmotic balance, transport, etc.

A few of the major LB formulations are the “Miller,” “Lennox,” & “Luria” versions & they differ in the amount of salt they have. Miller & Bertani drown the bacteria in NaCl (10g/L) whereas Lennox just uses 5g/L and Luria just 0.5g/L - such low salt recipes are good if you’re using a salt-sensitive antibiotic

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