Is L cysteine-HCL solution essentially needed for the growth of anaerobic bacteria? what is the impact if we use L cysteine without HCL?
https://www.researchgate.net/post/Cysteine_vs_Cysteine-HCl - this was discussed before. Its all about solubility. If you want to prepare a separate solution and add it after autoclaving, you will probably have problems dissolving it. I have added 0.5 g/L cysteine before sterilization and it worked fine for anaerobes like Clostridium.
Here is one preparation that is used in labs:
Reducing Agent Solution: Composition per 110.0mL: L-Cysteine·HCl·H2O ..................................................................... 2.5g Na2S·9H2O.................................................................................... 2.5g Preparation of Reducing Agent Solution: Add 110.0mL of distilled/ deionized water to a 250.0mL flask. Boil under N2 gas for 1 min. Cool to room temperature. Add L-cysteine·HCl·H2O and dissolve. Adjust to pH 9 with 5N NaOH. Add washed Na2S·9H2O and dissolve. Distribute in 10.0mL volumes into tubes. Autoclave for 10 min at 15 psi pressure–121°C.
I added L-cysteine-HCl powder directly before the step where we adjusted pH by CO2 when we made an anaerobic medium.
If you used L-cysteine but not salt form, you may see the white powder when you cool your medium and lose the reducing ability.
That's the reason we chose L-cysteine-HCl instead of L-cysteine.
I also add the sodium sulfide and Titanium(III) solution as reducing agents.
L-cysteine's reducing ability is lower than sodium sulfide and Titanium(III).
Suppose you only use L-cysteine as the sole reducing agent.
In that case, you need to make sure your anaerobic technique is perfect. You may see the medium be reduced after autoclaving.
If you want more reducing agent information, this paper is good.
Plugge CM. Anoxic media design, preparation, and considerations. Methods Enzymol. 2005;397:3-16. doi: 10.1016/S0076-6879(05)97001-8. PMID: 16260282.
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