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I'm quite new to biology, but I'm wondering if there are any methods of storing bacteria in long-term, dry conditions with no climate control. Perhaps they could be dormant in a powder or granule-like form similar to yeast. The species that I'm trying to work with is a gram-negative bacteria called C. Metallidurans. What's pretty cool about this bacteria is its ability to survive in environments that are high in heavy metals and produce pure gold from gold chloride. Any advice helps, thank you.

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Lyophilization, aka freeze-drying, is probably the go-to method of microbial preservation without the need for cold storage. It's how bacterial strains purchased from commercial culture collections are typically shipped.

The process consists of first freezing cultures in a lyophilization buffer containing a mixture of cryoprotectant and lyoprotectant excipients, which is exposed to a strong vacuum (while maintaining sub-freezing temperatures) to sublimate the frozen water out of the mixture (source). The lyophilized powder is typically sealed in a glass ampoule filled with inert gas for long-term storage, but can also be packaged in any number of ways to for application-specific uses.

Unfortunately, there's probably not a one-size-fits-all formula that works best for every organisms, but there may be some approaches that are "good enough" for most. Under the right conditions, lyophilized cultures can be stable for years with minimal loss of viability, but I wouldn't count on it without extensive optimization and process validation. Also would not recommend it as your sole method of long-term preservation. Best practice is to always keep glycerol stock backups at -70°C or colder, and to have a plan in place for how often these stocks should be assessed/renewed.

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  • $\begingroup$ Nice answer. I'd add that it needs some specialist equipment to freeze dry under the controlled conditions needed. $\endgroup$
    – bob1
    Nov 20 at 20:18
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The answer to this strongly depends on the species of bacterium you are working with.

The only ones that I know of that are capable of withstanding any dehydration process are those that form spores. The spores are tough, long-lasting structures that enable the bacterial species to resist environmental changes.

Cupravidus metallidurans, the species you are working on is not a spore-former, so it isn't possible to fully dehydrate them. However, it is possible to form long-term stocks of many, if not all, bacterial species in glycerol and frozen at -80 C (ultra-cold freezer) sort of temperatures.

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    $\begingroup$ Most bacteria can tolerate lyophilization under controlled conditions, which essentially results in a desiccated powder. But it's a highly controlled process and the long-term stability of freeze-dried bacteria is more variable than that of frozen glycerol stocks. $\endgroup$
    – MikeyC
    Nov 20 at 16:31
  • $\begingroup$ @MikeyC true - I completely forgot about freeze drying. I was about to suggest you write it up as an answer, but then saw that you already had. $\endgroup$
    – bob1
    Nov 20 at 20:16

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