So herein lies the question, how can you dismiss out of hand the possibility that the Ischia culture can maintain its integrity if kept healthy? Even if your first response is that the flora in Ischia had already been replaced with different flora, if this happens with whatever replaced Ischia, how do you dismiss the possibility for Ischia or other established cultures for that matter?
If you want a simple answer, then here you go.Lb SF
has the smallest genome of any lactobacilli; in fact, at the time of its draft sequencing, it had the smallest genome size of any
free-living organism. This is important, and should not be taken lightly.
We know the conditions under which Lb SF
be dominant; your "predictive model" is based upon such data. Anything outside of that range and Lb SF
falls to the fringes.
Why does it require such a specific pH range for an organism that excretes acid? Why does it only tolerate a very narrow temperature window for a mesophilic bacterium? Because those are the external selective conditions its genome evolved to. Its dominance is only assured in the sourdough matrix, and in that matrix under the conditions we humans put before it. Those conditions are represented in your predictive model.Lb SF
does not rely upon genetic safeguards to insure its survival, as it doesn't need to; as long as humans make sourdough under the same conditions we always have, it'll remain alive and kickin'. This same trend is seen across the spectrum of food-based fermentations, with lactobacilli falling into one of two categories: generalists and specialists. The specialists have small genomes and rely solely upon the external conditions commonly created by us within their specific substrate and its associated fermentative practices for their dominance; those conditions are responsible for winnowing these bacterial genomes to their miniscule sizes and, as long as those conditions are commonly practiced, then the genome will stay its current size. Specialists, then, are very particular niche dwellers; they'll die out as soon as their niche does.
Generalists, on the other hand, have much larger genomes and a greater array of genetic stress responses (e.g., Lb plantarum
). Some of these genomes are over 100 times the size of Lb SF
, and allow this generalist population to survive under a greater range of conditions than the specialists -- Lb SF
included -- can or will tolerate.
The data we know about cold-stress is specific to Lb SF
, not most lactobacilli, which have a greater set of genetic responses to up- or down-regulate accordingly to a wider array of stress conditions. So, Lb SF
will dwindle to 1% of its population at 7 days, and 0.1% at 30 days under refrigerated conditions. We know this. However, this data is specific to Lb SF
and Lb SF
only. One of the reasons I urge bakers and pizzamakers not to put their culture in the fridge (especially longer than 3 - 4 days) is because of the chance of secondary microbiota becoming dominant, ones with larger genome sizes that can tolerate more aciduric or prolonged cold conditions, etc.
There are approximately 60 species of lactobacilli generally found both in the human gastrointestinal tract as well as human food fermentations, and almost all have been recovered from sourdough fermentations. All have different metabolic requirements and thrive under various life conditions, some hardier than others under a wider set of circumstances. Think of these as micro-Bear-Gryllses, ready and willing drink their own urine at the drop of a hat.
Research has shown conclusively that in order to be dominant Lb SF
-based cultures must be fed on a daily basis when held at ambient temperatures. If not, other organisms become dominant, which is likely the case with your Ischia culture at room temperature. The culture out of the fridge had an obvious change, shifting to a culture that is more cold-tolerant (Weissella
's, as well as certain Lactobacillus
ssp. come to mind).