I’m going to be honest, it was mostly just looking at things that already exist.
So, my pitch for why heavy metals would be useful is this:
Remove environmental toxin clouds as toxins that would be found normally, and replace them with a catch all heavy metal. If you wanted to keep the random land mines of doom around, well, there is a reasonable solution for why something toxic would exist (heavy metals are found in the world, and do inhibit protein function). Then, once a player has ran into/died from it, leave it as an opening for a simple toxin. It would be an interesting playstyle, actually: you don’t produce your own toxins, but find them naturally. From there, you could give the option to branch out into other toxins (this is just my pitch, but it provides a straightforward way for players to deal with an enviromental hazard, and an opening for more interesting toxin play that isn’t the current idea of die a bunch → get toxins). Just an idea though.
On to more ideas for extremophile organelle upgrades:
Hydrogenosomes: Found in low oxygen environments, these nifty little guys produce ATP from glucose without requiring oxygen. Less efficient, but useful when in anaerobic environments. Also produces hydrogen, and is often the basis for methane production. Useful when you want to make your organism produce flammable gasses for whatever reason.
Alkili-dependent gradients: Found in Alkaliphile bacteria, this set of proteins makes use of the massive inverse gradient found when attempting to produce ATP in an extremely basic environment to vastly increase the efficiency of production. In practice: This would have a lower base ATP production than standard, while becoming far more efficient as the alkilinity of the surrounding environment increases. Could also be used to minorly shift the optimal PH for a bacteria. (We’re still not quite sure how the bacteria manages to make an inverse gradient work as well as they do, but somehow they manage it.)
While there isn’t any good counterpart I know of on the Acidphile microorganisms, acids are commonly found in areas with heavy metal concentration (look up acid mine drainage), so I offer this:
Acid Dependent gradients: Given at extremely low PH values, iron can actually have a higher oxidization rate than oxygen, these proteins would be far more efficient in areas such as undersea vents (where the PH can be as low as 3). More or less as above, see this as a version that is more efficient in the vents where it would normally be found. (I would actually argue that this would be the starting Rusticytene, where the protein under highly acidic conditions evolved to use the more efficient electron donor). See Ferroplasma for roughly what I’m thinking of.
Acid Independent: This would be a side evolution, removing the acid dependency for iron eaters, leaving it more or less how it’s set up now. (If the above suggestion is taken, this would be the evolution someone leaving the vents would take to keep ATP production up, possibly unlocked once you actually leave the vents? If not, I’m personally fine with leaving the specialist as just an upgrade, it’s just a little closer to LAWK if it follows that path, and gives a straightforward upgrade path.)
Now for a new Vacuole upgrade:
The “Oh Belgum Button”: A near surface vacuole that when activated causes the microbe to forcefully expel it’s contents. While in the beginning this would just be water, it could be applied to toxin vacuoles (or their equivalent). More or less, this would be an option for everyone looking for jet propulsion. I’d personally expect a fairly long cooldown (you would have to reform the vacuole in it’s entirety) and be somewhat energy intensive, but would be interesting both as a predator (fast lunges anyone) as well as prey (have some mild paralytic toxin if you want to follow me). While there isn’t anything I can think of that uses this method off the top of my head, it would be interesting.
Psuedopod: Rather than having the Pili do damage in and of itself, this would increase the range that engulfment could be achieved at. Think of it less as “there’s a psudopod here” and more along the lines of “I tend to use psuedopods”. Basically, just trying to get some love for engulfers, because right now it can be hard to catch the little annoyances that are bacteria. Don’t run, I just want to eat you! Not sure if you want this to be incompatable with cell walls, ect, or it there could be a niche for this (tanky with a glaring weak spot?).
Increased cellular machinery/double bound nucleus: Since gogi bodies and endoplasmic reticulum are currently all wrapped up in the nucleus, this would be an upgrade to the nucleus that increases the amount of these that would be found in the cell. While this could have variable effects, it would be interesting to see this as a way to gain access to another protein, representing the cell’s increased ability to fold and package proteins, and allows some granularity: An early nucleus wouldn’t provide a lot of slots, and then once you upgrade it you get access to the full breadth. (This is mostly just from the feeling that dropping a whole nucleus is expensive → offering a - still very expensive - intermediary makes it still feel like you’ve achieved something, but gives that wiggle room that if you need just a little bit more to stay ATP positive you could drop one more metablisome if the idea that copies are cheaper to add holds true.) If not, then maybe just the option to trade mutation points for an extra slot.
Micronucleosis: If the above option doesn’t work, then wrapping everything under the banner of microncucleosis and instead trading ATP (and some mutation points) for the extra slot(s). (I tried to see what the final decision on how micronucleosis was to be treated, but I couldn’t find anything in the dev forums besides that it was not going to offer more mutation points/reduce mutation slots, so this is attempting to give a use for it.)
Question, are cell walls, ect on the menu for possible upgrades? It might be interesting as you start to transition towards multicellular to create an exocellular matrix as an upgrade to binding proteins/base for bones/scales/ect (I hope I have the right terminology, been a while since I took anything close to microbiology).