We breath oxygen primarily because it's highly electronegative and hence works as an electron attractor in the electron transport chain system of atp production. This is a rather specific metabolic system and it's far from foundational, tons and tons of bacteria don't have this type of energy system, (in fact even humans have several others in addition to this one!)
In fact, there are really existing earth bacteria that use metals in their metabolic systems, and frequently absorb environmental sulfur or oxygen (or probably other things, maybe not hydrogen though, H2 is very stable) as a way of breaking down metals into more usable forms.
Really you've just got to decide how detailed you want to get with this. Fully describing the chemistry of a totally novel metabolic cycle seems like it would be pretty hard, certainly it's above my pay grade. At the same time, I wouldn't doubt for a second the plausibility of "a Bacteria which metabolizes [some metal] by absorbing [some gas] in a low oxygen atmosphere". Hell, there's probably one on Earth that fits the bill.
To fill out this response with some more specific information, you can look at a couple of the following things:
1: Sulfate Reducing Microorganisms: https://en.wikipedia.org/wiki/Sulfate-reducing_microorganisms -- these are examples of bacteria that "breath" sulfates instead of oxygen to power their respiration. In other words, they use sulfates as the final electron acceptor in their electron transport chain. 938
These are prokaryotes however. Some of these are called Chemolithoheterotrophs, which is the class of bacteria here that reduces inorganic material rather than organic material, which is kind of the thing you are looking for. 2. https://microbewiki.kenyon.edu/index.php/Dissimilatory_metal_reduction Here is a short article talking about how microbes can "consume" metals to produce energy. In your post you said you wanted the microbe to consume metals to gain mass, but keep in mind that for the most part the mass of a single microbe is naturally limited by scaling factor difference between volume (~mass) and surface area (~max "eating" rate), so for a colony of bacteria to gain mass by consuming metals you just need a metal to be "consumed" (usually this means corroded or oxidized) as part of the colony's metabolic process.
I'd hoped to find an example of a specific Earth bacteria fitting your criterion, but I wasn't able. However, nothing about what you're asking for is too 'out of this world' (yuk-yuk) certainly the individual elements you're asking for are well represented and pretty well understood. 561