Low iron levels is a common symptoms for ME/CFS. I recently came across a study on how to improve it with the use specific probiotics.
- The Effect of Lactobacillus plantarum 299v on Iron Status and Physical Performance in Female Iron-Deficient Athletes: A Randomized Controlled Trial  Lp299v, together with 20 mg of iron, could result in a more substantial and rapid improvement in iron status and improved vigor compared to 20 mg of iron alone.
- Freeze-dried Lactobacillus plantarum 299v increases iron absorption in young females-Double isotope sequential single-blind studies in menstruating women 
- A Systematic Review and Meta-Analysis on the Effects of Probiotic Species on Iron Absorption and Iron Status  cites
- L. plantarum 299v increases iron
- L. casei increases iron
- L. acidophilus decreases iron
- L. reuteri no impact
- B. lactis no impact
Probiotics can increase or decrease iron. Our knowledge is limited. If increasing iron is critical then avoid any probiotic containing L.acidophilus. Make sure that you are taking L. plantarum 299v and L. casei