That is an interesting finding. Microorganisms seem able to adapt to almost anything, from very high temperatures, like Thermophilus, to jet fuel (Ps. fluorescens), and now to ionizing radiation.
Background: Cladosporium sphaerospermum is one of the most common fungi seen as contaminants in cultures. It is very widespread and weakly pathogenic (disease causing). It belongs to a group called the dematiaceous fungi. That name derives from the pigment they make.
Although the finding is novel, the implication could be serious. (I didn't read the full scientific release.) The fungus may be able to derive energy from the radiation, but as pointed out in the article, it does not destroy the radio-isotopes. In other words, it doesn't change the physics. Fungi produce spores, which spread easily and far in the air. That explains why they are found virtually everywhere and are such common contaminants in laboratory cultures. Now, if the fungus incorporates the radio-isotope as part of deriving energy from the radiation, you would expect its spores to do so likewise, and that would lead to spread of the radioactive products. John