Mold (I think?) - and what I should be doing about it

[Bliz]

So we had a leak a few months ago with a few isolated water spots (and one small drip) appearing in the kitchen ceiling. The spots were about 6 inches out from the kitchen wall and 2-3 feet from each other - one a circle about 5" diameter (which had a small drip coming out of the center), one a circle about 9" diameter, and one a thin line maybe 2 feet long. The laundry room is upstairs and above part of the kitchen, so we thought it was a pipe leak and called a plumber, but he thought not and instead traced it to a damaged pipe boot which has since been repaired. Plumber didn't rip up any of the floors or anything to check the lines running to the washer.

There is no visible water damage upstairs.

Took this picture in the attic of what I think is a little bit of mold growing around where the leak was.

Can I kill it with bleach without damaging the wood?

Second, and more importantly, I'm a little worried about what might be growing in between the walls, since we assume the water must have dripped down in between the walls in order to stain the kitchen ceiling without staining or damaging anything upstairs.. Is it worth having someone out to take a look recognizing this would involve some destructive testing and general mess-making, or since the leak has been stopped, will it just dry out and take care of itself?