Mould will grow on almost any surface - even glass, it just needs the right environmental factors - heat, humidity and a food source - body and soap fats... sorry for being yucky, but it's true, they grow mould on glass plates in a lab, so it's not surprising to find mould on any other surface - silicone etc included. There are solutions - use a mix of oil of cloves diluted - check Shannon Lush suggests:-

If it's a hard surface use 1/4 teaspoon of Oil of Cloves per litre of water, put it in a spray bottle, lightly mist on and leave overnight and wipe off.

In grout, remove the grout, treat the area with Tea Tree Oil and vinegar and re-grout. Same for silicone.

As for Silicone and frameless glass... The problem is the different types of silicone have varying degrees of acid in them and will 'etch' the glass, causing 'fogging' between the laminated layers of laminated glass. Hence the reason for suggesting not to silicone the glass to the wall. However, as the fogging usually only comes in around 3mm to 5mm the depth of the silicone should be about that to form a proper seal. You may be able to apply the silicone - neutral cure - clear to the inside of the glass only - bit tricky and not let it get behind the glass - inside the shower itself to close the gap, alternatively, you can use a strip of aluminium to form a sealed edge - sort of defeats the purpose of frameless glass.

Good Luck,

Andrew

Building and Pest Inspections Albury Wodonga.

http://www.buildingandpestinspectionsalburywodonga.com.au/