Clostridium botulinum is the bacterium that causes botulism (a form of food poisioning). The bacterium produces a potent toxin that causes muscle paralysis by reducing the release of the neurotransmitter acetylcholine from motor neurons.  For many other bacteria, the value (from the point of view of the microbe) is clear (for example, cholera is spread by contamination of food and water with feces from infected individuals; the cholera bacterium produces a toxin that leads to massive watery diarrhea which increases the likelihood of contamination), but I don't see how this toxin helps Clostridium.

If you drop a piece of food on the floor, it is supposedly safe to eat it as long as you pick it up before 10 seconds has elapsed, because it takes that amount of time before it can be colonised by microbial life. Is there any truth in this whatsoever?

Does washing your hands in (bearably) hot water kill bacteria? Bearing in mind the hot water is only in contact with the hands for a few seconds. I appreciate the question may be irrelevant if soap removes all bacteria anyway. Is soap 100% effective? Even so, if soap wasn't available, would hot water provide an adequate substitute to ensure the hands are free of potentially harmful bacteria?

We keep foodstuffs in the fridge to reduce bacterial spoilage but are there any bacteria that thrive best at fridge temperatures? Are some foodstuffs more likely to spoil in the fridge rather than out of it because they carry such bacteria?

Peter Hunt, Teignmouth, Devon, UK

Both my kids had almost completely black teeth around age 2. It was definitely not caries. All the dentist could tell us was that it is harmless and will eventually disappear (which it did) - but which organism (bacterium?) causes these stains, and why do only some children get them?

Can bacteria die from "natural causes" i.e. do they age?

If they were not killed by anything or died by some sort of "accident", would they potentially live forever?

The other day I cooked some egg pasta in salted water and left the pot on the stove. I was away for a couple of days afterward and was surprised on return at the extent of the bacteria that had grown in the slurry at the bottom of the pot. Can anyone identify the bacteria from the photo in particular the red blooms?

Ive recently seen an advert by Dettol which sees to trying to scare people even more than their usual methods, claiming that some bacteria can survive in lava http://bit.ly/bAJm3e. I wouldn't have thought this possiable because of the extreme temperatures and preasures the molten rock would exibit on soft object, as well as the lack of a food source that they would need to live for any amount of time. So should I worry about getting the flu if i ever fall in lava?