contributed by Miguel Vicente
All living creatures are born, grow, reproduce and finally die. Consequently, as many flow without discontinuity from one cell to the next (Escherichia coli in the gut), a number of them do not grow (Salmonella enterica inside some phagosomes), others fail to reproduce (Mycobacterium tuberculosis in latent infection) and, finally, some do not even die (Bacillus subtilis after sporulation) are bacteria alive?
I must disagree with Stanley. I believe that metabolism is central to "life", not the ability to reproduce. Many things that reproduce are not living, such as ideas, products on a machine line, sand crystals being eroded from a rock, or CFCs reproducing the same chemical reaction in the Ozone layer. What makes something living is its ability to "do" things, which are a result of metabolism. That being said, I do not believe viruses are living, just because they reproduce (and they can't even do it by themselves)!
Nevertheless, bacteria are living and should be considered so in your examples. To be living, one does not have to be constantly reproducing (Mtb does have the ability to reproduce at some time points), or die within a given frame (B. subtilis will eventually die in the event of a nuclear attack). Also living things do not have to continuously grow... humans stop doing so after their teens (referring to the S. enterica example)!
Great question and interesting discussion!
Posted by: Jessica Ferreyra | August 21, 2009 at 08:04 PM