What is the difference between a spore and a cyst? Last year I read a course in biology. During that course I learnt that Protozoa like Lamblia intestinalis or Entamoeba hystolitica form _cysts_ in unfavourable conditions. This year I read a course in microbiology. I learnt that bacteria like Clostridium perfringens or Bacillus anthracis form _spores_ in unfavourable conditions. So far so good. But then I learnt that prokaryotic Borrelia burgdorferi can form a _cyst_ , not a spore. Firstly, I would highly appreciate any comments that would cast some light on these terms. Secondly, I would also like to know if the spore inside, say, B.anthracis is the same organism as B.anthracis that produced the spore. Does a spore and the bacteria that produced it have the same DNA sequence? In other words, **if I were a sporeforming bacteria, would my spore be myself, my bodypart or my child?**

The bacterial spores you are referring to are called endospores. The spore is formed during unfavorable conditions, by duplication of the bacterial chromosomes, and consequent envelopment by various membranes and protective coatings (while still within the original cell). The spore is dormant and remains so as the outer cell degrades during harsh conditions, releasing the spore. I guess I'd call the spore a clone of the original?

You may enjoy reading the relevant sections in this book, which go into greater detail.

edit: as Souvik has pointed out, this is only one type of "protective" spore. Actinomycetes also form spores, via differentiation of the cells, and cyanobacteria form akinetes also via differentiation (but this structure is not as durable as endospores).

Information about cyst formation is difficult to find, but in bacteria it appears to develop via changes in cell wall composition.