nearly 10,000 different prokaryotic species, including both bacteria and archaea, but this number is expected to be considerably higher and not practically obtainable.
PROKARYOTE CELL DIVISION Bacteria undergo asexual reproduction through what’s called binary fission. They only grow to a fixed size before reproducing to create identical clone daughter cells at a rate of two at a time. There are some complex ways of sending off daughter cells, including the formation of fruiting bodies, the formation of hyphae, and the process of “budding”. Budding involves the cell developing a protrusion from its cell surface that ultimately breaks from the parent cell to form a daughter cell. Binary fission is the major way these bacterial cells divide. It is similar to mitosis in animal cells and plant cells but has a different purpose. When mitosis happens in eukaryotic cells, the goal is the growth of the overall organism or the replacement of old cells by newer cells. This is not the case with bacteria. They use the process of cell division in order to reproduce or to create new organisms in the population. In binary fission, the first step is copying the DNA of the organism. These are, as you remember, circular and not confined within a nucleus. There is an origin of replication— a spot on the chromosome—that is the first part that is duplicated. The two origin sites begin to move to opposite sides of the cell—a process that begins as soon as DNA replication starts. The cell will get longer over time in order to ultimately separate. Once the two chromosomes have separated, a septum forms in the middle of the elongated organism, ultimately pinching off into two identical daughter cells. As you’ll see when you study mitosis, this binary fission process is very similar to mitosis except that there is just one chromosome and there is no mitotic spindle in binary fission to act as the separation point. In addition, the separation and replication process in binary fission happens at the same time, which is not the case with mitosis. There are four phases of bacterial growth. The first phase is called the lag phase, in which the cells begin to adapt to a nutrient-rich environment. The actual period of growth is very slow in this phase. There are a lot of biomolecules being made but no real growth in the population. Next comes the logarithmic phase, also referred to as the 57
