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Bacteria: Reproduction Bacteria are unicellular organisms, unisex, multiplying by binary division. In optimal conditions, a bacterium can divide in 20 min, but in adverse conditions, the reproduction can take 1 hour to 1 day. For instance, in 48 hours one bacterium can reproduce 1 million times. It is an exponential multiplication. In the first phase of bacteria growth-cycle, bacteria adapt to the medium. The second phase is an exponential growth where bacteria reproduce. Next there is a stationary phase where the reproduction stops. Finally, there is a declining phase where the bacteria die by cannibalism (they eat each other). Limiting factors that can induce stationary and declining phase are the lack of food, self-regulation by their own toxins, competition with other micro-organisms, temperature and acidity of the environment, or the presence of chemical agents such as chlorine and phenols. Influential factors in bacteria reproduction are liquid water, temperature and pH (acidity measurement). Most bacteria like to live between10 and 45 ºC, they are mesophile bacteria. But some bacteria can live under 20 ºC, they are the psychrophile bacteria. And bacteria that live above 45 ºC are called thermophile. Common bacteria multiply at pH 5.5 to 9, but acidophile bacteria are capable of multiplying at pH 1 and opposite, alcalinophile bacteria are capable of reproducing at pH 9 and above.
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