Planktonic versus sessile life of prokaryotes

Abstract

Because of the extremely small size of most prokaryotic organisms, the limits on what is meant by the terms planktonic and sessile require definition. According to the Oxford English Dictionary, planktonic refers to drifting or floating organic life found at various depths in the ocean or fresh water. At the micrometer level, a planktonic habitat for prokaryotes can also encompass water films around soil particles, saliva in the mouth, fluids in the intestinal lumen, serum in blood vessels, and urine in the bladder and urinary tract. Sessile, on the other hand, means immediately attached, without a footstalk. Again, one can extend this definition to include those prokaryotes directly adhering to surfaces, those attaching by means of a holdfast at the end of a prostheca (e.g., Caulobacter), those embedded in biofilms developing as a result of extracellular polymer production by bacteria colonizing surfaces, and those colonizing mucus excreted by higher organisms (as in the gastrointestinal tract and the mucigel of plant roots).