Planktonic or Sessile

Microorganisms that are attached to a surface are termed sessile organisms and these are most often present as a consortium or community of organisms, collectively referred to as a biofilm. Complex assemblages of various species may occur within both planktonic and sessile microbial populations. The environmental conditions largely dictate whether these microorganisms exist in a planktonic or sessile state. 

Sessile microorganisms do not attach directly to the actual surface, but rather to a thin layer of organic matter adsorbed on the surface (Fig. 10.9, Stages 1 and 2). As microbes attach to and multiply. 

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The availability of nutrients is also a crucial factor, as it may be the principle factor in determining whether the prevailing bacterial population will be planktonic or sessile. Enos and Taylor reported on how the nutrient level could affect the mode of bacterial spatial position when the environment is poor in nutri-... 

As Figure 4.9 shows, two destinies, namely, nutrient-poor bulk solution destiny and nutrient-rich bulk solution destiny, are imaginable. In nutrient-poor bulk solution destiny, what is expected to happen, in essence, is that when nutrients— food —are scarce in the bulk solution because they are sinking onto the surface, the bulk water becomes poor in nutrients. Therefore, bacteria go to find them from what has been accumulated onto the surface. This will promote biofilm formation, and the bacteria will become motionless or sessile within the biofilm thus produced. On the other hand, the second possibility is the so-called nutrient-rich bulk solution case, where there is enough food in the bulk water, and the bacteria may find it easier to remain in their planktonic state. 

Stage 6 The exposed areas of the surface are recolonised by planktonic bacteria or sessile bacteria adjacent to the exposed areas. 

This is a general name for a wide variety of corrosion processes that may be actively or passively influenced, or induced, by an even wider variety of microbiological organisms. The electrochemical reactions that occur always result in metal wastage, as with all other forms of corrosion the most active biocorrosion processes primarily involve sessile bacteria rather than planktonic bacteria, algae, or fungi. 

Microorganisms may either be freely suspended within the bulk solution (planktonic existence) or attached to a surface (sessile existence). When a material is first immersed in an aqueous solution, a thin layer of organic matter (referred to as the conditioning film) is adsorbed onto... 

The complexity of confusions about MIC does not end with the various ways of naming it or mixing it up with other corrosion phenomena while it has been stated that there is unequivocal evidence that the observable physical or biochemical characteristics of sessile bacteria are profoundly different from those of their planktonic cousins, it has also been reported that, for example, only 1% of Pseudomonas aeruginosa genes have revealed differential expression in planktonic and biofilm cells. 

It can be inferred, then, that sessile bacteria are not simply the planktonic bacteria joining the flock of the surface-attached bacteria. The sessile bacteria could by themselves be very complicated, and for sure, their impact on corrosion is a matter that will require more research. However, in addition to the possible effects that sessile bacteria (or, in fact, biofilms) can have on corrosion, one important matter about them is that when biofilms are formed, not only the genetic and... 

In recent years, it has become obvious that the biofilm mode of growth is associated with a specific expression of genes and altered growth rates. To take into consideration the adoption of characteristic biofilm phenotypes by planktonic bacteria, a modern definition of a biofilm has been given by Donlan and Costerton (2002), who described a biofilm as a microbially derived sessile community characterized by cells that are irreversibly attached to a substratum or interface or to each other, are embedded in a matrix of EPS that they have produced, and exhibit an altered phenotype with respect to growth rate and gene transcription . 

Sampling procedures can also affect the type and frequency of microbial contaminants recovered from a contaminated fuel storage tank. The collection of samples, using a fuel sampler, provides data only on the planktonic population present in the tank water bottom and the fuel/water bottom interface where floating biofilm could be sampled. This sampling provides no information on the possible large sessile population attached to the walls of the tank. In many cases the actual level of contamination present is underestimated or misrepresented. 

A sessile organism is protected from biocides by polysaccharide slime and changes in cell metabolism. Deposit control polymers or cationic biocides like quaternary ammonium may be more effective in preventing planktonic population from attaching than some biocides that may give better planktonic kill. 

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