A floc is a type of microbial aggregate that may be contrasted with
biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
s and granules, or else considered a specialized type of biofilm.
Flocs appear as cloudy suspensions of cells floating in water, rather than attached to and growing on a surface like most biofilms. The floc typically is held together by a matrix of
extracellular polymeric substance (EPS), which may contain variable amounts of
polysaccharide,
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
, and other biopolymers. The formation and the properties of flocs may affect the performance of industrial water treatment
bioreactor
A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances ...
s such as
activated sludge
The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It uses air (or oxygen) and microorganism ...
systems where the flocs form a ''sludge blanket''.
Floc formation may benefit the constituent microorganisms in a number of ways, including protection from pH stress,
resistance to predation, manipulation of microenvironments, and facilitation of mutualistic relationships in mixed microbial communities.
In general, the mechanisms by which
flocculating microbial aggregates hold together are poorly understood. However, work on the activated sludge bacterium
Zoogloea resiniphila has shown that
PEP-CTERM proteins must be expressed for flocs to form; in their absence, growth is planktonic, even though exopolysaccharide is produced.
See also
*
Yeast flocculation#Process
References
Bacteriology
Biological matter
Environmental microbiology
Microbiology terms
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