**3.2 Microfouling**

The biofilm (microfouling) is composed mainly of water, in intervals that are between 87 and 99% of the total content. The rest of the components is very variable depending on the medium in which it is studied [17]. The matrix of the biofilm is a complex formed mainly by exopolysaccharides and bacterial cells. Other compounds that can be found are macromolecules such as proteins, DNA, and various products derived from the destruction of the cell wall of bacteria [29].

### *3.2.1 Development of the biofilm*

The biofilm begins to be generated when an individual cell initially joins a surface. The ability of this cell to carry out this binding and initiate cell growth depends on factors such as temperature and pH of the medium, genetic factors that encode its motor functions and environmental sensitivity, and those that generate adhesins and other proteins [30–33]. The factors that directly affect its development depend mainly on the microbial species, although a part of these characteristics is common to numerous bacteria.

Once initial biofouling adhesion is produced, cell growth and expansion begin on the surface, forming monolayer microcolonies. At the same time, the cells modify their activity and begin the complex process of structure formation of the biofilm. The most obvious of these changes is the production of the exopolymer matrix (EPS), which will unite the whole [34]. If the conditions of the medium allow it, the biofilm will grow and spread to non-colonized areas releasing cells that will be distributed through the water in search of new surfaces to colonize.

The formation of the biofilm is a systematic process of predictable evolution, in which five phases are differentiated [35]: (1) the reversible adsorption of the bacterium to the surface, (2) the irreversible union, (3) the first maturation phase with growth and division, (4) the growth phase with production of the exopolymer, and (5) the final development of the colony with dispersion of colonizing cells (**Figure 8**).
