**3.2 Extracellular matrix**

*Pathogenic Bacteria*

**3.1 Properties**

**3. Stages in the formation of biofilm**

make a system in which minerals can stream.

or to a unique network of biofilm [6, 7] (**Figure 2**).

There are three stages in biofilm formation: initial attachment events, the development of complex biofilms, and separation events by clumps of microorganisms or by a "swarming" phenomenon within the interior of bacterial clusters, bringing about the so-called "seeding dispersal." Once a biofilm has fully formed, it frequently contains diverts in which supplements can flow. Cells in various locales of a biofilm additionally display diverse examples of gene expression. Since biofilms regularly build up their very own metabolism, they are in some cases contrasted with the tissues of higher creatures, in which firmly packed cells cooperate and

The biofilm life cycle is observed in three different stages: attachment, growth of colonies (advancement, and occasional detachment of planktonic cells: Freedrifting, or planktonic microorganisms experience an immersed surface and then within few minutes, they can become attached. They start producing slimy EPS and eventually begin to colonize the surface [1–4]. The formation of EPS allows the biofilm network to develop a three-dimensional and complex structure which is affected by various environmental factors. These complex networks of biofilm structures can be formed within few hours [5]. Biofilms have the sections of cluster of small or large portions of cells. It can also be observed by the process of "seeding dispersal" which helps to discharge the cells which are in singular property. Both the types of cellular separation allow the microbes to get connected either to a surface

Biofilms are mostly found on the solid substrates which are either submerged in or exposed in an aqueous environment. They are present in these environments apart from the fact that they can function as floating mats on liquid surfaces and also on the external surface of the leaves, which are present especially in the

**6**

**Figure 2.**

*Stages of biofilm development [8].*

The EPS matrix is made up of exopolysaccharides, nucleic acids, and proteins. A major proportion of the EPS is somewhat hydrophilic along the hydrophobic portion. The example of such combination is cellulose which is made by many microbes. This matrix encloses the bacterial cells at intervals and also provides them the ability to communicate with each other through the biochemical signals and more importantly through gene exchange. The EPS matrix facilitates to trap the extracellular enzymes and then encloses them near the cells. This process shows that the EPS matrix has the ability of external digestion and it leads to the process of stable synergistic between various microbial species. There are some biofilms which have water channels. These water channels help them in the distribution of food and nutrients along with the signaling molecules [11].

Bacteria having the property of biofilm production are different from those which are free-floating bacterium of the same species. This is because of the dense and guarded setting of the biofilm which permits them to stick together [12]. The biofilm gives the microbe the advantage of resistance to different chemicals such as detergents and antibiotics. Thus, the dense matrix along with the external layer of cells provides a shield to the internal environment of the cells. In some instances, the biofilms increase the resistance several folds in the microbes [13]. It also helps in the lateral gene transfer in the normal microorganisms and the archaeal biofilms. This eventually makes a more stable biofilm structure [14]. But in some cases the biofilms have no contribution in the antimicrobial resistance. This can be seen in *Pseudomonas aeruginosa* which has no increased resistance to any antimicrobials as compared to the stationary-phase microbial cells which do not produce the biofilms. The biofilm production is seen in high rate in microbial cells present in the logarithmic phase of life cycle. This antimicrobial resistance seen in both the cells of the stationary phase and those of the biofilms may be contributed by the presence of persisted cells [15].

## **3.3 Quorum sensing**

The role of quorum sensing in the regulation of biofilm has been first reported by Davies which initiated the dynamic research in the cell-to-cell signaling in biofilms [16, 17]. He demonstrated that lasI-mutant cells of *P. aeruginosa* that were unfit to blend the QS signaling molecule [3OC12-HSL (3-oxododecanoylhomoserine lactone)] created undifferentiated biofilm architecture and are additionally delicate to biocide SDS. Supplementation of lasI- mutant cells with 3OC12-HSL brought about a design similar to the wild sort biofilms. The procedure of cell-to-cell correspondence in bacterial populace is known to happen through small diffusible signaling molecules perceived as autoinducer. These signal molecules are created by the bacterial cells, and their concentration in the environment relies upon the density of the population. At the point when a limit focus is achieved, the signal can initiate other microbes leading to the induction or restraint of certain target genes [18].

Cell density-dependent gene regulation phenomenon is otherwise called quorum sensing (QS). The chemical properties of signaling molecules associated with QS are differing; however gram-negative microbes most regularly utilize N-acylhomoserine lactones (AHLs). For instance, types of *Acidithiobacillus*, *Acinetobacter*, *Aeromonas*, *Agrobacterium*, *Brucella*, *Burkholderia*, *Erwinia*, *Enterobacter*, *Chromobacterium*, *Hafnia*, *Mesorhizobium*, *Methylobacter*, *Paracoccus*, *Pseudomonas*, *Ralstonia*, *Rhodobacter*, *Rhizobium*, *Rhanella*, *Serratia*, *Sinorhizobium*, *Vibrio*, and *Yersinia Williams* are referred to utilize AHLs as their major signaling molecules. In the biofilm arrangement as well as in the dispersal, QS assumes a noteworthy job. In *Rhodobactersphaeroides* (mutant cells), the addition of 7,8-cis-tetradecenoyl-HSL to the cell total brought about cell scattering prompting the development of free individual cells in suspension (**Figure 3**).
