S layer of Bacteria

Many archaea and bacteria have a proteinaceous surface layer, also known as an S-layer. It forms when monomeric proteins self-assemble into a regularly spaced, two-dimensional array. Bacteria have specific routes for secreting and anchoring the S-layer to the cell wall. Also, certain Gram-positive species have substantial S-layer-associated gene families. S-layers perform critical roles in the development and survival of the bacteria. They are involved in numerous tasks including cell integrity maintenance, and enzyme display. In pathogens and commensals, contact with the host and its immune system.

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Key Features of Bacterial S layer

• Genetic investigation revealed a diverse set of genes that encode S-layer proteins (SLPs) in different species, also mechanisms that permit gene switching and control.
• Secretion of S-layer proteins frequently requires a specific secretion system. For example, the supplementary Sec systems seen in Bacillus anthracis and Clostridium difficile, and a variety of methods for attaching S-layers to the underlying cell envelope have been discovered.
• Gram-positive organisms, such as B. anthracis and C. difficile, have vast gene families that encode proteins similar to the S-layer protein. Thus they have a common anchoring mechanism.

Genetic Analysis of S-Layer Proteins

In certain species, there is a large diversity of genes that encode S-layer proteins (SLPs), according to genetic study, and various mechanisms are discovered to help with gene regulation and switching. There are several different ways to bind S-layers to the underlying cell membrane. However, most typically, secretion of S-layer proteins occurs through a specific secretion system, such as supplementary Sec systems in Bacillus anthracis and Clostridium difficile. Gram-positive organisms have a wide gene family expressing proteins related to the S-layer protein that have a similar anchoring mechanism, such as B. anthracis and C. difficile.

• It is possible that gene duplication resulted in a family of genes with functional variety since certain firmicutes possess numerous S-layer gene homologs with differing levels of sequence similarity.
• The general makeup of S-layer proteins from different evolutionary branches is quite comparable, according to the analysis of amino acids.
• Acidic and hydrophobic amino acids are often present in high concentrations in S-layer proteins. The most common basic amino acid is lysine, with very little arginine, histidine, or methionine present.
• Cysteine was only found in a small number of S-layer proteins. Many archaea and gram-positive bacteria’s S-layer proteins can contain covalently bonded carbohydrate chains.

Gerbino, E., Carasi, P., Mobili, P., Serradell, M. A., & Gómez-Zavaglia, A. (2015). Role of S-layer proteins in bacteria. World Journal of Microbiology and Biotechnology, 31, 1877-1887.

Biological Significance of S layer of Bacteria

1. For many bacteria, the S-layer is the outermost point of contact with their surroundings. Its functions differ greatly between species. In many archaeal species, the S-layer is the only cell wall component, hence it is critical for mechanical and osmotic stability.
2. The S-layer is permeable, which helps it perform various roles including protection against bacteriophages and resistance to low pH and high molecular weight compounds. The S layer is likely to give adhesive properties to the bacteria and also provides attachment sites for exoproteins.
3. Stabilization of membrane resistance to electromagnetic stress and antifoaming properties are some other biological aspects of the S layer.

Biofilm Formation

The role of S-layer proteins in biofilms is not unprecedented. Numerous studies have implicated S-layer proteins in biofilm-related processes such as cell adhesion to substrates, promotion of cell-cell aggregation, and initial biofilm establishment. In general, interactions between the bacterial cells, the substrates, and the surrounding medium are necessary for the production of bacterial biofilms. Extracellular DNA (eDNA) was present in small amounts in the protein and carbohydrate complexes that made up the D. radiodurans biofilm matrix, according to biochemical studies. Additionally, research revealed that the addition of 25 mM Ca2+ increased the biofilm development of D. radiodurans and increased the amount of protein and exopolysaccharides in the biofilm matrix.

SLPs can disrupt immune responses in infections and promote their survival by adhering to host cells. Gram-positive bacteria frequently have roles linked to an effector domain that can bestow characteristics other than the capacity to form a two-dimensional array. Certain Gram-positive species have extensive gene families linked to the S-layer, and bacteria have specific routes for secreting and attaching the S-layer to the cell wall. S-layers perform a variety of vital tasks for development and survival, such as preserving cell integrity, displaying enzymes, and interacting with the host’s immune system in the case of infections and commensals.

REFERENCES:

1. Sleytr, U. B., Schuster, B., Egelseer, M., & Pum, D. (2014). S‐layers: Principles and applications. FEMS Microbiology Reviews, 38(5), 823-864. https://doi.org/10.1111/1574-6976.12063
2. Fagan, R. P., & Fairweather, N. F. (2014). Biogenesis and functions of bacterial S-layers. Nature Reviews Microbiology, 12(3), 211-222. https://doi.org/10.1038/nrmicro3213