Question

Q1. What is the S-layer? How does it function and what is it's structure?

Q2. What benefits do gut microbes offer humans and what do humans offer gut microbes?

Answer 1

1) S-layer is a part of the cell covering, which is present in almost all archaea and many types of bacteria. It consists of a monomolecular layer composed of the same proteins or glycoproteins. This structure is built by self-assembly and encloses the whole cell surface. Therfore, the S-layer protein can represent up to 15% of the whole protein content of a cell. These proteins are poorly conserved or not preserved and can differ markedly even between related species. The S-layers of diverse organisms have unique structural properties, which include symmetry and unit cell dimensions, due to fundamental differences in their ingredients of building blocks. It is composed of multiple domains, which are structurally related. S-layers exhibit either an oblique, square or hexagonal and lattice symmetry. Each morphological unit of the S-layer is composed of one (p1), two (p2), three (p3), four (p4), or six (p6) identical protein subunits that depends upon the lattice symmetry. The unit cell dimensions between these subunits range from 4 to 35 nm. The S-layer denotes the outermost interaction zone with their respective surroundings in many bacteria. Its functions are very diverse and vary from species to species. In many archaeal species the S-layer is the only cell wall element and therefore, it is essential for mechanical and osmotic stabilization.

S-layers include additional functions: i) Protection against bacteriophages, Bdellovibrios, and phagocytosis.

ii) Resistance against low pH and barrier against high-molecular-weight substances.

iii) Stabilisation of the membrane and provision of adhesion sites for exoproteins

2) Gut microbes is the complex community of microorganisms, which live in the digestive tracts of humans and other animals. The relationship between some gut microbes and humans is not merely commensal, but rather a mutualistic relationship. Some human gut microorganisms benefit the host by the process of fermentation of dietary fiber into short-chain fatty acids, as acetic acid and butyric acid and after then absorbed by the host. Intestinal bacteria also play an important role in synthesizing vitamin B and vitamin K ,metabolizing bile acids, sterols, and xenobiotics. The systemic importance of the short-chain fatty acids and other compounds they produce are like hormones and the gut flora itself shows to function like an endocrine organ, and dysregulation of the gut microbes have correlated with a host of inflammatory and autoimmune situations. The composition of human gut microbes changes over time, when the diet changes, and as overall health changes.