As directly to the target site of the

living organisms when we undergo respiration process, we bring in, then exhale
thousands of bacteria. The rate at which these bacteria probably entered and
exited the system depends on the species of the bacteria. There are bacterial
species that were able to adhere tightly to your respiratory surfaces when
inhaled and remain behind to cause illnesses like pneumonia. To determine the
possibilities of these happening, we examined the external structures those
bacteria possess.


first external structure of bacteria is the pilus (plural: pili).
A pilus is a thin, rigid fiber made of protein that protrudes from
the cell surface. The primary function of pili are to attach a bacterial cell
to specific surfaces or to other cells. However, some of the biological
properties that pili exhibit are clearly seen in the machineries that produced
them, namely chaperone–usher pili, type IV pili, conjugative type IV secretion
pili and type V pili.


bacteria assemble various non-flagellar surface organelles termed ‘pili’ or
‘fimbriae’. They are group of bacterial that do not retain the crystal violet
stain used in the gram staining method of bacteria differentiation. These
bacteria are used to deliver extracellular proteins or effectors molecules into
the surrounding environment or, in some cases, directly to the target site of
the host cell.


paper reveals that infection are been transported between bacteria and host
tissues in the cell by pili mediation during infection, or between neigh­bouring
bacteria. For example, conjugative pili facilitate contact between a donor and
an acceptor bacterium, thus enabling the cell?to?cell transport of DNA, whereas
contact that is mediated through other types of pili may lead to infection,
bacterial motility, or microcolony or biofilm formation.


author described the diverse structures and functions of assembly machineries
that are involved in the biogenesis of five known types of pili in
Gram-negative bacteria. Chaperone–usher pili are ubiquitously expressed on the
surface of many Gram-negative bacterial pathogens. They are important virulence
factors that facilitate host–pathogen interactions that are crucial for the
estab­lishment and persistence of an infection, and for other key processes
such as biofilm formation. The biogenesis of chaperone–usher pili. Type 1 and P
pili are assembled from distinct pilus subunits, or ‘pilins’, that are encoded
in the fim and pap operons, respectively.


enable bacteria to adhere to host cells and other surfaces, aid in the
formation of biofilms, bac­terial aggregates and microcolonies, and are
involved in cellular invasion, electron transfer, phage and DNA uptake, and
twitching or gliding motility. Biogenesis of T4P systems are like type II
secretion systems, which translocate folded pro­teins from the periplasm of
Gram-negative bacteria into the extracellular environment. 


in Gram-negative bacteria is a process whereby a donor cell exchanges genetic
material, such as plasmids or integrative conjugative elements, with a
recipient cell after establishing initial contact through a conjugative pilus.
Conjugation is the principal means by which horizontal gene transfer during


provide a means for bacteria to interact with and sense their environment.
Although the individual sub­units that constitute a pilus and their mode of
biogenesis can be very different, several intriguing similarities exist between
unrelated pili. For example, chaperone–usher pili, T4P and type V pili all
mediate bacterial adhe­sion. 


Pili are crucial virulence factors that are expressed by many pathogenic
bacteria and are therefore important in human disease. Thus, it was established
that the crystal structures of individual compo­nents and subcomplexes have
contributed substantially to our knowledge of the biogenesis and functions of




K Hospenthal, et al, (2017). A comprehensive guide to pilus biogenesis in
Gram-negative bacteria. Macmillan. Vol.15. pp.

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