Microbial Interaction

1. Commensalism
Dr. P. Suganya
Assistant Professor
Department of Biotechnology
Sri Kaliswari College (Autonomous)

2. Definition
 Commensalism is a type of ecological interaction
between two or more species where one of the
species is benefitted without either harming or
benefitting the other.
 Commensalism is a positive interaction but is quite
different interactions like mutualism or parasitism.
 It is usually a long term relationship where some
species remain in the interaction for their entire life.
 The interaction mostly exists between a larger host
and a smaller commensal. The organisms that
provide the benefit but are unaffected is the host and
the organism which is benefitted from the interaction
is the commensal.
 The commensal might even demonstrate different
forms of structural and functional adaptation based
on the relationship.

3.  The term commensalism is derived from the
term ‘commensal’ which means eating at the
same table. The term was popularized in
ecology by Pierre-Joseph van Beneden in
1876.
 The benefits obtained by the commensal
from the interaction can either be services
like transportation, protection, or resources
like nutrients.
 Commensalism, like most ecological
interaction, has played essential roles in
evolution as the interactions and adaptations
accumulate over time.
 This form of interaction can exist between the
organisms of the same species or different
species.

5. Types of Commensalism
 Commensalism is of different types
depending on the strength and duration of the
interaction and the purposes.
1. Inquilinism
 Inquilinism is a type of commensalism where
one of the species uses the body or a cavity
with the body of the other organisms as a
living.
 In this form of commensalism, one of the
species is benefitted as it attains shelter while
the other species remain unaffected.
 Inquilinism exhibits resource commensalism
where the commensal attains a resource in
the form of shelter.

6. Example- Scarab beetles and
flies
 Scarab beetles roll balls of dung which they then
bury underground in burrows as a food source
for their immatures. When they roll the ball, small
flies are attracted to the dung.
 The adult flies lay their eggs in the ball and
escape from the burrow before the beetles seal
the holes.
 The fly larvae in the ball share the dung with the
beetles’ larvae without negatively impacting the
host.
 The larvae beetles then develop into adult
beetles and dig out of the burrow while releasing
the adult flies.
 Thus, the species exist in a commensal
relationship for a short period of time, and the
interaction is essential for the lifecycle of the

8. 2. Metabiosis
 Metabiosis is a form of commensalism
where the host species unintentionally
creates a suitable environment for the
commensal.
 In metabiosis, most commensal use the
remains of some part of the remains of
the host for their benefit.
 The commensal might use the remains
of the host as tools for their survival or as
a form of protection.
 The host species involved in this form of
interaction are usually large, whereas the
commensals are small.

9. Example- Hermit crabs and
gastropod shell
 Hermit crabs live inside the empty gastropod
shell to protect their soft abdominal exoskeleton.
 The shell protects the animals against predation,
desiccation, thermal and osmotic stress. Hermits
continuously evolve to rapidly access good
quality shells through competitive interactions
with other individuals and aggregation.
 Some of the hermit crabs also carry the shells
around with them as portable homes which also
protect the organisms against predation and
other conditions.
 The ability of hermit crabs to utilize gastropod
shells as a form of living space is due to the
availability of different shapes and sizes of shells.

11. 3. Phoresy
 Phoresy is a form of interaction between two species
where the commensal or phoront latches onto the host
animals for dispersal without inducing parasitism.
 The term phoresy is derived from the Greek word ‘phorein’
meaning ‘to carry’.
 In a typical interaction, the phoront or phoretic organisms
is an animal usually a nematode or mite, with the ability to
travel limit distances and thus, requires aid in dispersal
with the help of a mobile host.
 The benefit obtained by the phoront is measured in terms
of dispersal instead of nutritional benefits, like in the case
of parasitism.
 Phoresy is a temporary interaction that continues only until
the phoront reaches the desired distance. The interaction
can, however, turn parasitic over time.
 Phoretic interactions exist between species of the entire
animal kingdom and thus are extremely diverse.

12. Example-
Caenorhabditis remanei (soil
nematode) and molluscs
 Caenorhabditis remanei is a soil nematode
that has a limited dispersal ability on its own
due to the small size and sensitivity to
desiccation.
 The species thus depends on other animals
like slugs, snails, and isopods for dispersal to
longer distances.
 The interactions are strictly used for dispersal
and to avoid harsh environmental conditions.
 Most of the species remain on the body of the
slugs, but in some cases, the organisms can
be found within the intestine of the slugs.

14. 4. Microbiota
 Microbiota is a group of microorganisms that exist
in a commensal interaction with the host surface as
they colonize a particular tissue surface.
 The system formed is termed normal microbiota,
and it mostly comprises bacteria with few fungi,
protozoans, and viruses.
 These species exist in a commensal relationship
with the host species and depend on the host for
nutrition and living space.
 Even though the population of a microbiota
develops in close parallel with the host, they do not
cause harm to the host body.
 However, in some cases, in individuals with
reduced immunity and immune-compromised
conditions, these species might cause different
diseases.

15. Example- Gut microbiota in
human
 In humans, a large group of microorganisms
resides in different parts of the body, but the most
diverse and the largest population of such
organisms reside in the gut.
 These microbes exist on the surface of human
tissue and depend on the host for nutrients and
living space.
 Even though the microorganisms take up
nutrients from the digestive system, it doesn’t
cause any harm to the host unless the species is
pathogenic.
 In some cases, the species might be
opportunistic pathogens and cause diseases in
immunocompromised individuals.

17. References
 https://microbenotes.com/commensalism/
 (2008) Commensalism. In: Capinera J.L.
(eds) Encyclopedia of Entomology. Springer,
Dordrecht. https://doi.org/10.1007/978-1-
4020-6359-6_775
 White, P Signe et al. “Phoresy.” Current
biology: CB vol. 27,12 (2017): R578-R580.
doi:10.1016/j.cub.2017.03.073
 Sourakov A. (2008) Inquilines and
Cleptoparasites. In: Capinera J.L. (eds)
Encyclopedia of Entomology. Springer,
Dordrecht. https://doi.org/10.1007/978-1-
4020-6359-6_1536

18. THANK YOU