This document discusses homeostasis in bacteria. It begins by defining homeostasis as self-regulating processes that allow living organisms to maintain internal stability. It then describes several key homeostatic processes in bacteria, including iron homeostasis, metal homeostasis excluding iron, pH homeostasis, and membrane lipid homeostasis. Iron homeostasis involves specialized proteins that help bacteria absorb and store iron at optimal levels. Bacteria also regulate levels of other metals and can tolerate a wide range of pH through homeostatic mechanisms. Finally, the document presents diagrams depicting microbial interactions that maintain community homeostasis and how sugar consumption can disrupt this balance.

1. Homeostasis- Microbial ecology
Saajida Sultaana Mahusook

2. • Physiologist Walter Cannon coined the term "homeostasis" in the 1920s,
expanding on previous work by late physiologist Claude Bernard.
• In the 1870s, Bernard described how complex organisms must maintain
balance in their internal environment, or "milieu intérieur," in order to lead
a "free and independent life" in the world beyond.
• Cannon honed the concept, and introduced homeostasis to popular
audiences through his book, "The Wisdom of the Body" (The British
Medical Journal, 1932).
• Homeostasis refers to self-regulating processes that living organisms use to
maintain their internal stability, thus guaranteeing their survival.
• Bacteria can also self-regulate, adjusting to the ever changing environmental
conditions that surround them.
• The main homeostatic processes that guarantee the survival of bacteria
include iron and metal homeostasis, pH homeostasis and membrane lipid
homeostasis.

3. Iron Homeostasis
• Iron is vital to most bacteria, but in high quantities can be toxic. Bacteria can
achieve iron homeostasis even in environments with low quantities of this
element.
• In this situation, some bacteria use specialized proteins, which maximize the
absorption of iron.
• Pathogenic bacteria living in the human blood can maintain their iron
homeostasis by using the host's haemoglobin or other iron-complexes.
• Bacteria also have proteins, such as ferritine, which they used to store iron as
an intracellular reserve.
• Example: Production of siderophores- iron chelating agents by microorganisms
• When in environments with toxic levels of iron, bacteria use their iron
detoxification proteins (Dps), which protect their chromosome from damage.

4. Metal Homeostasis
• Bacteria can sense the external levels of other elements, such as
lead, cadmium and mercury.
• Metal sensors are complex proteins found in some bacteria, which
can sense and regulate the internal levels of both toxic heavy metals
and beneficial metal ions.
• The human pathogen Mycobacterium tuberculosis and the soil
dwelling Streptomyces coelicolor have more than ten metal sensors.
PH Homeostasis
• The level of acidity of a substance is measured through its pH.
• Although most bacteria species require external pH levels near
neutral or 7, bacteria called extremophiles can live in environments
with pH values below 3, or acidic, or above 11, or alkali.
• Bacteria have mechanisms for sensing external changes in pH.
• The complex pH homeostasis of most bacteria enable them to
tolerate external pH values that are different to their internal levels
of acidity.

5. Membrane Lipid Homeostasis
• The membrane of bacteria contains different types of proteins and lipids.
• Bacteria can adjust the lipid composition of their membranes, thus altering their
permeability.
• The ability of bacteria to control the lipid constitution of their membranes is
called membrane lipid homeostasis and allows them to survive in a great range
of environments.

6. A schematic diagram describes microbial–microbial interactions and their roles in
maintaining the homeostasis in a community.

7. A schematic diagram describes an example of an ecological factor, frequent consumption of sugar
(fermentable carbohydrates), to tip the balance of the community.
In the human oral cavity, frequent consumption of dietary sugar is a powerful ecological factor that can
cause population shifts and tip the balance of a dental biofilm community. Sugar favours the overgrowth of
sugar-fermentable and acid-resistant bacteria such as Streptococcus mutans (black circles) and
Lactobacillus sp. (black ovals) in dental biofilms. This will result in population shifts characterized by
dominance of S. mutans and Lactobacillus sp., but reduction or elimination of acid-sensitive bacteria
(blank shapes) in the community, leading to the homeostasis breakdown and predisposing the site to dental
caries. In this case, fewer species remain in the imbalanced community.

8. • https://www.livescience.com/65938-homeostasis.html
• Zinni, Yasmin. "What Is Bacteria
Homeostasis?" sciencing.com,
https://sciencing.com/bacteria-homeostasis-
8706627.html. 20 August 2020.
• https://www.intechopen.com/books/microbial-biofilms-
importance-and-applications/microbial-interactions-in-
biofilms-impacts-on-homeostasis-and-pathogenesis
THANK YOU