1. Bacterial cell Amjad Khan Afridi Lecturer, Abasyn University Peshawar, Pakistan Amjad Khan Afridi Lecturer, Abasyn University Peshawar, Pakistan

2. What are Bacteria?  Bacteria are microscopic, unicellular, prokaryotic organisms.  They do not have membrane-bound cell organelles and lack a true nucleus, hence are grouped under the domain “Prokaryota” together with Archae.nucleus  Reproduce by simple division, i.e. binary fission.  In a three-domain system, Bacteria is the largest domain. (Living beings are classified into Archae, Bacteria, and Eukaryota domain in the three-domain system).  Bacteria, a singular bacterium, is derived from the Ancient Greek word “backērion” meaning “cane”, as the first bacteria observed were bacilli.  The study of ‘Bacteria’ is called ‘Bacteriology’; a branch of ‘Microbiology’.

3. Evolution of Bacteria  Bacteria are considered as the first life-form to arise on the Earth about 4 billion years ago.  A hyperthermophile of about 2.5 – 3.2 billion years ago was the ancestor of bacteria and archaea that are found in the present time.  Endosymbiotic association between different bacteria around 1.6 – 2.0 billion years ago give rise to the first proto-eukaryotic cell, which gradually gives rise to eukaryotes.

4. Ecology (Habitat) of Bacteria  Bacteria are evolved to adapt and survive in any kind of ecological niches; from normal to extreme environments. Hence, they are ubiquitous. extreme environments  They are found in every possible habitat on the Earth; soil, air, and water.  They are associated with all the biotic and abiotic components of the Earth.  They are essential components of every ecosystem.

5. Ecology (Habitat) of Bacteria  They are not only in normal ecological habitats but are also found in extreme environments.  Such bacteria are called extremophilic bacteria.  They are found in extreme cold (Psychrophiles),  Extremely hot (thermophiles),  Extreme ph (acidophiles and alkaliphiles),  Extreme pressure (barophiles),  Anoxic environments (anaerobic),  Desertic area (xerophiles), high radiation area, toxic wastes, barren sand and rocks, deep underground and mountain tip, etc.

6. Ecology (Habitat) of Bacteria  Soil is the most heavily habituated place where they found.  One gram of topsoil may contain as many as one billion bacterial cells.  It is estimated that there are approximately 2×10 30 bacteria on the Earth, but only around 2% of them are fully studied to date. Hence, there is a huge research gap on the diversity and ecology of many unknown bacterial species.  Wide varieties of bacteria live in the body of all living beings, including higher plants, animals, and even the human body.  In an average human body (normal), there are about 10 14 bacterial cells, while the body itself is made up of only 10 13 human cells.

7. Structure of a Bacterial Cell  Bacteria are unicellular i.e. made up of a single cell.  They are prokaryotes and their cells are different from animal and plant cells.  In general, the structure of bacteria can be studied as external and internal structures;

8. External Structure of a Bacteria 1. Flagella (sing. Flagellum)  Flagella are long hair-like filamentous structures of about 4 – 5 μm long and 0.01 – 0.03 μm in diameter.  They confer motility to the bacteria.  Flagella are divided into three parts; filament, hook, and the basal body.  It is made up of flagellin protein. Functions of Flagella  Responsible for motility  Chemotaxis  Bacterial pathogenicity and survival

9. 2. Pili/Fimbriae  They are the short, hollow, non-helical filamentous structure of about 0.5 μm in length and 0.01 μm in diameter. They are exclusively found in Gram-Negative bacteria.  They are composed of protein ‘pilin’ arranged non-helically. They are short, numerous, and straight than flagella.  Sex pili are a special kind of pili that take part in bacterial conjugation. They are larger than usual pili; 10-20 μm in length. They are few in number, just 1-4 in number. They are further classified into two types; F-pili and I-pili. Functions of Flagella  Aids in adherence to host cells  Sex pili helps in bacterial DNA transfer during bacterial conjugation External Structure of a Bacteria

10. Cell Wall  The cell wall is the layer that lies just outside the plasma membrane.  It is 10-25 nm thick, strong and relatively rigid, tough with some elasticity.  It is openly porous, being freely permeable.  Marks the difference between gram +ve and gram – ve bacteria

11. Functions of Cell Wall  To impart shape and rigidity to the cell.  It supports the weak cytoplasmic membrane against the high internal osmotic pressure of the protoplasm.  Maintains the characteristics shape of the bacterium.  It takes part in cell division.  Provide specific protein and carbohydrates receptors for the attachment of some bacterial viruses.  Also functions in interaction (e.g adhesion) with other bacteria and with mammalian cells.

12. Difference Between Cell Wall of Gram- positive and Gram-negative Bcateria

14. Gram-positive Bacterial Cell Wall  It is about 80 nm thick and is composed mostly of several layers of peptidoglycan.  Components of gram positve bacterial cell wall. 1.Peptidoglycan – It constitutes 50-90 percent of the dry  weight of the wall and are thicker and stronger than those of gram negative bacteria.  2. Teichoic acid – the cell wall of gram positive bacteria contain teichoic acids, which consists primarily of an alcohol (such as glycerol or sorbitol) and phosphate.

17. Gram-negative Cell Wall It is different from that of gram- positive cell wall. It consists of peptidoglycan, lipoprotein, outer membrane, 1.Peptidoglycan layer It constitutes 5-10 percent of the dry weight of the wall of gram negative bacteria. It is bonded to lipoproteins covalently in the outer membrane and plasma membrane and is in the periplasmic, gel like fluid between the outer membrane and plasma membrane.

18. 2. Lipoprotein Lipoprotein or murein lipoprotein seemingly attachto the peptidoglycan by their protein portion and to the outer membrane by their lipid component. It helps to stabilize the outer membrane and anchor it to the peptidoglycan layer. 3. Outer membrane External to the peptidoglycan, and attached to it by lipoproteins is the outer membrane. It is bilayered structure. It helps as protective barrier which prevent the entry of salts, antibiotics and other toxic substances. Outer membrane also consists of porins or transmembrane proteins whichhelps in transportation of nutrition's to the cell.

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21. Structure of Bacteria

22. 1. Cell membrane/Plasma membrane  It is the innermost phospholipid bilayer, just beneath the cell wall, enclosing cytoplasm. It is a thin (~ 5 -10 nm) semipermeable layer.  Unlike eukaryotic plasma membrane, they lack sterols (except in Mycoplasma), and comparatively have a higher proportion of proteins. In place of sterols, they have sterol-like compounds, called ‘hopanoids’.  They contain a wide variety of fatty acids like usual saturated and unsaturated types and additionally methyl, hydroxyl, or cyclic groups too.  The plasma membrane is equipped with several porin proteins for the passive transport of nutrients and ions. Functions of Cell membrane/Plasma membrane Selective permeability regulates the inflow and outflow of nutrients, ions, and metabolites Electron transport and oxidative phosphorylation Internal Structure of Bacteria It includes the cell membrane and all the structures inside the cell membrane.

23. Shape of Bacteria Cocci: cocci are spherical or nearly spherical. Bacilli: Bacilli are relatively straight, cylindrical cells. In some of the bacilli, the length of the cells may be equal to width, such bacillary forms are known as coccobacilli Vibrions : Vibrions are curved or comma shaped rods Spirillas: spirilla are rigid or helical forms Spirochetes : spirochetes are flexuous spiral forms. Mycoplasm: Mycoplasma are cell wall deficient bacteria and hence do not possess a stable morphology.

24. Arrangement of bacterial cells Pathogenic bacterial species appear as sphere (cocci), rods (bacilli), spirals. Bacteria sometimes show characteristic cellular arrangement or grouping. The type of cellular arrangement is determined by the plane through which binary fission takes place by the tendency of the daughter cells to remain attached even after division.

25. Cocci arrangment 1.Diplococci: cocci may be arranged in pairs when cocci divide and remain together. Eg. Pnemococci, Gonococci 2.Long chains: long chains when cells adhere after repeatd divisions in one plane. Eg. Streptococcus, Enterococcus, Lactococcus 3.Grape like clusters: when cocci divide in random planes. Eg. Staphylococcus 4.Tetrads: square groups of four cells when cocci divide in two planes. Eg. Micrococcus 5.Cubical packets: cubical packets of eight cells when cocci divide in three planes. Eg. Sarcina

26. Bacilli arrangement Bacilli split only across their short axes, therefore the patterns formed by them are limited. 1.Chains : Eg. Streptobacilli 2.Others are arranged at various angles to each others, resembling the letter V presenting a cuneiform or Chinese letter. Eg. Cornybacterium diptheriae

27. 1. Spherical- Cocci:  Cocci can be single or multiple in a group of 2, 4, 8, etc.  Cocci bacteria can be round, oval or elongated or bean-shaped.  The cell wall of coccus shaped bacteria may be gram-positive with thick peptidoglycan layer, or gram-negative with the thin peptidoglycan cell wall.  The cells do not separate after cell division. According to the arrangement of cells, cocci bacteria are subdivided into various subtypes:

28. Monococcus: bacteria exist as a single spherical cell Diplococcus: Cells are arranged in pairs after cell division. Examples of diplococcus bacteria are: Gram-negative bacteria- Neisseria spp, Moraxella catarrhalis Gram- positive bacteria- Streptococcus pneumoniae, Enterococcus spp, etc. Streptococcus: The cocci are joined in a plane and arranged in a chain pattern. These are non-motile, aerobic and gram-positive bacteria that cause many diseases. Examples of streptococci are Streptococcus mutans, Streptococcus pyogenes, Streptococcus bovis, Streptococcus agalactiae, etc. Tetrads: Tetrads are arranged in a group of 4 cells. The cell division occurs in two different planes. Examples of tetrads cocci bacteria are Micrococcus spp, Pediococcus, etc. Staphylococcus: Cells are arranged in an irregular cluster, which looks like grapes. This is due to the division in three planes. Examples of staphylococcus are staphylococcus aureus, Staphylococcus haemolyticus, etc. Sarcinae: Sarcinae bacteria are anaerobic gram-positive bacteria. They occur as a group of 8 cells. It is found in the family Clostridiaceae. It is found in the large intestine and skin. Examples of sarcinae are: Clostridium maximum, Sarcina auranatica, Sarcina ventriculi, Clostridium maximum, Microcioccus luteus, etc

29. 1.Spherical-------Cocci: Arrangement of Cocci Cocci/ Monococcus Diplococci Staphylococci Sarcina Streptococci Tetrad

30. 2. Rod-Shaped - Bacilli  These are rod shaped bacteria. They also occur singly or as multiple cells attached after the cell division.  Bacilli form bacteria are found in many different groups.  Bacilli form bacteria can be gram-positive, e.g. Actinomyces, Clostridium, Bacillus or gram-negative bacteria, e.g. Escherichia, Klebsiella, Salmonella, Streptobacillus, etc. Based on the arrangement of rod shaped cells, bacilli are classified into various types:

31. Bacillus: Single unattached cell, that looks like a rod. Examples are Bacillus cereus, Salmonella enterica, etc. Diplobacilli: Two rods are attached to each other and found in pairs after cell division. Examples are Moraxella bovis, Klebsiella rhinoscleromatis, etc. Streptobacilli: Due to cell division in one plane, bacilli are arranged in a chain. Genus Streptobacillus contains gram-negative, aerobic or facultative anaerobic bacteria.Examples are Streptobacillus moniliformis, Streptobacillus felis, etc. Coccobacilli: These are short compared to other bacilli and oval in shape, they appear like a coccus.Examples are Chlamydia trachomatis, Haemophilus influenzae, Gardnerella vaginalis, etc. Palisades: The bacilli after cell division bend and therefore arranged in a palisade, fence-like structure. Example: Corynebacterium diptheria

32. 1.2. Rod-Shaped – Bacilli Arrangement of Bacilli Coccobacillus Bacilli Diplobacilli Streptobacilli Palisades

33. 3. Spiral Bacteria  These bacteria are spiral or helical in shape.  Based on the thickness, flexibility and motility of the cell, they are further divided into two types:  Spirillum: These are gram-negative, rigid bacteria having external flagella. Examples are Spirillum, Campylobacter jejuni, Helicobacter pylori, etc.  Spirochete: These bacteria are spiral, thin and flexible. They have internal periplasmic flagella. These are pathogenic species that cause various serious diseases. Examples are Leptospira, Treponema pallidum, etc. These are curved and appear like a comma.  These are mostly gram-negative bacteria  They are known to cause various foodborne diseases  Vibrio sp are facultative anaerobes and have 2 chromosomes which replicate independently  Examples are Vibrio cholerae, Vibrio parahaemolyticus, etc.

34. Other than the main 4 shapes, the bacterial cell possess various different morphology namely Filamentous: Have a long filamentous structure. Example: Candidatus savagella Star-shaped: resemble a star. Example: Stella humosa, Stella vacuolata Rectangular: These are box or rectangular shaped. Example: halophilic bacteria such as Haloarcula vallismortis Pleomorphic: These have ability to change their shape and size due to various external factors like pressure, environmental stress, etc. Example: Mycoplasma pneumonia, Mycoplasma genitalium Appendaged: They are also known as budding bacteria. They can be non-motile or motile with flagella. Example: Hypomicrobium, Rhodomicrobium Trichome: Trichomes are a chain of vegetative cell. This is often covered with slimy sheath as in cyanobacteria. Example: Thiothrix nivea Lobed: These have a lobed structure and mostly found in hot and volcanic springs. They are flagellated and have an irregular shape. They are acidophiles and thermophiles. Example: Sulfolobus acidocaldarius, Sulfolobus solfataricus Fusiform: These are spindle-shaped, bulged in the middle and the end is tapered. Example: Fusobacterium necrophorum Stalked: a stalk develops at one end of bacteria due to asymmetrical cell division. Example: Caulobacter crescentus Sheathed: Bacteria cell is covered with sheath. They are found in water. Example: Leptothrix, Clonothrix

37. Thanks 27 th October, 2022