Growth requirements of bacteria& growth curve L. Dalia Kamal Eldien MSc in Microbiology Lecture NO: 4

Questions for revision the previous lecture What the different between bacteria& blue green algae? Name the types of bacteria according to morphological classification Write the principle of Gram stain What the different between Gram positive& Gram negative cell wall?

Outlines At the end of this lecture, the student should know:- Factors affect bacterial growth Bacterial growth curve Cultivation of bacteria Theory of bacteria growth& multiplication

Introduction All cells must accomplish certain metabolic tasks to grow and divide. Bacteria need physical & chemical factors to grow

Factors affect bacterial growth (Growth Requirements) Nutrition Temperature Oxygen Carbon dioxide Moisture and drying Light pH Osmotic pressure

Nutrition factors All bacteria have three major nutritional needs for growth: A source of carbon (for making cellular constituents). Carbon represents 50% of the dry weight of a bacterium. A source of nitrogen (for making proteins). Nitrogen makes up 14% of the dry weight. A source of energy (adenosine triphosphate [ATP], for performing cellular functions). Smaller amounts of molecules, such as phosphate for nucleic acids and phospholipids of cell membranes and sulfur for protein synthesis, make up an additional 4% of the weight.

Nutrition factors Various metals and ions for enzymatic activity must also be present. Important mineral ions, such as Na+, K+, Cl−, and Ca2+, are also required. Although the basic building blocks required for growth are the same for all cells, bacteria vary widely in their ability to use different sources of these molecules

Nutrition factors Bacteria are classified into two basic groups according to how they meet their nutritional needs. Autotrophs , are able to grow simply, using carbon dioxide as the sole source of carbon, with only water and inorganic salts required in addition. Heterotrophs, requires more complex substances for growth. These bacteria require an organic source of carbon, such as glucose, and obtain energy by oxidizing or fermenting organic substances. Autotrophs occur in environment, while all bacteria that inhabit the human body are heterotrophic

Temperature Generally, an increase in temperature will increase enzyme activity. But if temperatures get too high, enzyme activity will diminish and the protein will denature. Lowering temperature will decrease enzyme activity. At freezing temperatures enzyme activity can stop Every bacterial species has specific growth temperature of its enzymes: Minimum growth temperature Optimum growth temperature Maximum growth temperature

Temperature Bacteria can be classified on the basis of temperature Thermophilic: high-temperature-loving microorganism, with growth optimum growth temperature above45°C Mesophilic: a microorganism, that lives at moderate temperature grow best at 30-37°C temperatures - many pathogens fall in this category. Psychrophilic: Cold-temperature-loving, tolerant microorganism, optimum growth temperature blew20°C

Oxygen Differences in the effect of oxygen on bacterial growth provide a further way of classifying bacteria: Obligate aerobes:- Bacteria which require free oxygen to grow Obligate anaerobes: Bacteria which are unable to grow in free oxygen

Oxygen factor 3. Facultative anaerobes:- Bacteria which can grow in conditions in which oxygen is present or absent 4. Microaerophilic:- Bacteria which grow best in conditions of reduced oxygen concentration.

Carbon dioxide factor All bacteria require small amounts of carbon dioxide for growth. This requirement is usually met by the carbon dioxide present in the atmosphere. Some bacteria like Brucella abortus require much higher levels of carbon dioxide, known as carboxyphilic

Moisture& drying factor Water is an essential ingredient of bacterial protoplasm and hence drying is lethal to cells. The effect of drying varies in different species.

pH Some bacteria grow at acidic PH (3-6), known as: acidophilic. Or grow at alkaline PH (8-10), known as: alkelophilic /basophilic. Most bacteria grow at neutral PH (7)

Osmotic pressure Bacteria vary in their tolerance to salt levels Some cannot tolerate high concentration of salt Some tolerate medium concentration of salt. Some can tolerate high concentration of salt, called: halophilic.

Growth& multiplication of bacteria Bacteria reproduce by binary fission and cell divides to form two daughter cells. Nuclear division precedes cell division and therefore, in a growing population, many cells having two nuclear bodies can be seen. Bacterial growth may be considered as two levels, increase in the size of individual cells and increase in number of cells.

Binary fission

Bacterial growth curve No growth will occur without the presence of at least one viable cell When bacteria is grown in a suitable broth medium and incubated its growth follows a definite process. After inoculation and plotted in relation to time, a growth curve is obtained.

Broth media

Growth curve The curve shows the following phase :- Lag phase: adaptation of bacteria to environment Log phase: microorganisms are growing and dividing at the maximal rate Stationary phase: number of new equal to number of death Decline phase: In this phase there is progressive death of cells

Bacterial curve

Identify the different phases A, B, C& D in bacterial growth curve

Cultivation of bacteria The purpose of using cultural techniques in microbiology is to demonstrate the presence of organisms which may be causing disease, and when indicated, to test the susceptibility of pathogens to antimicrobial agents. Thus, development of synthetic culture media and culture techniques have played important roles in the advancement of this field. Microbiologists use bacterial culture media for many purposes and applications. Culture media can be solid or broth (fluid) or semi solid

Broth media

Solid culture media

How to culture bacteria in the lab

How to culture bacteria in the lab

Bacteria grow on media plate

Bacteria grow on media plate

Sources District Laboratory Practice in Tropical Countries, Part 2 (chapter 7) Lippincott's Illustrated Reviews: Microbiology, 3rd Edition (2012)- Richard A. Harvey- Bruce D. Fisher- Richard A. Harvey-(chapter6)