Identifying Characteristics of Yeast, Mold, Protozoa and Rickettsia


Yeast are group of non-mycelial unicellular fungi belonging to the group Ascomycetes. They are cosmopolitian fungi which occur in almost all places of the world having organic matter, especially sugars. Most of the species are saprophytes. They grow on the nectar of flowers, surface of sweet fruits, sugarcane, milk and other food stuffs, animal excreta, humus of soil etc.

In general, yeast cells are longer than most bacteria. Yeast vary considerably in size ranging from one to five μm in width and from 5 to 30 μm or more in length. They are commonly egg shaped but are sometimes lemon shaped, pear shaped or elongated into false or true mycelium. Yeast have no flagella and other organelles of locomotion. Read more

Bacterial Structures Internal to Cell Wall and Reproduction

The bacterial structures internal to cell wall includes cytoplasmic membrane, protoplast, spheroplast, spores, plasmid and others.

Fig: Structure of bacteria ( uploads/2015/ 02/B9780323069380000062_gr2.jpg )

Cytoplasmic membrane: This is a thin structure that completely surrounds the cell. Its size is approximately 7.5 nm in thickness and is composed primarily of phospholipid (20 – 30 %), protein (60 – 70 %). The phospholipid form bilayered structure in which most of the protein are embedded tightly called integral protein. This protein can only be removed by destruction of the membrane with treatment such as with detergent. Other protein which are loosely attached are called peripheral protein. This peripheral protein can be easily removed mild treatment such as osmotic shock. Read more

Morphology of Bacteria and its Structures External to Cell Wall

The morphology of bacterial cell includes characteristics such as size, shape, structure etc. First of all, Leeuwenhoek revealed the gross appearance of microorganism including bacteria by light microscope. By the discovery of electron microscope in early 1940’s the study of structural bacterial cell has been made very easier. The morphological characteristic of a bacterial cell is as follows.

Size: Bacteria vary in size from cell to cell. It can be as small as 0.1 to 0.2 μm in width to as large as more than 50 μm in diameter. A few very large prokaryotes such as Epulopiscium fishelsoni [1] that inhabits the intestinal tract of Surgeon fish  are up to 50 μm in diameter and can be more than 0.5 mm in length. However, the dimension of an average rod cell prokaryotes E.coli are about 1×3 μm. Read more

Preservation and Maintenance of Industrially Important Cultures

Microorganism for the production of industrially important products are useful only if they can be maintained indefinitely in healthy, pure and genetically stable form. Industrial culture collection consists of stock culture. Stock culture may be simply defined as a culture which serves as source of inoculum. Stock cultures are of two types.
1. Working stock culture: Working stock culture: This culture is maintained at vigorous and uncontaminated condition. Since this culture is used frequently, it must be routinely checked for characteristic feature and contamination.
2. Primary stock culture: This culture is kept for long term storage and are maintained at low physiological activity condition. The cultures are used to produce new working stock culture as per need. Read more

Single Cell Protein (SCP)

Fig: Single Cell protein ( .com/ site/mehdidastgheib/scp2.jpg)

Microbial protein are commonly called single cell protein (SCP) referring to the fact that most of the microorganism used as protein producers are single cells or filamentous individual. SCP is a generic name which refers to dry cells or protein concentrates from microorganism obtained by growing in large amount in variety of abundant and inexpensive culture media and used as protein supplement for human and animal. SCP should not be confused with biomass (ex; mushroom) and microbial biomass. SCP can be produced using different species of bacteria, yeast or fungi.

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Culture and Culture Media

Pure culture: A culture that contains only one kind of microorganism is called a pure culture. A culture which contains more than one kind of microorganism is called a mixed culture. A pure culture has only a single type of colony. Pure cultures are essential in order to study colony characteristics, biochemical properties, morphology, staining reaction, immunological reaction or susceptibility towards antimicrobial agents of particular strain of fungus, bacteria or actinomyces. Read more

Microscopy and Types of Microscopes

Microscope is an optical instrument consisting of lens for making enlarged or magnified images of minute objects. Robert Hook (1635 – 1703) made and used a first compound microscope. The basic difference between simple and compound microscope is that simple microscope uses only one lens whereas, compound microscope uses more than one lenses to further magnify the object.

Fig: compound microscope

The ability of microscope to distinguish two adjacent object as separate and distinct images rather than single blurred image is called resolving power of microscope. Theoretically, size of image can be increased by adding lenses. Magnification of object is only useful if the enlarged image is clearly visible. So, effective magnification depends on resolving power of microscope.

A microscope’s resolving power is dependent on wavelength of beam for illumination and optical quality of lenses. Shorter wavelength gives better resolution. Resolution or shortest distance (d) can be calculated by using the formula, d = λ/2nsinϴ  where, d = resolution, λ = wavelength of light, n = refractive index and ϴ = angle subtended.

Note: Oil is used with oil immersion lenses because it has higher numerical aperture than air and also higher refractive index and this greatly improves resolution. Read more