Major Groups Of Microorgenism And Their Characterstics

MAJOR GROUPS OF MICROBES

MICROBES

The term microbe is short for microorganism which means small  organism – observed with a microscope

Over 99% of microbes contribute to the quality of human life

A small minority cause disease – in humans by sheer numbers or  producing powerful toxins

The major groups of microbes are Archaea bacteria, , algae, fungi,  protozoa & viruses

In terms of numbers, microbes represent most of the diversity of life

on Earth and are found in every environment.

MAJOR GROUPS

PRIONS – acellular

General Characteristics – ultramicroscopic proteinaceous infectious particles

Importance – associated with a number of diseases characterized by loss of motor control, dementia,  paralysis, wasting and eventually death

VIRUSES – acellular

General Characteristics

·Are acellular

·Consists of a piece of nucleic acid (DNA or RNA) encased in protein and in some cases a  membrane-like envelope

·They come in many shapes

·Are parasites – found anywhere there are cells to infest

·Are small – ranging from 20 – 400 nm

·Exist to reproduce – must take over a suitable host cell

·Uses the cell machinery of the host cell to reproduce

Mode of Transportation – outside of a living cell a viral particle is inactive

Mode of Reproduction – viruses must infest a living cell and use the cellular machinery of the infested  cell in order to reproduce. The genetic material can mutate.

Importance of Viruses

Phage typing of bacteria to help identify bacteria during disease outbreaks

Source of enzymes

Pesticides

Anti-bacterial agents

Anti-cancer agents

Gene vectors for protein production and treatment of genetic disorders

Serve as the infecting agent for a number of diseases

ARCHAEA – prokaryotic  General Characteristics

Are typically smaller than eukaryotic cells

Similar to bacteria in many characteristics including size and shape –  Can have some unusual shapes

Found in a variety of shapes: coccus, bacillus, spirillium, plate-like and  can cluster together: diplo, strepto, staphylo

Unlike bacteria – Cell walls lack peptidoglycan plus other

SEM ~ 5 mcm long

differences in the chemical composition of many of their structures.

Origin very old – have been on the planet for billions of years back to the formation of the earth

Respond to light (phototaxis), food (chemotaxis), temperature (thermotaxis), and to each other  (conjugation)

Some species are extremophiles living in extremes of salinity, temperature, and pH and being  extremely tolerant to heat, acid, and toxic gases

May be found in a variety of terrestrial and aquatic environments

Not known to cause disease

Mode of Movement – move using flagella made of flagellin also have intracellular movement

Modes of Nutrition- photoautotrophic, chemo-autotrophic, photo-heterotrophic and chemo-heterotrophic

Mode of Reproduction – reproduce by cell division: known as binary fission involving one genomic  chromosome and replicons…but not by mitosis. They grow very rapidly, dividing every 20 minutes,  doubling in both size and number recombination can be achieved by conjugation

BACTERIA – prokaryotic

General Characteristics

Consist of only one cell – a prokaryotic cell

Live in all environments – even above boiling point  and below freezing point

Are typically smaller than eukaryotic cells

Are basically three shapes – spherical , rod, and  spiral or helical

Exist as individuals or cluster together to form pairs,  chains, squares, or other groupings

Some are photoautotrophic – make their own food  as plants and give off oxygen

Some are chemoautotrophic – synthesize their own  food using energy from chemical reactions – important for recycling in nitrogen and sulfur cycles.

Some types are also aerobic – use oxygen for respiration while others are anaerobic

Some form spores which allow them to survive severe environmental conditions

Bacterial spores can exist at extreme environments for centuries.

Mode of Transportation – Some have flagella – rotates like a tiny outboard motor, others secrete a slime  layer and move over surfaces like slugs, while others are immobile.

Mode of Reproduction – grow to a fixed size then reproduce through binary fission, a form of asexual  reproduction, resulting in the formation of two bacterial cells that are genetically identical.

GRAM + AND GRAM BACTERIA

Gram positive bacteria

Stain purple under Gram stain

Have a thick bilayer wall of the polymer peptidoglycan.

Gram negative bacteria Stain red

Have a thin layer of this polymer and an additional  lipopolysaccharide outer layer, LPS, often endotoxic – capable of initiating inflammation and  cell-mediated immune responses e.g., Salmonella, Shigella, and Escherichia.

BACTERIAL SHAPES

Bacillus is rod-shaped

coccus is ball-shaped

spirilium is spiral-shaped

vibrio is comma-shaped

cocco-bacillus is ovoid-shaped

other combinations

ALGAL PROTISTS (ALGAE) – eukaryotic

General Characteristics

Plant-like occurring as single cells, thread-like filaments, or colonies of various shapes and composition

Cells, like those of fungi, are surrounded by rigid cell walls.

Most cell walls made of polysaccharide (cellulose or agar), but some contain quantities of glass (silica dioxide) as with diatoms

Found in fresh and salt water environments

Can live on rocks, trees, and in soils with enough moisture

Some types live inside other organisms

Photoautotrophs and contain chlorophylls

Can carry on photosynthesis – produce large amount of oxygen  for life on earth

They are self-feeding (autotrophic) and as producers provide food for  other organisms

Spirogyra

Examples are Diatoms, Volvox, Clamydomonas , Spirogyra

Mode of Transportation – some types of algae have flagellated forms

Mode of Reproduction

Both sexually and asexually, with asexual reproduction occurring more commonly

Algae, like fungi, produce asexual spores of various types.

ANIMAL-LIKE PROTISTS (PROTOZOA) – Eukaryotic

General Characteristics

Protozoa means “little animal” – act like tiny animals – Eukaryotic

Vary greatly in shape and size

Size varies from 10 to 50 mcm but some are as large as 1000  mcm

Most prefer a pH near normal (pH of 7)

Unicellular eukaryotic microorganisms lacking a cell wall

Some have cells surrounded by hard shells

Most have a single nucleus

Some have both a macronucleus and one or more micronuclei.

Contractile vacuoles may be present to remove excess water

Heterotrophic – hunt other microbes for food

Food vacuoles are often observed – obtain large food particles  by phagocytosis

Mainly feed on bacteria, also other protozoa and some algae

Digest food in digestive organelles

Some protozoa as Euglena have chlorophyll and can photosynthesize·Most are found in moist environments as freshwater, salt water and soil

Most species are aerobic but a few anaerobic species are found in human intestines  and animal rumen

Mode of Transportation – Most can move independently

They are organized by mode of transportation

Ciliates – hair-like cilia (Paramecium)

Amoebaes – foot-like pseudpods (Amoeba)

Flagellates – whip-like flagella (Euglena)

Mode of Reproduction

They can reproduce by binary fission or multiple fission. Some produce sexually.

Still others reproduce using a combination of both. Some types alternate between a free-living vegetative form known as a trophozoite and a resting form called a cyst. The protozoan cyst is like the bacterial spore can resists harsh conditions  in the environment. Many protozoan parasites are taken into the body in the cyst form. In the trophozoite stage, they feed actively

FUNGI – eukaryotic

General Characteristics

Single celled as yeast or multicellular clusters as molds & mushrooms

Cellular level, more like animals than plants

Cell walls contain chitin

Heterotrophic – can’t synthesize their own food – secrete digestive enzymes  into surrounding environment to break down large organic molecules to  simple molecules that they can absorb

Most are aerobic, some are facultative anaerobic (ex. yeast) and some are anaerobic

Can’t tolerate high temperatures but some types can tolerate high sugar concentration, high acid  environments, and extremely cold temperatures

Grow best under conditions that are somewhat acidic – often prefer pH of 5

Multicellular ones form filament like strands – hyphae

Cross walls between fungal cells called septa and some species lack these septa as bread mold

Grow best in slightly acidic environment – can grow in low moisture

Live in soil, on plants & animals, in fresh & salt water

One teaspoon of topsoil has about 120,000 fungi.

Mode of Transportation

Non- mobile

Mode of Reproduction

Sexual and asexual modes of reproduction

Form sexual and asexual spores

Yeast form buds for asexual reproduction