BACTERIA AND PROTISTS by Hafiz Wicaksono

BACTERIA:  Are prokaryotic microorganisms, found almost everywhere throughout the Earth.  Decompose organic matters, making them vital to the ecosystem.  Usually lack nuclei and membrane-bound organelles.  Can be either autotrophic or heterotrophic.  Reproduce via binary fission.

DISCOVERY Bacteria were first discovered by Dutchman Antonie van Leeuwanhoek in 1674 when he used a magnifying lens to observe some pond water and found a variety of microorganisms. He is now known as the Father of Microbiology. French scientist Louis Pasteur discovered that microorganisms are responsible for the spoiling of food. In 1862, he and Claude Bernard tested a method of slowing down bacterial growth by heating the food a certain amount and then cooling it immediately, a process now known as pasteurisation.

FORMS Bacteria have a wide range of shapes, including:  Coccus (spherical)  Bacillus (rod-like)  Spirillum (spiral), and  Filamentous

 Nucleoid: where the bacterium’s nucleic acid is concentrated.  Ribosomes: translate genetic message from messenger RNA into peptide sequences.  Flagella: used for propulsion.  Capsule: promotes adhesion to surfaces. STRUCTURE

LIFE CYCLE Bacteria reproduce by binary fission. Their growth consists of several phases:  Lag: the bacteria mature and adapt to their surrounding, producing nucleic acids, vitamins and amino acids.  Log/Exponential: the bacteria multiply rapidly.  Stationary: decrease and eventual halt in multiplication thanks to waste accumulation and depletion of nutrients.  Death: Bacteria lose reproductive ability and die en masse ~ x_x

ROLES  Bacteria break down and decompose organic materials, converting them into nutrients for the environment.  Some bacteria are pathogenic, inflicting harmful infections upon host organisms, such as Mycobacterium tuberculosis and Salmonella enterica.  Most bacteria, however, are harmless. Bacteria can be found in digestive tracts, helping to break down and digest food.  Some bacteria in the soil can convert atmospheric nitrogen into ammonia, which is in turn converted into nitrate and finally back into nitrogen gas. These bacteria are essential to terrestrial life.

PROTISTS:  Are a diverse group of eukaryotic microorganisms.  Have been traditionally divided into several groups:  Protozoa: unicellular with animal-like behaviour.  Algae: immobile and plant-like.  Slime molds: fungi-like, reproduce with spores.  Can be phototrophic or organotrophic.  Reproduce either sexually (via gametes) or asexually (via binary fission).

PROTOZOA:  Are unicellular and lack cell walls.  Alternate between two forms: trophozoite, where they absorb nutrients from a host, and cyst, where they are dormant.  Are often found in the sea as zooplanktons.  Need nutrients from outside sources to survive.  May act as pathogens.

ALGAE:  Are a diverse group of plant-like organisms that lack true stems, leaves, roots and vascular tissues.  Metabolise through phototrophy and form the basis of many food chains.  Respire oxygen, accounting for half of the Earth’s oxygen production.  Can be found in the sea as phytoplanktons.

SLIME MOLDS:  Are a broad group of protists that reproduce with spores, with their life cycles superficially resembling fungi.  Feed on decaying organic matter.  Plasmodial slime molds are enormous single cells with numerous nuclei.  Cellular slime molds are single-celled amoeboid protists that can aggregate into great swarms.

REFERENCES  University of California Museum of Paleontology Official Site  US National Library of Medicine -  About.com -  Molecular Expressions -  University of Leeds Official Site -  The Biology Corner -