An Overview of Biological Basics - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 81

A medium containing glucose, (NH 4 ) 2 SO 4 ,KH 2 PO 4 , and MgCl 2 is a defined medium.
Complex media contain natural compounds whose chemical composition is not exactly
known. A medium containing yeast extracts, peptone, molasses, or corn steep liquor is
a complex medium. A complex medium usually can provide the necessary growth factors,
vitamins, hormones, and trace elements, often resulting in higher cell yields, compared to
the defined medium. Often, complex media are less expensive than defined media. The
primary advantage of defined media is that the results are more reproducible and the oper-
ator has better control of the fermentation. Further, recovery and purification of a product is
often easier and cheaper in defined media. Table 2.10 summarizes typical defined and
complex media.

2.5. SUMMARY

Cells are the basic unit of living organisms. Living organisms can be single celled
(unicellular) or multicellular. Therefore, living organisms are commonly cellular. The
exception to the cellular living organism is a prion, which consists of protein only. Cells
are usually very small, but big ones exist and can weigh over a kilogram. There are rich
varieties of chemicals and materials associated with cells. These chemicals and materials
present opportunities for bioprocess engineers to make sustainable products that meet
the needs of humanity.
Microbes are tiny living organisms. Most microbes belong to one of the four major groups:
bacteria, viruses, fungi, or protozoa. Microbes can grow over an immense range of condi-
tions: at temperatures above boiling and below freezing; in high-salt concentrations; under
high pressures ( 1000 atm) and in strong acidic or caustic environments (pH at about

1 e 10). Cells that must use oxygen are known as aerobic. Cells that find oxygen toxic are anaer-
obic. Cells that can adapt to growth either with or without oxygen are facultative. The diversity
of the microbes provides bioprocess engineers adaptable tools to the every bioprocess condi-
tions needed.
The two major groups of cells are prokaryotic and eukaryotic. Eukaryotic cells are more
complex. The essential demarcation is the absence (in prokaryotes) or presence (in eukary-
otes) of a membrane around the chromosomal or genetic material. The prokaryotes can be
further divided into two groups: the eubacteria and the archaebacteria. The archaebacteria are
a group of ancient organisms; subdivisions include methanogens (methane-producing
organisms), halobacteria (which live in high-salt environments), and thermoacidophiles
(which grow best under conditions of high temperature and high acidity). Most eubacteria
can be separated into gram-positive and gram-negative cells. Gram-positive cells have both
an inner membrane and strong cell wall. Gram-negative cells have an inner membrane and
an outer membrane. The outer membrane is supported by cell wall material but is less
rigid than in gram-positive cells. The cyanobacteria (blue-green algae) are photosynthetic
prokaryotes classified as a subdivision of the eubacteria. The eukaryotes contain both
unicellular and multicellular organisms. The fungi and yeasts, most algae species, and
the protozoa are all examples of unicellular eukaryotes. Plants and animals are multicel-
lular eukaryotes.

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