2.7 BACTERIAL CELL CULTURE
As with animal cells, pure bacterial cultures (cultures that contain only one species
of organism) are cultivated routinely and maintained indefinitely using standard
sterile techniques that are now well defined. However, since bacterial cells exhibit a
much wider degree of diversity in terms of both their nutritional and environmental
requirements, conditions for their cultivation are diverse and the precise requirements
highly dependent on the species being cultivated. Outlined below are general proced-
ures and precautions adopted in bacterial cell culture.2.7.1 Safety considerations for bacterial cell culture
Culture of microbial cells, like that involving cells of animal origin, requires care
and sterile techniques, not least of all to prevent accidental contamination of pure
cultures with other organisms. More importantly, utmost care should be given towards
protecting the operator, especially from potentially harmful organisms. Aseptic tech-
niques and safety conditions described for animal cell culture should be adopted at
all times. Additionally, instruments used during the culturing procedures should be
sterilised before and after use by heating in a Bunsen burner flame. Moreover, to avoid
spread of bacteria, areas of work must be decontaminated after use using germicidal
sprays and/or ultraviolet radiation. This is to prevent airborne bacteria from spreading
rapidly. In line with these precautions, all materials used in microbial cell culture work
must be disposed of appropriately; for instance, autoclaving of all plastics and tissue
culture waste before disposal is usually essential.2.7.2 Nutritional requirements of bacteria
The growth of bacteria requires much simpler conditions than those described for animal
cells. However, due to their diversity, the composition of the medium used may be
variable and largely determined by the nutritional classification of the organisms to be
cultured. These generally fall into two main categories classified as eitherautotrophs
(self-feeding organisms that synthesise food in the form of sugars using light energy
from the sun) orheterotrophs(non-self-feeding organisms that derive chemical energy
by breaking down organic molecules consumed). These in turn are subgrouped into
chemo-orphotoautotrophsor heterotrophs. Both chemo- and photoautotrophs rely on
carbon dioxide as a source of carbon but derive energy from completely different sources,
with the chemoautotrophs utilising inorganic substances whilst the photoautotrophs use
light. Chemoheterotrophs and photoheterotrophs both use organic compounds as the
main source of carbon with the photoheterotrophs using light for energy and the chemo
subgroup getting their energy from the metabolism of organic substances.2.7.3 Culture media for bacterial cell culture
Several different types of medium are used to culture bacteria and these can be
categorised as either complex or defined. The former usually consist of natural68 Cell culture techniques