An Overview of Biological Basics - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 78

TABLE 2.8 Some Carbon and Nitrogen Sources Utilized by the Fermentation Industry

Carbon sources Nitrogen sources

Starch waste (maize and potato) Soya meal

Molasses (cane and beet) Yeast extract

Whey Distillers solubles

n-Alkanes Cottonseed extract

Gas oil Dried blood

Sulfite waste liquor Corn steep liquor

Domestic sewage Fish solubles and meal

Cellulose waste Groundnut meal

Carbon bean

Source: G. M. Dunn in Comprehensive Biotechnology, M. Moo-Young, ed., Vol. 1, Elsevier Science, 1985.

salts, such as KH 2 PO 4 and K 2 HPO 4 are the most common phosphate salts. Glycerophos-
phates can also be used as organic phosphate sources. Phosphorus is a key element in the
regulation of cell metabolism. The phosphate level in cell growth media should be less
than 1 mmol/L for the formation of many secondary metabolites such as antibiotics.
Sulfur constitutes nearly 1% of cellular dry weight and is present in proteins and some
coenzymes. Sulfate salts such as (NH 4 ) 2 SO 4 are the most common sulfur source. Sulfur con-
taining amino acids can also be used as a sulfur source. Certain autotrophs utilize S 2 þ and S 0
as energy sources.
Potassium is a cofactor for some enzymes and is required in carbohydrate metabolism.
Cells tend to actively take up K þ and Mg 2 þ and exclude Na þ and Ca 2 þ . The most commonly
used potassium salts are K 2 HPO 4 ,KH 2 PO 4 , and K 3 PO 4 .
Magnesium is a cofactor for some enzymes and is present in cell walls and membranes.
Ribosomes specifically require Mg 2 þ ions. Magnesium is usually supplied as MgSO 4 ,

7H 2 O

or MgCl 2 .
Table 2.9 lists the eight major macronutrients and their physiological roles.

2.4.2. Micronutrients
Trace elements are essential to microbial nutrition. A lack of essential trace elements
increases the lag phase (the time from inoculation to active cell replication in batch culture)
and may decrease the specific growth rate and yield. The three major categories of micronu-
trients are discussed below.
(1) Themost widely needed trace elements are Fe, Zn, andMn. Iron (Fe) is present in ferredoxin
and cytochrome and is an important cofactor. Iron also plays a regulatory role in some
fermentation processes (e.g. iron deficiency is required for the excretion of riboflavin by
Ashbya gossypii and iron concentration regulates penicillin production by Penicillium
chrysogenum). Zinc (Zn) is a cofactor for some enzymes and also regulates some