Amino acids are not generally required by algae, although several algae species are capable of utilizing them. Species of other microorganisms are capable of utilizing all amino acids, except for yeasts, where there is no evidence of critrulline being used. It is usually the L-form of the acids that are biologically active but, unlike higher animals, some bacteria can also utilize the D-amino acids.
It should be stressed that not all species require or utilize these compounds but rather that some species have been identified that are able to utilize these compounds. Fungi require ammonia, nitrate and nitrite.
Some species of yeasts can utilize elemental sulfur and sulfate. Generally yeasts do not require or utilize sulfur containing organic compounds. Bacteria require glutathione and thio-acetic acid while yeasts require sulphonic acid amides, thioacetate, thiocarbonate, thioglycolate and glutathione.
Chemical elements and inorganic ions
Mineral nutrients required by microorganisms are species dependent but consists generally of Fe, K, Mg, Mn. Sometimes S, N, Ca, Co, Cu, P, Zn is required.
2.5. Fermentor systems
A microbial fermentation can be viewed as a three-phase system, involving liquid-solid, gas-solid, and gas-liquid reactions.
The liquid phase contains dissolved nutrients, dissolved substrates and dissolved metabolites.
The solid phase consists of individual cells, pellets, insoluble substrates, or precipitated metabolic products.
The gaseous phase