**5. Phytase**

Phytases are enzymes that hydrolyze phytic acid which is an organic phosphorus source and makes inorganic usable phosphorus. Bacterially produced phytases are 3-phytase (EC 3.1.3.8), 4-phytase (EC 3.1.3.26) and protein-tyrosine-phosphatase (PTP, EC 3.1.3.48). Besides PTP, the other enzymes differentiate at which carbon they attack and take out the phosphorus in phytic acid. Several reports are available on the production of phytases. The organisms used are *Aerobacter aerogenes, B. amyloliquefaciens, B. subtilis, Enterobacter* sp., *E. coli, Klebsiella aerogenes, Lactobacillus amylovorus, Pseudomonas* sp., *Selenomonas ruminantium* [70] for three and four phytases and *B. subtilis, M. tuberculosis, S. aureus* [71–73]; typically grown under complex media (tryptone, yeast extract and NaCl and sugars, for example, lactose as inducer)

The activity of bacterially produced phytases change with pH, ranging from 2 [74] to 10 [75], while the optimum pH range is narrower (from 2.7 [76] to 8.5 [77]). As for the temperature, optimum working range is between 20 [78] and 80°C [79] due to the presence of some thermophilic organisms [70, 79]. The molecular weight range is found to be between 12.8 [80] and 700 [70] kDa, again depending on the producing host.

Similar to the other enzymes, several metal ions are reported to inhibit the phytase activity. These include Ba2+, Cd2+, Cu2+, Li+ , Mg2+, Mn2+and Zn2+ [77, 81], while EDTA is considered as an activator compound [75]

#### **6. Urease**

An important enzyme for plant nutrition, in particular for N-cycle is Urease (EC 3.5.1.5), catalysing the conversion of urea to carbon dioxide and ammonia:

$$\text{(NH}\_2\text{)}\_2\text{CO} + \text{H}\_2\text{O} \rightleftharpoons \text{CO}\_2 + 2\text{NH}\_3\tag{1}$$

This enzyme is produced by bacteria, fungi as well as plants. Some bacterial producers are listed as *A. aerogenes, Arthrobacter oxydans, Bacillus pasteurii, Brevibacterium ammoniagenes, Brucella suis, E. coli, Helicobacter pylori, Proteus mirabilis, Providencia stuartii, S. ruminantium, Sporosarcina pasteurii, Staphylococcus saprophyticus* and *Ureaplasma urealyticum* [82–84], while the following organisms are reported to produce acid urease: *Arthrobacter mobilis, Lactobacillus fermentum* and *Streptococcus mitior* [82]. These are typically grown in batch mode, under complex (yeast extract, peptone and glucose) or chemically defined medium conditions, mezophilic temperatures, with urea as the inducer of the enzyme production [85, 86].

The pH range whereby the enzyme works optimally is 2–9 [87–90], while optimum temperature ranges from 20 to 70°C [91–94]. Molecular weights can vary from 11.1 [82] to 600 [90] kDa. Listed inhibitors are methylurea, thiourea, acetohydroxamic acid, phenylphosphorodiamidate, H<sup>3</sup> PO<sup>4</sup> , 2-mercaptoethanol, boric acid, lodoacetamide, lodoacetic acid, N-Ethylmaleimide, 5,5′-Dithiobis (2-nitrobenzoic acid) (DNTB) [95]; 12-hydroxytetradecanoc acid, 3-hydroxytetradecanoc acid, 6-hydroxytetradecanoc acid [96, 97] and several metal ions [98, 99]. Glycerol, n-octylglucoside, polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), Triton X-100 have some activatory effect in certain amounts [100]. It is worth noting that urease is nickel-containing metalloenzyme, as a result of which requires to a certain level nickel metal [101], as usual higher concentrations have inhibitory effect [99].
