THE NITROGEN CYCLES

MO regulates nitrogen reserves in soil and their accessibility to higher plants by assimilation and immobilization of nitrogen by: symbiotic and non- simiobiotic nitrogen fixation, nitrification, denitrification, ammonification as follows: ^[1]

• • Nitrates can be reduced to N, (denitrification).
• • MO from soil and water decompose the organic compounds with nitrogen, releasing it as ammonia (ammonification).

Ammonification is the process of mineralization of organic nitrogen compounds, which releases nitrogen as ammonia. Nitrogen from organic compounds, otherwise inaccessible, becomes accessible due to ammonifica- tion. Ammonification occurs with proteins, AA, nucleic acids, and nucleotides, nucleosides, purines, and pyrimidine bases, lipids, and carbohydrates containing nitrogen, creatinine, hippuric acid, urea, alkaloids, etc., (Wu et al„ 2018). Decomposition of proteins from plant, animal, and MO residues.

Several examples of proteolytic MO are as follows: proteolytic bacteria: aerobic, spomlated: Bacillus cereus var. mycoides, B. subtilis, B. megaterium, B. thennoproteoliticus; nonspomlated: Setratia marcescens, Arthrobacter; optional anaerobic: Proteus vulgaris, Pseudomonas fiuorescens; obligatory anaerobic: Clostridium putrefaciens. Proteolytic bacteria Bacillus cereus var mycoides, is the most active in the culture media, while in the soil, under natural conditions, the most active is Proteus vulgaris. Proteolytic actino- mycetes: Streptomzces violaceus, Micromonospora chalcea; Proteolytic mushrooms: Pemcillium, Aspergillus, Mucor, Rhyzopus, Alternaria.

BIOCHEMISTRY OF PROTEIN DECOMPOSITION

Biochemistry of protein decomposition has two stages: hydrolysis and deza- mination and decarboxylation of AA (Martinez-Santos et ah, 2018).

Hydrolysis is an extra and intracellular process, comprising:

• • Hydrolysis of protein towards peptides, with proteinases;
• • Hydrolysis of peptides towards AA, with peptidases.
• • Proteinases are:
• • Serine Proteinases: They have serine and histidine active in the center. They are alkaline proteinases, owing an optimal pH of 9-11. An example is the proteinase produced by Aspergillus, B. subtilis-swbtilisin. ^[2]

• • Acid Proteinases (Carboxyl-Proteinase): with optimal pH below 5, produced by Aspergillus niger, Penicillium janthinelum, Mucor pusillus.
• • Metallo-Proteinases: It contain Zn²' neutral, produced by Bacillus subtilis.
• • The peptidases are:
• • Aminopeptidases (removes only one ammo acid residue from the N terminus of the chain, e.g., Aeromonas proteolitica);
• • Carboxipeptidases (removes one amino acid from the С-terminal end of the chain, e.g., Serin carboxipeptidase-Penicillium, Aspergillus, metal carboxypeptidase).
• • Dipeptidases (hydrolyses dipeptides, e.g., Mycobacterium phlei)
• • Peptideases for dipeptides at the N-tenninus and, respectively, the C-terminus of the peptide chain (Roohi et al., 2017).

Dezamination and decarboxilation of AA is an intracellular process.

Oxidative dezamination is done with amino acid dehydrogenases + NAD or NADP coenzyme. It can also be done with amino acid-oxidases (flavin enzymes) + FAD coenzyme, with Cu or vitamin В12 enzymes. During hydrolytic dezamination the NH, group of AA is not hydrolyzed by MO. The occurrence of a-hydroxyacids is explained by the reduction of a-ketoacids formed by the oxidative deamination pathway, while the primary alcohols appear by the dehydroxylation of a-hydroxy.

Amino acid decomposition produces toxic substances:

• • Decarboxylation gives putrescine, cadaverine from ornithine;
• • Histamine is produced from histidine.
• • Tyramine, which is toxic at high doses results from tyrosine (Graves et al., 2016).

The decomposition of nucleic acids is done with ammonia release. Decomposition is by: nucleotide depolymerization, nucleotide hydrolysis with nucleoside and o-phosphate formation, hydrolysis of purine or pyrimidine base nucleosides and ribose or deoxyribose, deamination of nitrogenous bases. Decomposing MO are the following: Bacillus, Clostridium, Arthrobacter: actmomycetes: Streptomyces; fungi: Aspergillus, Penicillium, Cephalosporium, Mucor, Fusarium, etc.

DECOMPOSITION OF NITROGEN-CONTAINING LIPIDS

Cephalines and lecithins from organic residues are enzymatically hydrolyzed resulting in glycerol, fatty acid, o-phosphate, and a nitrogen compound: colamine or choline. Artrobacteria decompose choline to glycine by two successive oxidations and 3 demethylations.

DECOMPOSITION OF NITROGEN CARBOHYDRATE

Chitin, murein-inucopeptide or peptidoglucan from the cellular basal wall of eubacteria is an aminopolysaccharide. It decomposes into soil, the final products being:

У Creatinine Decomposition:

Creatinine hydrolysis —*■ creatine —> urea and sarcosine —> glycine demethylation —*■ NH₃+ 2CO, + H,0 У Urea Decomposition: The decomposition of urea is done in the soil under the action of urobacteria, actinomycetes, and fungi. In 1866, Pasteur named the decaying bacterium: Torula ammoniacale. Bacillus pasteuri and Sporosarcina ureae are alkaline pH resistant. MO decompose soil urea originating from nitrogen metabolism in mammals (mine), from some fungi, or formed during the decomposition of purine and pyrimidine bases, arginine, and creatinine, from synthetic fertilizers. Urea accumulated in the soil is decomposed to ammonia and carbonic acid.

DECOMPOSITION OF CALCIUM CYANAMIDE

Ca Cyanamide is a nitrogen-containing fertilizer containing calcium carbide.

DECOMPOSITION OF ALKALOIDS

Alkaloids originate from plant remains: coffee-caffeine, tea-tlieophylline, cocoa-theobromine. Other alkaloids are: nicotine, atropine, quinine. Soil- bome MO that are able to degrade alkaloids are bacteria: Pseudomonas putida, Ps fluorescens, Bacillus coagulans; fungi: Penicilium. Methylxan- thine is degassed by hydrolysis to methanol and xanthine-which degrades oxidatively. Other nitrogen compounds are also decomposed by soil borne MO (vitamins, antibiotics, chlorophylls, drugs, pesticides, artificial dyes) (Yanet al., 2016).

AMMONIA TRANSFORMATIONS

Abiotic transformations that occur can be described as follows: ammonia adsorbed by clay minerals neutralizes acids in the soil, volatilizes to alkaline pH and is then leached from the soil. The biotic transformations: NH₃ and ammonium salts are assimilated by MO.

NH₃ is oxidized to nitric acid and MO nitrates. Nitrification is the oxidation of ammonia to nitrites, in the soil. Denitrification is the reduction of nitrite to organic N.

The biological bonding of molecular nitrogen is run by N, fixative bacteria: Azotobacter, Azomonas, Klebsiella, Bacillus, Clostridium, Cyanobacteria. Green plants assimilate nitrogen in mineral form by transforming it into organic nitrogen. MO from soil and water decompose organic compounds with nitrogen, releasing nitrogen as ammonia. Ammonia is oxidized to nitrate under the action of nitrifying MO. Nitrates can be reduced to N, (denitrification) (Li et al., 2015).

BIODEGRADATION OF ORGANIC WASTE AND RESIDUES: THE ISSUE OF DIOXINS

Uncontrolled combustion on the platforms, even the domestic waste- incinerator, produces large amounts of dioxins and furans, which own high toxicity and which are concentrated in the environment (water, air, soil) and in trophic, aquatic, or terrestrial chains. Specialty literature from Canada, UK, Belgium, the Netherlands, the USA, etc., reported the fact that the incidence of cancer and toxic phenomena in humans and animals is significantly higher in neighboring of incinerated waste platforms.

Under these circumstances, it is necessary to reuse all the waste, no matter how much it would cost to adjust their quality for further recirculation. Agriculture, the largest consumer of organic waste, can become the user of biodegradable waste, which can provide an energy base for increased productions and environmental cleanliness. The methods of recycling waste in agriculture and related sectors are multiple: soil fertilization, energy recycling, recycling as a direct or indirect source of animal feed, etc., (Wu et al., 2015).

• [1] Green plants assimilate nitrogen in mineral form (ammonium salts,nitrates). Legumes also use N, by MO symbionts from root nodules(the symbiotic fixation of N,). • Ammonia is oxidized to nitrate under the action of nitrifying MO(nitrification).
• [2] Thiol-Proteinases: They have cysteine active center (streptococcalthiol-proteinase).