TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Bacteria: (I) comprises a variant (which has 96 % similarity to (S1) - (S4), preferably comprises a nucleic acid sequence that is identical to (S1) - (S4).Preferred Composition: The composition is in frozen form, freeze-dried form or in the form of a powder. The composition comprising (I) having variant 16S rDNA sequence (which has 96% similarity to (S1)-(S3) or (S4)), further comprises nitrite-oxidizing and/or nitrate-reducing organisms (optionally in a mineral salt solution), or heterotrophic organisms in a mineral salt and organic based solution.Preparation: No isolation details for (I) are given. WIDER DISCLOSURE - The following are disclosed:    (1) primer sets for the detection and quantification of the bacteria present in the media, where the primer sets are composed of the sequences set 1: 5'CGGAACGTATCCAGAAGA-3' (S6) and 5'-ATCTCTAGAAAATTCGCT-3' (S7), set 2: 5'-ATCGGAACGTATCTTCG-3' (S9) and 5'-CCACCTCTCRGCGGGC-3' (S10), and set 3: 5'-TCAGAAAGAAGAAAGAATCATG-3' (S11) and 5'-GTCTCCAYTAGATTCCAAG-3' (S12);    (2) use of the primers for detecting and determining quantity of (I) in a medium; and    (3) a mixture comprising a concentrated bacterial strain capable of oxidizing ammonia to nitrite, where the 16S rDNA of the bacteria has the nucleotide sequence of (S1) - (S4).    EXAMPLE - Nine clone libraries Biofarm 16 (RTM), BC5, BC5(2), R3, R7, R7BA6, R5, R17, R13 were constructed from a number of freshwater nitrifying biomasses in order to determine the identity of the ammonia oxidizer(s) responsible for oxidation of ammonia to nitrite. The clone library data showed that there were three groups of ammonia oxidizing bacteria (AOB) that exist in the low ammonia feed reactors (e.g., R3, R7). The three bacteria were represented by three AOB clone groups-AOB Type A which has an R7clone140 sequence (S1) (and a subtype A1 which has an R7clone187 sequence of (S2)), AOB Type B which has an R3clone5 sequence of (S3). A fourth clonal type was found in high ammonia feed reactors-AOB Type C which has an R3clone47 sequence of (S4). All four sequences are given in specification.