Natural inocula contain psychrophiles
and make the digestion feasible at low temperature.
The properties that characterized and distinguished cold adapted enzymes from enzymes of higher temperature origin are their increased turnover number ([k.sub.cat]) and inherent catalytic efficiency ([k.sub.cat]/[K.sub.m]) at low temperatures, which is considered to be an adaptive strategy of the psychrophiles to compensate for low metabolic fluxes and slow reaction rates at their physiological temperatures .
Deming, "Psychrophiles and polar regions," Current Opinion in Microbiology, vol.
Nucleotide and protein sequences of [beta]-galactosidase of thermophiles, mesophiles, and psychrophiles were retrieved from NCBI (http://www.ncbi.nlm .nih.gov/) and UniProt proteomic server (http://www.uniprot.org/), respectively.
Blastp (Protein BLAST) (http://blast.ncbi.nlm .nih.gov/) was performed to study the homology among the various [beta]-galactosidase sequences and six sequences each belonging to thermophiles, mesophiles, and psychrophiles were selected (Table 1).
Dataset was divided into three groups, that is, thermophiles, mesophiles, and psychrophiles, according to their optimum temperature for [beta]-galactosidase activity.
Aromatic and basic amino acid increased in percentage as we go from psychrophiles to thermophiles.
Arginine and proline were slightly higher in [beta]-galactosidase of psychrophiles and thermophiles whereas mesophiles have marginally higher percentage of asparagine and glutamic acid.
The largest number of species overall was found in the area near the embayment, including many that are common to freshwater environments, as well as marine species, psychrophiles
 found psychrophiles
isolated from minced freshwater fish even when incubated at 0[degrees]C.
Many of the prokaryotes isolated from high temperature environments are obligate thermophiles, whereas those resident in low temperature environments are not obligate psychrophiles
and generally grow optimally at much higher temperatures (Knoll and Bauld 1989).
Over the last years, extremophiles with its different categories, thermophiles (high temperature), acidophiles (low pH), alkaliphiles (high pH), halophiles (high salinity), and psychrophiles
(low temperature) , have fascinated researchers in many fields, due to their ability to withstand and function under extreme conditions.