[Catalytic and Stereoselective Properties of the Immobilized Amidase of Rhodococcus rhodochrous 4-1]

The amidase of Rhodococcus rhodochrous 4-1 was immobilized by covalent attachment to activated chitosan by physical sorption on carbon adsorbents and by the formation of crosslinked aggregates in the absence of carrier material. Comparative analysis of particular catalytic properties of the free and chitosan-immobilized amidase was performed. It was shown that the enzyme retained 50-60% of its initial activity after covalent immobilization on chitosan and was characterized by increased temperature stability as compared to soluble amidase. Moreover, the immobilized enzyme retained more than 20% of its activity after five 24-h cycles of acrylamide deamination. The effects of different types of immobilization on amidase stereose-lective properties were studied by the model reaction of racemic lactamide hydrolysis to D-lactic acid and L-lactic acid. It was shown that crosslinked amidase aggregates possessed high D-stereoselectivity (up to 77-94%). The immobilized enzyme showed the highest enantioselectivity at 60 degrees C.

[Activated Sludge Bacteria Transforming Cyanopyridines and Amides of Pyridinecarboxylic Acids]

Species diversity of bacteria from the activated sludge of Perm biological waste treatment facilities capable of transformation of cyanopyridines and amides of pyridinecarboxylic acids was investigated. Enrichment cultures in mineral media with 3-cyanopyridine as the sole carbon and nitrogen source were used to obtain 32 clones of gram-negative heterotrophic bacteria exhibiting moderate growth on solid and liquid media with 3- and 4-cyanopyridine. Sequencing of the 16S rRNA gene fragments revealed that the clones with homology of at least 99% belonged to the genera Acinetobacte, Alcaligenes, Delftia, Ochrobactrum, Pseudomonas, Stenotrophomonas, and Xanthobacter. PCR analysis showed that 13 out of 32 isolates contained the sequences (-1070 bp) homologous to the nitrilase genes reported previously in Alcaligenes faecalis JM3 (GenBank, D13419.1). Nine clones were capable of nitrile and amide transformation in minimal salt medium. Acinetobacter sp. 11 h and Alcaligenes sp. osv transformed 3-cyanopyridine to nicotinamide, while most of the clones possessed amidase activity (0.5 to 46.3 mmol/(g h) for acetamide and 0.1 to 5.6 mmol/(g h) for nicotinamide). Nicotinamide utilization by strain A. faecalis 2 was shown to result in excretion of a secondary metabolite, which was identified as dodecyl acrylate at 91% probability.

[Transformation of amides by adherent rhodococcus cells possessing amidase activity]

We report the development of a heterogeneous biocatalyst for the hydrolysis of amides that is based on cell adhesion ofamidase-containing Rhodococci on activated birch carbon (ABC) and crude carbon. We investigated the properties of the obtained biocatalyst in the hydrolysis reaction of acrylamide to acrylic acid and nicotinamide to nicotinic acid, as well as in a model reaction of racemic lactamide hydrolysis to a mixture of D- and L-isomers of lactic acid. We show that a six- and threefold increase in the concentrations of adherent and suspended cells, respectively, results in a reduction of amidase activity by 3 and 30 times, respectively. ABC Cells adherent on ABC maintained more than 50% of enzymatic activity for seven 24-hour cycles of acrylamide hydrolysis, while suspended cells lost more than 60% of activity already in the second cycle. We also noted that cell adhesion on ABC reduced the stereoselectivity of hydrolysis reaction of racemic lactamide.

[Transformation of 2- and 4-cyanopyridines by free and immobilized cells of nitrile-hydrolyzing bacteria]

The transformation dynamics of 2- and 4-cyanopyridines by cells suspended and adsorbed on inorganic carriers has been studied in the Rhodococcus ruber gt 1 strain possessing nitrile hydratase activity and the Pseudomonas fluorescens C2 strain containing nitrilase. It was shown that both nitrile hydratase and nitrilase activities of immobilized cells against 2-cyanopyridine were 1.5-4 times lower compared to 4-cyanopyridine and 1.6-2 times lower than the activities of free cells against 2-cyanpopyridine. The possibility of obtaining isonicotinic acid during the combined conversion of 4-cyanopyridine by a mixed suspension of R. ruber gt 1 cells with a high level of nitrile hydratase activity and R. erythropolis 11-2 cells with a pronounced activity of amidase has been shown. Immobilization of Rhodococcus cells on raw coal and Pseudomonas cells on china clay was shown to yield a heterogeneous biocatalyst for the efficient transformation of cyanopyridines into respective amides and carbonic acids.

[Catalytic properties of a nitrile hydratase immobilized on activated chitosan]

The catalytic properties of a nitrile hydratase, isolated from a strain of Rhodococcus ruber gt1 and immobilized by covalent cross-linking with chitosan activated with 0.1% benzoquinone solution, have been investigated. The kinetic parameters ofacrylonitrile hydration catalyzed by immobilized nitrile hydratase and the enzyme in a solution have been determined. It is found that the immobilization does not lead to a decrease in the maximum reaction rate (Vmax), whereas the Michaelis constant (K(M)) is reduced by a factor of 2.4. The possibility of reusing an immobilized enzyme for 50 consecutive cycles of acrylonitrile transformation was shown, and the nitrile hydratase activity in the 50th cycle exceeded that in the first cycle by 3.5 times. It is shown that the effect of temperature on activity depended on the concentration of the enzyme, which confirms the dissociative nature of nitrile hydratase inactivation. It was found that immobilized nitrile hydratases remain active at pH 3.0-4.0, whereas the enzyme is inactivated in a solution under these conditions. The resulting biocatalyst can be effectively used to receive acrylamide from acrylonitrile.

[A study of the catalytic properties of the nitrile hydratase immobilized on aluminum oxides and carbon-containing adsorbents]

The nitrile hydratase isolated from Rhodococcus ruber strain gt1, displaying a high nitrile hydratase activity, was immobilized on unmodified aluminum oxides and carbon-containing adsorbents, including the carbon carrier Sibunit. The activity and operational stability of the immobilized nitrile hydratase were studied in the reaction of acrylonitrile transformation into acrylamide. It was demonstrated that an increase in the carbon content in the carrier led to an increase in the amount of adsorbed enzyme and, concurrently, to a decrease in its activity. The nitrile hydratase immobilized on Sibunit and carbon-containing aluminum alpha-oxide having a "crust" structure displayed the highest operational stability in acrylonitrile hydration. It was shown that the thermostability of adsorbed nitrile hydratase increased by one order of magnitude.

[Effect of bacterial satellites on Chlamydomonas reinhardtii growth in an algo-bacterial community]

The growth characteristics of an algo-bacterial community (Chlamydomonas reinhardtii and bacterial satellites) were studied, as well as the mechanism and patterns of bacterial effect on algae. Four strains of predominant bacteria were isolated and partially characterized. They were assigned to the following taxa: Rhodococcus terrea, Micrococcus roseus, and Bacillus spp. A pure culture of the alga under study was obtained by plating serial dilutions on agarized media with ampicillin. Within the algo-bacterial association, the alga had a higher growth rate (0.76 day(-1)) and yield (60 microg chlorophyll/ml culture) than in pure cultures (0.4 day(-1) and 10 microg chlorophyll/ml culture, respectively). The viability of the algal cells within the association was retained longer than in pure culture. Among the isolated bacterial satellites, strains B1 and Y1, assigned to the species Rhodococcus terrae, had the highest stimulatory effect on algal growth. The culture liquid of bacteria incubated under the conditions not permitting growth stimulated algal growth; the culture liquid of actively growing bacteria had an opposite effect.

[Effects of nitriles and amides on the growth and the nitrile hydratase activity of the Rhodococcus sp. strain gt1]

Effects of some nitriles and amides, as well as glucose and ammonium, on the growth and the nitrile hydratase (EC 4.2.1.84) activity of the Rhodococcus sp. strain gt1 isolated from soil were studied. The activity of nitrile hydratase mainly depended on carbon and nitrogen supply to cells. The activity of nitrile hydratase was high in the presence of glucose and ammonium at medium concentrations and decreased at concentrations of glucose more than 0.3%. Saturated unsubstituted aliphatic nitriles and amides were found to be a good source of nitrogen and carbon. However, the presence of nitriles and amides in the medium was not absolutely necessary for the expression of the activity of nitrile hydratase isolated from the Rhodococcus sp. strain gt1.