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Among the compounds that contain unusual functional groups, nitro is perhaps one of the most interesting due to the valuable properties it confers on pharmaceuticals and explosives. Traditional chemistry has for many years used environmentally unfriendly strategies; in contrast, the biocatalyzed production of this type of products offers a promising alternative. The small family of enzymes formed by N-oxygenases allows the conversion of an amino group to a nitro through the sequential addition of oxygen. These enzymes also make it possible to obtain other less oxidized N-O functions, such as hydroxylamine or nitroso, present in intermediate or final products. The current substrates on which these enzymes are reported to work encompass a few aromatic molecules and sugars. The unique characteristics of N-oxygenases and the great economic value of the products that they could generate, place them in a position of very high scientific and industrial interest. The most important and best studied N-oxygenases will be presented here., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Aromatic nitro compounds are key building blocks for many industrial syntheses and are also components of explosives, drugs and pesticides. Due to the environmentally unfriendly experimental conditions involved in their chemical syntheses, industrial processes would benefit from the use of biocatalysts. Among potentially useful enzymes, N-oxygenases, whose role is to oxygenate primary amines, are becoming relevant. These enzymes are involved in different secondary metabolic pathways in Streptomyces and in few other bacteria, forming part of the enzyme pools implicated in antibiotic synthesis. In this work, a group of Streptomyces strains, whose biomass was obtained from simple and novel culture media, were identified as new sources of N-oxygenase activity. Furthermore, the use of unspecific metabolic stimulation strategies allowed substantial improvements in the activity of whole cells as biocatalysts. It is remarkable the 6 to 50-fold increase in nitro compound yields compared to the biotransformation under standard conditions when Streptomyces griseus was the biocatalyst. In addition, biocatalyst substrate acceptance was studied in order to determine the biocatalytic potential of this enzyme., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Organophosphorus compounds (OPs), the major pesticides used worldwide, comprise an environmental hazard due to their harmful toxicity. Aimed to develop a bioreactor to remediate OPs contaminated wastewater, bacteria isolated from contaminated soils were identified and their ability to degrade OPs assessed, resulting in two main isolates, Sphingomonas sp. and Brevundimonas sp. Their OP degrading activities were characterized in terms of temperature, pH and substrates acceptance, resulting in high degradation rates at 60 °C, pH 10 and towards bulky OPs such as coroxon, coumaphos, and chlorpyrifos. Sphingomonas sp. cells were immobilized and 75.4% degradation of 0.15 mM chlorpyrifos was achieved after 21 days by immobilized cells in batch system, while this OP was completely degraded within 17 h when the biocatalyst is settled in a packed bed bioreactor, with a reusability of 8 cycles. These results suggest the potential application of this system in the bioremediation of contaminated wastewater., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The biocatalyzed synthesis of purine nucleosides and their analogs is a case widely studied due to the high pharmaceutical interest of these compounds, providing the whole-cell biocatalysts, a useful tool for this purpose. Vidarabine and fludarabine are commercial examples of expensive bioactive nucleosides that can be prepared using a microbial transglycosylation approach. Citrobacter koseri whole-cells immobilized on agarose beads proved to be an interesting option to transform this biotransformation in a preparative process. The entrapment matrix provided a useful and resistant multipurpose biocatalyst regarding its stability, mechanical strength, microbial viability and reuse. Immobilized biocatalyst retained the initial activity for up to 1 year storage and after 10 years, the biocatalyst did not show cell leaking and still exhibited residual activity. In addition, the biocatalyst could be reused in batch 68 times keeping up to 50% of the initial biocatalytic activity and for at least 124 h in a continuous process.