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Abstract: The use of organic solvent-based media for microbial 9α-hydroxylation of androstenedione (AD) by resting Rhodococcus sp. cells was evaluated. Product yields higher than 90% were observed in a two-phase phthalate-buffer transformation medium (3:1, v/v) containing 1.0gL−1 AD. The results suggest that in these conditions the reaction of Δ1-dehydrogenation is considerably inhibited. The successful hydroxylation reaction with a product yield exceeding 60% was found to take place also in a phthalate medium under simultaneous forced aeration and maintenance of a minimum water content of about 3% (v/v). [Copyright &y& Elsevier]

The applicability of a recently published modification of the chemostat, named “titrostat”, for microbial continuous-flow purification of toluene-contaminated air is discussed. This article describes the operative range and the toluene elimination efficiency of a 2-l titrostat running with a mixed bacterial culture dominated by two Acinetobacter species: A. calcoaceticus and A. radioresistens. The study focuses on the kinetics and stoichiometry of the process. Special attention is paid to the peculiarities of toluene as an unconventional growth substrate having high carbon and energy content. Removal productivity as high as 2.24 g l-1 h-1 with 99.9% elimination efficiency was observed at air flow rate 60 l h-1, temperature 32show $132#°show $132#C, pH 6.2, toluene concentration in the inlet air 37.4 mg l-1 and titrant solution containing NH3 at 1.87 g l-1. The maximum biomass yield from assimilated toluene, Ysm=0.880±0.011, and a rate of substrate expenditures for cell maintenance, ms=0.022±0.002 h-1, were estimated. [ABSTRACT FROM AUTHOR]

The selective side-chain cleavage of β-sitosterol by free cells of Mycobacterium sp. NRRL B-3805 is a well-established multi-enzymatic process for the production of the pharmaceutical steroid precursors androstenedione (AD) and androstadienedione (ADD). In this study, bis(2-ethylhexyl) phthalate (BEHP) was used as a reaction medium for carrying out the process with freely suspended cells. The work aimed to show that microbial sitosterol side-chain cleavage is possible in this essentially mono-phasic organic medium, provided that some important parameters are adequately controlled. The effects of the biocatalyst/substrate mass ratio, system aeration rate and minimum buffer addition to the organic medium on the product yield and the reaction rate were thus evaluated. [ABSTRACT FROM AUTHOR]

The present work aimed at quantifying the viability and morphological changes occurring during the time course of the side-chain cleavage of β-sitosterol, in aqueous, two-phase organic-aqueous and organic media by free resting cells of Mycobacterium sp. NRRL B-3805. The solvent used was bis(2-ethylhexyl) phthalate (BEHP). A 66.3% reduction in cell viability was observed after 24 h when the cells were incubated in phosphate buffer only, but the percentage of viable cells was constant thereafter. In biphasic systems with BEHP, cell viability was maintained at higher values in the first 48 h, during which complete degradation of substrate was achieved. The availability of oxygen, which should be higher in the biphasic system than in the aqueous system, and of a carbon and energy source, thus seem important for the cells to retain their viability. In biphasic systems, cells tended to shrink and decrease their surface roughness, i.e. to decrease their surface area, possibly as a way to protect themselves from mechanical stress due to the presence of organic-aqueous interfacial forces, which resulted in disaggregation of cell clusters. A method used to visualise BEHP droplets with a standard optical microscope showed that the cells adhered to the surface of the solvent droplets, but no cells were observed inside these. In pure BEHP medium, cells retained their viability level for at least 150 h, independently of a pre-incubation period, which did not seem to induce any adaptation effect. Solvent biocompatibility, higher oxygen availability and reduced interfacial stress could have contributed to this maintenance of viability. [ABSTRACT FROM AUTHOR]

Steroid compounds can be ranked among the most widely marketed products from the pharmaceutical industry. Highly specific reactions are required to produce functionalized compounds with therapeutic use and commercial value. The complexity of steroid molecules renders the use of biocatalysts particularly interesting, due to the high regio- and stereo-selectivity of the reactions to be performed. These characteristics, together with the mild conditions required for bioconversions, led to the development of high yield biological production processes, which are more environmentally friendly than their chemical synthesis counterparts, a feature that is presently a major concern of industrialists. Although some of these bioconversions are well-established, efforts are ongoing in order to increase the efficiency of the existing processes as well as to identify new potentially useful bioconversions. In this work an overview of recent developments on the use of microorganisms for steroid production is presented. [Copyright &y& Elsevier]