Every day, more evidence accumulates, leading to the conclusion that the stereoelectronic model through the nO → σ*C─O interaction is of minor relevance or even inoperative to explain conformational preference in the specific O─C─O segment. In the present study, dimethoxymethane (DMM) and some model spiroketals were chosen to develop a reliable and easy to apply methodology that is simple to interpret by experimental chemists. The general conformation observed in these molecules, present in many biologically active natural products, is the gauche‐gauche (g,g) in DMM and bis‐diaxial in spiroketals. To study this conformational preference, this paper presents a new approach, where general trends for the atomic and molecular energetic components, as well as localization and delocalization indices, and their bonded (Δb) and nonbonded (Δnb) electronic contributions are analyzed. In addition, group contributions to the electron localization and polarization are also defined, agreeing with the conformational preference. It is clear that electronic localization/delocalization is capable of reproducing experimental observations, showing an adequate correlation of this property to the cos θ term in the context of Pople's analysis. It is proposed that electron delocalization between electronegative atoms or total delocalization between nonbonded atoms is not the major contributors to the axial conformational preference observed in spiroketals. Conformational preference shows defined trends in terms of group delocalization in DMM and ring localization and charge transfer between groups in spiroketals. This way, electronic delocalization can be used to evaluate the anomeric effect, using just a few parameters, which makes the method broadly functional.

A new bacterial strain has been isolated from the microbiome of solar panels and classified as Arthrobacter sp. Helios according to its 16S rDNA, positioning it in the “Arthrobacter citreus group.” The isolated strain is highly tolerant to desiccation, UV radiation and to the presence of metals and metalloids, while it is motile and capable of growing in a variety of carbon sources. These characteristics, together with observation that Arthrobacter sp. Helios seems to be permanently prepared to handle the desiccation stress, make it very versatile and give it a great potential to use it as a biotechnological chassis. The new strain genome has been sequenced and its analysis revealed that it is extremely well poised to respond to environmental stresses. We have analyzed the transcriptional response of this strain to PEG6000-mediated arid stress to investigate the desiccation resistance mechanism. Most of the induced genes participate in cellular homeostasis such as ion and osmolyte transport and iron scavenging. Moreover, the greatest induction has been found in a gene cluster responsible for biogenic amine catabolism, suggesting their involvement in the desiccation resistance mechanism in this bacterium.

A new bacterial strain highly tolerant to desiccation and to UV radiation has been isolated from the microbiome of solar panels. This strain showed a high xerotolerance in the exponential and the stationary phase of growth and it has been classified as Arthrobacter sp. Helios according to its 16S rDNA, positioning this new strain in the Arthrobacter citreus group. The complete genome of Arthrobacter sp. Helios consists in a single circular chromosome of 3,895,998 bp, with a 66% GC content and no plasmids. A total of 3,586 genes were predicted, of which 2,275 protein-encoding genes were functionally assigned. The genome analysis suggests that it is motile, ecologically versatile, and capable of growing in a variety of carbon sources and well poised to respond to environmental stresses. Using PEG6000 to mimic arid stress conditions, we have studied the transcriptional response of this strain to matric stress when cells are cultured on media containing 10% (PEG10) and 35% PEG (PEG35). The transcriptomic analysis revealed that cells can be easily adapted to moderate matric stress (PEG10) by modifying the expression of a small number of genes to maintain a high growth rate, while a higher matric stress (PEG35) altered the expression of many more genes. Remarkably, these metabolic changes do not confer the cells a higher tolerance to desiccation, suggesting that mechanisms to support matric stress and desiccation tolerance are different. The peculiar observation that Arthrobacter sp. Helios seems to be permanently prepared to handle the desiccation stress makes it an exciting chassis for biotechnological applications.

The production of 4-androstene-3,17-dione (AD) from natural sterols has been improved by deleting the MSMEG_6561 gene ofMycolicibacterium smegmatiswhich encodes an aldolase. The deletion of this gene increases the AD production yield avoiding the production of 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) as by-product and the drawbacks in the AD purification. TheMSMEG_6561gene encodes the only enzyme within theM. smegmatisgenome responsible for the aldolytic activity transforming 22-hydroxy-3-oxo-cholest-4-ene-24-carboxyl-CoA (22-OH-BCN-CoA) into the 4-HBC precursor (20S)-3-oxopregn-4-ene-20-carboxaldehyde (3-OPA). The molar yield of AD production using the MS6039-5941-6561 triple mutant strain was checked in flasks and bioreactor improving very significantly compared with the previously described MS6039-5941 strain.

Mycobacterial mutants blocked in ring degradation constructed to achieve C19 synthons production, also accumulate by‐products such as C22 intermediates throughout an alternative pathway reducing the production yields and complicating the downstream purification processing of final products. In this work, we have identified the MSMEG_6561 gene, encoding an aldolase responsible for the transformation of 22‐hydroxy‐3‐oxo‐cholest‐4‐ene‐24‐carboxyl‐CoA (22‐OH‐BCN‐CoA) into the 22‐hydroxy‐23,24‐bisnorchol‐4‐ene‐3‐one (4‐HBC) precursor (20S)‐3‐oxopregn‐4‐ene‐20‐carboxaldehyde (3‐OPA). The deletion of this gene increases the production yield of the C‐19 steroidal synthon 4‐androstene‐3,17‐dione (AD) from natural sterols, avoiding the production of 4‐HBC as by‐product and the drawbacks in the AD purification. The molar yield of AD production using the MS6039‐5941‐6561 triple mutant strain was checked in flasks and bioreactor improving very significantly compared with the previously described MS6039‐5941 strain.