Biosurfactant production by cultivation of Bacillus atrophaeus ATCC 9372 in semidefined glucose/casein-based media

Biosurfactants are proteins with detergent, emulsifier, and antimicrobial actions that have potential application in environmental applications such as the treatment of organic pollutants and oil recovery. Bacillus atrophaeus strains are nonpathogenic and are suitable source of biosurfactants, among which is surfactin. The aim of this work is to establish a culture medium composition able to stimulate biosurfactants production by B. atrophaeus ATCC 9372. Batch cultivations were carried out in a rotary shaker at 150 rpm and 35 degrees C for 24 h on glucose-and/or casein-based semidefined culture media also containing sodium chloride, dibasic sodium phosphate, and soy flour. The addition of 14.0 g/L glucose in a culture medium containing 10.0 g/L of casein resulted in 17 times higher biosurfactant production (B(max)=635.0 mg/L). Besides, the simultaneous presence of digested casein (10.0 g/L), digested soy flour (3.0 g/L), and glucose (18.0 g/L) in the medium was responsible for a diauxic effect during cell growth. Once the diauxie started, the average biosurfactants concentration was 16.8% less than that observed before this phenomenon. The capability of B. atrophaeus strain to adapt its own metabolism to use several nutrients as energy sources and to preserve high levels of biosurfactants in the medium during the stationary phase is a promising feature for its possible application in biological treatments.     

Measuring electron sharing between atoms in first-principle simulations

Calculations of large scale electronic structure within periodic boundary conditions, mostly based on solid state physics, allow the modeling of atomic forces and molecular dynamics for atomic assemblies of 100–1000 atoms, thus providing complementary information in material and macromolecular sciences. Nevertheless, these methods lack connections with the chemistry of simple molecules as isolated entities. In order to contribute to establish a conceptual connection between solid state physics and chemistry, the calculation of the extent of electron sharing between atoms, also known as delocalization index, is performed on simple molecules and on complexes with transition metal atoms, using density functional calculations where the Kohn–Sham molecular orbitals are represented in terms of plane waves and in periodic boundary conditions. These applications show that the useful measure of electron sharing between atomic pairs can be recovered from density functional calculations using the same set-up applied to large atomic assemblies in condensed phases, with no projections of molecular orbitals onto atomic orbitals.     

Landau description for an atomic screened system: the charge symmetry breaking effect

We have examined the presence of a charge symmetry breaking in a screened system. Using a Thomas-Fermi-type potential and a simple mathematical model, we show that screening on the nuclear charge α induces a charge parametrization α→(α,β) in which appears a new dual charge β in the system. Considering this method, the binding energy of electron becomes invariant under parity symmetry for an order parameter ρ=β-α. We find nontrivial solutions for ρ at the minimum of energy which leads to the broken parity symmetry. The equations obtained for this new screening approach is very similar to the Landau theory of phase transition.