A new cultivation method for microbial oil production: cell pelletization and lipid accumulation by Mucor circinelloides

The recent energy crisis has triggered significant attention on the microbial synthesis of lipids, which comprise the raw material for biodiesel production. Microbial oil accumulation with filamentous fungi has great potential because filamentous fungi can form pellets during cell growth, and these pellets are much easier to harvest from cell broth. This paper focuses on the cell pelletization process of the oleaginous Mucor circinelloides. We have studied the effect of various cultural conditions on pelletized cell growth and lipid accumulation. This study is the first to report that pH adjustment during cell growth plays a key role in pellet formation of M. circinelloides and describes a handy method by which to induce cell pelletization in submerged fungal cultivation. Our study reveals that cell growth and lipid production are not significantly affected by pelletization and that lipid accumulation is triggered at stressed conditions, such as a high carbon-to-nitrogen ratio and high temperature

Microstructure evolution under the space-time variational solidification conditions in a melt pool: A multi-scale simulation study

The properties of welded components are dominated by the microstructure evolution in the pool, where the solidification conditions are space-time variational. To represent the variational solidification conditions in the pool, the multi-scale simulation is carried out in this paper, combining microscopic Phase-Field (PF) equations with macroscopic thermal processes. First, two different models, the GR model and TF model, are employed to simulate the single crystal solidification at a local region of pool. Results suggest the TF model is more suitable to reflect the variational conditions than the GR model. Then the single-crystal solidification and poly-crystal solidification at the whole region of pool are carried out through the TF model. The results indicate the space-time variabilities of solidification conditions across the pool. Meanwhile, the variational solidification conditions influence the microstructure evolution significantly, including the onset of initial instability at the epitaxial growth stage and the directional evolutions of the converging grain boundaries (GBs) and diverging GBs at the competitive growth stage. Moreover, the formation of axial grain structures is observed, which can be regarded as the competition between the grains along the axial direction and radial direction. This study indicates the necessity of considering variational conditions in a pool. Meanwhile, the PF model can simulate microstructure evolution under variational conditions accurately, which has a great potential for investigating solidification dynamics in a melt pool.Comment: 30pages, 14 figure