Butanol is a promising next generation fuel and a bulk chemical precursor. Although clostridia are the primary industrial microbes for the fermentative production of 1-butanol, alternative engineered hosts have the potential to generate 1-butanol from alternative carbon feedstocks via synthetic metabolic pathways. Methylobacterium extorquens AM1, a facultative methylotrophic α-proteobacterium, is a model system for assessing the possibility of generating products such as 1-butanol from one-carbon and two-carbon feedstocks. Moreover, the core methylotrophic pathways in M. extorquens AM1 involve unusual coenzyme A (CoA)-derivative metabolites, such as crotonyl-CoA, which is a precursor for the production of 1-butanol.

The toxicity of alcohols is one of the major roadblocks of biological fermentation for biofuels production. Methylobacterium extorquens AM1, a facultative methylotrophic α-proteobacterium, has been engineered to generate 1-butanol from cheap carbon feedstocks through a synthetic metabolic pathway. However, M. extorquens AM1 is vulnerable to solvent stress, which impedes further development for 1-butanol production. Only a few studies have reported the general stress response of M. extorquens AM1 to solvent stress. Therefore, it is highly desirable to obtain a strain with ameliorated 1-butanol tolerance and elucidate the molecular mechanism of 1-butnaol tolerance in M. extorquens AM1 for future strain improvement.

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.