RESUMO
BACKGROUND: Microbial synthesis of oleochemicals derived from native fatty acid (FA) metabolism has presented significant advances in recent years. Even so, native FA biosynthetic pathways often provide a narrow variety of usually linear hydrocarbons, thus yielding end products with limited structural diversity. To overcome this limitation, we took advantage of a polyketide synthase-based system from Mycobacterium tuberculosis and developed an Escherichia coli platform with the capacity to synthesize multimethyl-branched long-chain esters (MBE) with novel chemical structures. RESULTS: With the aim to initiate the characterization of these novel waxy compounds, here, we describe the chassis optimization of the MBE producer E. coli strain for an up-scaled oil production. By carrying out systematic metabolic engineering, we improved the final titer to 138.1 ± 5.3 mg MBE L-1 in batch cultures. Fed-batch microbial fermentation process was also optimized achieving a maximum yield of 790.2 ± 6.9 mg MBE L-1 with a volumetric productivity of 15.8 ± 1.1 mg MBE (L h)-1. Purified MBE oil was subjected to various physicochemical analyses, including differential scanning calorimetry (DSC) and pressurized-differential scanning calorimetry (P-DSC) studies. CONCLUSIONS: The analysis of the pour point, DSC, and P-DSC data obtained showed that bacterial MBE possess improved cold flow properties than several plant oils and some chemically modified derivatives, while exhibiting high oxidation stability at elevated temperatures. These encouraging data indicate that the presence of multiple methyl branches in these novel esters, indeed, conferred favorable properties which are superior to those of linear esters.
RESUMO
A positive relationship between species richness and productivity is often observed in nature, but the causes remain contentious. One mechanism, the 'more individuals hypothesis' (MIH), predicts richness increases monotonically with density, as a function of resource flux. To test the MIH, we manipulated resource abundance in a community of tropical rainforest litter ants and measured richness and density responses. A unimodal relationship between richness and density most closely fitted the control and disturbance (resource removal) treatments in contrast to expectations of the MIH. Resource addition resulted in a monotonic increase in richness relative to density, a shift from the pattern in the control. In the disturbance treatment, richness was greater than in the control, opposite to expectations of the MIH. While large-scale correlations between ant diversity and net primary productivity or temperature are reconcilable with the MIH, key elements of the hypothesis are not supported.