Production of fatty acids by engineered Ogataea polymorpha / 生物工程学报

Fatty acids (FA) are widely used as feed stocks for the production of cosmetics, personal hygiene products, lubricants and biofuels. Ogataea polymorpha is considered as an ideal chassis for bio-manufacturing, due to its outstanding characteristics such as methylotroph, thermal-tolerance and wide substrate spectrum. In this study, we harnessed O. polymorpha for overproduction of fatty acids by engineering its fatty acid metabolism and optimizing the fermentation process. The engineered strain produced 1.86 g/L FAs under the optimized shake-flask conditions (37℃, pH 6.4, a C/N ratio of 120 and an OD600 of seed culture of 6-8). The fed-batch fermentation process was further optimized by using a dissolved oxygen (DO) control strategy. The C/N ratio of initial medium was 17.5, and the glucose medium with a C/N ratio of 120 was fed when the DO was higher than 30%. This operation resulted in a titer of 18.0 g/L FA, indicating the potential of using O. polymorpha as an efficient cell factory for the production of FA.

First isolation of the Stephanoascus ciferrii in feline otitis in Brazil

Ear infections in cats are uncommon, especially involving yeasts. This report describes the first isolation of the Stephanoascus ciferrii, teleomorph of the Candida genus, in a case of feline otitis in Brazil. The identification and characterization of Stephanoascus ciferrii were confirmed by the Vitek2 System (BioMerieux ®).

Interaction of hexadecyltrimethylammonium bromide with yeast cells.

The interaction of hexadecyltrimethylammonium bromide (CTAB) with two yeast cells, Kluyveromyces fragilis and Saccharomyces cerevisiae, has been studied. Strong binding of CTAB to the cell was inferred from 1H and 13C NMR studies, the probable site of binding being the cell-surface. 13C and 31P NMR studies have indicated facilitation of free passage of molecules from outside to inside the cell and vice versa on treatment with CTAB. 31P NMR studies showed that intracellular pH (pHi) was affected in presence of CTAB and the rate of exchange of H+ and PO4(-3) between outside and inside of the cell was 508 s-1. CTAB treatment of yeast cells also affected pH and conductance measurements of the cell-suspension. There was a marked difference in the pH changes around the critical micellar concentration (CMC) of CTAB. The observed pH changes were dependent on (i) CTAB concentration, (ii) pH of the cell-suspension and (iii) pK values of groups from molecules released from the cell. Also, it was shown that ionisation of phosphate diester from polar head groups of membranes constituting cell surface enhanced CTAB binding. Conductance measurements have shown that observed changes were independent of the concentration of yeast cells, but probably dependent on CMC of CTAB.

Hydrocarbon emulsification by Candida tropicalis and Debaryomyces polymorphus.

Potentiality of C. tropicalis and D. polymorphus, to produce surface active compounds (bioemulsifiers/biosurfactants) during shake cultivation on hexadecane and oily waste was studied. Better emulsification activity, specific towards aromatic hydrocarbons, was observed with C. tropicalis culture broth. Emulsification activity of culture broth was quite stable and was unaffected by change in pH and by increasing the concentration of NaCl up to 5%. The activity was marginally affected by heating in boiling water bath for 15 min, but inhibited to the tune of 90% by 0.3% CaCl2. The isolated bioemulsifying factor contained 40, 22 and 17.5% lipid, protein and carbohydrate, respectively.