Electroporation and expression of the broad host-range plasmid pRK2501 in Azotobacter vinelandii

Azotobacter vinelandii: the source of 100 years of discoveries and many more to come

Azotobacter vinelandii has been studied for over 100 years since its discovery as an aerobic nitrogen-fixing organism. This species has proved useful for the study of many different biological systems, including enzyme kinetics and the genetic code. It has been especially useful in working out the structures and mechanisms of different nitrogenase enzymes, how they can function in oxic environments and the interactions of nitrogen fixation with other aspects of metabolism. Interest in studying A. vinelandii has waned in recent decades, but this bacterium still possesses great potential for new discoveries in many fields and commercial applications. The species is of interest for research because of its genetic pliability and natural competence. Its features of particular interest to industry are its ability to produce multiple valuable polymers - bioplastic and alginate in particular; its nitrogen-fixing prowess, which could reduce the need for synthetic fertilizer in agriculture and industrial fermentations, via coculture; its production of potentially useful enzymes and metabolic pathways; and even its biofuel production abilities. This review summarizes the history and potential for future research using this versatile microbe.

Optimization of electrotransformation conditions for Propionibacterium acnes

Propionibacterium acnes has been known to be involved in the pathology of acne. However, the definite mechanism in the development of acne and the inflammation are unknown. For P. acnes, a transformation method has not been established, although it is believed to be a basic tool for gene manipulation. This study attempted to develop a P. acnes transformation method by using electroporation. Various parameters were used to develop and optimize the transformation of P. acnes. Among them two factors were crucial in the transformation for P. acnes: one was the E. coli strain from which the plasmid DNA had been isolated and the other the growth temperature of P. acnes-competent cells. It was essential to prepare plasmid DNA from a dam(-) E. coli strain, ET12567. When plasmid DNAs isolated from the other E. coli strains such as JM109 and HB101 were tested, transformation efficiency was extremely low. When P. acnes cells were cultivated at 24 degrees C for competent cell preparation, transformation efficiency increased considerably. When plasmid DNA isolated from a dam(-) mutant strain of E. coli was used for transformation of P. acnes which had been grown at 24 degrees C, maximum transformation efficiency of 1.5 x 10(4) transformants per mug of plasmid DNA was obtained at a field strength of 15 kV/cm with a pulse time of 3.2 ms. This is believed to be the first report on the transformation of P. acnes which can be employed for gene manipulations including knock-out of specific genes.

Stable electrotransformation of symbiont candidate diazotrophic bacterium with plasmids carrying selectable and screenable marker genes

Nitrogen-fixing symbioses had been established between the originally asymbiotic soil bacterium Azotobacter vinelandii CCM289 and different lower and higher plant species. Better characterization and further development of such artificial systems require a reliable genetic transformation method for the introduction of marker genes into symbiont candidates. The performance of electroporation was evaluated using pJB3 (4.8 kb), pBI121 (12.8 kb) and pFAJ31.2 (24 kb) plasmid DNAs containing selectable (Ap, Km, Tc) and screenable (gusA, lacZ) marker genes. The adapted methods for the preparation of transformation-competent azotobacters and their electroporation (18 kV/cm electric field strength, 5 ms time constant, 0 degree C) provided up to 6.8 x 10(5) transformants per microgram plasmid DNA, which is about 10(3) times the transformation efficiency achieved in control experiments. No electrotransformants were obtained with the 24-kb pFAJ31.2. The size of plasmid DNA did not significantly affect the efficiency of transformation. Transformants were able to grow at antibiotic concentrations that were 100-200 times greater than the lowest amounts that completely inhibited the growth of wild-type bacteria. A constitutive expression of gusA gene was observed in transformants with the CaMV 35S promoter-gusA fusion containing pBI121, while lacZ expression was not detected under the control of the lac promoter in pJB3 transformants. Electroporated plasmids were reisolated from transformants in their original form, while non-transformed bacteria did not contain indigenous plasmids. PCR amplification and Southern DNA blot hybridization showed the integration of plasmid DNA into the host genome as well. Transformants retained their nitrogen-fixing ability and had normal morphological and growth characteristics. Experimental findings proved the stable maintenance of plasmid DNA in azotobacters, making possible the routine transformation and detection of these symbiont candidates.