Effects of a low-voltage electric pulse charged to culture soil on plant growth and variations of the bacterial community

This study was conducted to verify the effect of an electric pulse on growth of crops (lettuce and hot pepper) that were cultivated in lab-scale soil. The electric pulse generated from direct-circuited 2, 4, 6, 8, and 10 V of electricity by periodic exchange of the anode and cathode was charged to a culture soil that is an electrically pulsed culture soil (EPCS) but not charged to a conventional culture soil (CCS). Growth of lettuce increased and growth duration of hot pepper plants was more prolonged at 4, 6, 8, and 10 V of EPCS than at 2 V of EPCS and CCS. The fruiting duration and yield of hot pepper fruits were proportional to the growth duration of the hot pepper plants. Temperature gradient gel electrophoresis (TGGE) patterns of 16S-rDNA obtained from the bacterial community inhabiting the CCS and EPCS were identical at the initial time and did not change significantly at days 28 and 56 of cultivation. The bacterial communities inhabiting the surface of lettuce roots were not influenced by the electric pulse but were significantly different from those inhabiting the culture soil based on the TGGE patterns. Growth of lettuce and hot pepper plants that were cultivated in 4 - 10 V of EPCS may increase;however, the bacterial community inhabiting the soil and the surface of plant roots may not be influenced by an electric pulse.

Effect of electric pulse charged to culture soil on improvement of nutritional soil condition and growth of lettuce (<i>Lactuca sative</i>L.)

This study is intended to measure variations of nutritional soil condition and mass spectrometric patterns to describe the specific effects of electric pulse charged to culture soil which induced an increase of lettuce growth. In a previous study, lettuce cultivated in an electrically pulsed culture soil (EPCS) grew more actively than those in a conventional culture soil (CCS). Lettuce growth increased about 20% more in EPCS than CCS during cultivated for 21 days in this study. Content of nutrient salts and minerals varied in CCS and EPCS when assayed after the period of lettuce cultivation. Ammonium content in CCS was higher than that in EPCS but nitrate content was opposite of the ammonium. Inorganic N-compounds in EPCS was about 2.5 times higher than that in CCS. Content of phosphate in CCS increased greatly by lettuce cultivation but was about 2 times lower than that in EPCS. Contents of minerals in EPCS were relatively higher than those in CCS excepting Fe. Patterns of chromatography and mass spectrometry for water soluble compounds extracted from lettuces cultivated in EPCS were considerably different from those in CCS. Conclusively, electric pulse caused increased lettuce growth, improved nutritional soil conditions, and varied mass spectrometric patterns.

Conversion of Carbon Dioxide to Metabolites by <i>Clostridium acetobutylicum</i>KCTC1037 Cultivated with Electrochemical Reducing Power

In this research, metabolic fixation of CO2 by growing cells of C. acetobutylicum cultivated with electrochemical reducing power was tested on the basis of the metabolites production and genes expression. In cyclic voltammetry, electrochemical oxidation and reduction reaction of neutral red (NR) immobilized in intact cells of C. acetobutylicum was stationarily repeated like the soluble one in the condition without CO2 but the electrochemical reduction reaction was selectively increased by addition of CO2. In electrochemical bioreactor, the modified graphite felt cathode with NR (NR-cathode) induced C. acetobutylicum to generate acetate, propionate, and butyrate from CO2 in defined medium. When H2 and CO2 were used as an electron donor and an electron acceptor, respectively, C. acetobutylicum also produced the same metabolites in a defined medium. C. acetobutylicum was not grown in the defined medium without substituted electron donors (H2 or electrochemical reducing power). C. acetobutylicum cultivated with electrochemical reducing power produced more butyrate than acetate in complex medium but produced more acetate than butyrate in defined medium. The genes of encoding the enzymes catalyzing acetyl-CoA in C. acetobutylicum electrochemically cultivated in defined medium than conventionally cultivated in complex medium. These results are a clue that C. acetobutylicum may metabolically convert CO2 to metabolites and produce free energy from the electrochemical reducing power.

Activation of Ethanol Production by Combination of Recombinant <i>Ralstonia eutropha</i>and Electrochemical Reducing Power

Ralstonia eutropha was genetically modified to induce ethanol production from glucose. An electrochemical bioreactor was prepared to generate electrochemical reducing power coupled to regeneration of NADH. Growing cells of recombinant R. eutropha produced about 29 mM of ethanol in conventional conditions and 56 mM of ethanol in electrochemically reduced conditions from 100 mM glucose. Grown cells of the recombinant produced about 52 mM of ethanol in conventional conditions and 142 mM of ethanol in electrochemically reduced condition from 100 mM glucose. These results are a clue that electrochemical reducing power can induce the recombinant R. eutropha to produce more ethanol coupled to increase of NADH/NAD+ ratio.

Enrichment and Isolation of CO₂-Fixing Bacteria with Electrochemical Reducing Power as a Sole Energy Source

Enrichment of bacteria capable of growing with electrochemical reducing power and CO2 was accomplished using a plate-type electrochemical bioreactor (PEB). A bacterial source obtained from wastewater treatment reactant and forest soil was cultivated on carbonate-based mineral agar medium prepared in the PEB (PEB-carbonate agar). According to the pyrosequencing analyses, the abundance of Betaproteobacteria and Gammaproteobacteria at the phylum level, and Achromobacter, Alcaligenes, and Pseudomonas at the genus level were selectively increased after the electrochemical enrichment culture. Finally, one genus of bacterium that was autotrophically grown on the PEB-carbonate agar was identified as Alcaligenes. This bacterium may be useful to fix atmospheric CO2 with electrochemical energy obtained from the solar cell.

Mineralization of Petroleum Contaminated Wastewater by Co-Culture of Petroleum-Degrading Bacterial Community and Biosurfactant-Producing Bacterium

Activity of a crude biosurfactant extracted from the culture fluid of Serratia sp. that was isolated from riverbed soil was shown to increase in proportion to the cultivation time, and was higher at pH 8 than at pH 7. Serratia sp. grew in the mineral-based medium with soybean oil but was not with kerosene-diesel. The petroleum-degrading bacteria—Acinetobacter sp., Pseudomonas sp., Paracoccus sp., and Cupriavidus sp.—were isolated from a specially designed enrichment culture. The efficiency of mineralization of wastewater contaminated with kerosene and diesel (WKD) by the petroleum-degrading bacterial community (PDBC) was enhanced significantly by addition of the crude biosurfactant. The efficiency of mineralization of the WKD was also about 2 times boosted by co-culture of Serratia sp. and PDBC. Bacterial community of Serratia sp. and PDBC co-cultivated in the WKD was maintained for at least 8 days according to the TGGE pattern of 16S rDNA obtained from the bacterial culture. In conclusion, the co-culture of Serratia sp. and PDBC is an applicable technique for the mineralization of wastewater contaminated with petroleum, which may substitute for chemical or biological surfactant.