Combining co-culturing of Paenibacillus strains and Vitreoscilla hemoglobin expression as a strategy to improve biodesulfurization.

Enhancement of the desulfurization activities of Paenibacillus strains 32O-W and 32O-Y were investigated using dibenzothiophene (DBT) and DBT sulfone (DBTS) as sources of sulphur in growth experiments. Strains 32O-W, 32O-Y and their co-culture (32O-W plus 32O-Y), and Vitreoscilla hemoglobin (VHb) expressing recombinant strain 32O-Yvgb and its co-culture with strain 32O-W were grown at varying concentrations (0·1-2 mmol l-1 ) of DBT or DBTS for 96 h, and desulfurization measured by production of 2-hydroxybiphenyl (2-HBP) and disappearance of DBT or DBTS. Of the four cultures grown with DBT as sulphur source, the best growth occurred for the 32O-Yvgb plus 32O-W co-culture at 0·1 and 0·5 mmol l-1 DBT. Although the presence of vgb provided no consistent advantage regarding growth on DBTS, strain 32O-W, as predicted by previous work, was shown to contain a partial 4S desulfurization pathway allowing it to metabolize this 4S pathway intermediate.

Enhancement of ethanol production from potato-processing wastewater by engineering Escherichia coli using Vitreoscilla haemoglobin.

UNLABELLED: Ethanologenic Escherichia coli strain FBR5 was transformed with the Vitreoscilla haemoglobin (VHb) gene (vgb) in two constructs (resulting in strains TS3 and TS4). Strains FBR5, TS3 and TS4 were grown at two scales in LB medium supplemented with potato-processing wastewater hydrolysate. Aeration was varied by changes in the medium volume to flask volume ratio. Parameters measured included culture pH, cell growth, VHb levels and ethanol production. VHb expression in strains TS3 and TS4 was consistently correlated with increases in ethanol production (5-18%) under conditions of low aeration, but rarely did this occur with normal aeration. The increase in ethanol yields under low aeration conditions was the result of enhancement of ethanol produced per unit of biomass rather than enhancement of growth. 'VHb technology' may be a useful adjunct in the production of biofuels from food-processing wastewater. SIGNIFICANCE AND IMPACT OF STUDY: Genetic engineering using Vitreoscilla haemoglobin (VHb) has been shown previously to increase ethanol production by Escherichia coli from fermentation of the sugars in corn fibre hydrolysate. The study reported here demonstrates a similar VHb enhancement of ethanol production by fermentation of the glucose from potato waste water hydrolysate and thus extends the list of sugar containing waste products from which ethanol production may be enhanced by this strategy.

Inactivation of Escherichia coli and Listeria monocytogenes on iceberg lettuce by dip wash treatments with organic acids.

AIMS: To study and compare the efficacy of organic acids and chlorine dipping in inactivation of Escherichia coli and Listeria monocytogenes on fresh-cut iceberg lettuce. METHODS AND RESULTS: Fresh-cut iceberg lettuce leaves were inoculated with E. coli or L. monocytogenes. After inoculation, samples were stored at 4 degrees C for 24 h and dipped in organic acid or chlorine solutions for 2 and 5 min. E. coli and L. monocytogenes were enumerated on selective media. Treatment of fresh-cut iceberg lettuce with chlorine solution caused 1.0 and 2.0 log(10) CFU g(-1) reductions in the number of L. monocytogenes and E. coli, respectively. Maximum reduction for E. coli (about 2.0 log(10) CFU g(-1)) was obtained for samples dipped in lactic or citric acids while maximum reduction for L. monocytogenes (about 1.5 log(10) CFU g(-1)) was attained for samples dipped in lactic acid. CONCLUSIONS: Dipping of iceberg lettuce in 0.5% citric acid or 0.5% lactic acid solution for 2 min could be as effective as chlorine for reducing microbial populations on fresh-cut iceberg lettuce. SIGNIFICANCE AND IMPACT OF THE STUDY: Dipping in solutions containing organic acids is shown to be effective to reduce E. coli and L. monocytogenes on fresh-cut iceberg lettuce.