Resuscitation and quantification of stressed Escherichia coli K12 NCTC8797 in water samples

The aim of this study was to investigate the impact on numbers of using different media for the enumeration of Escherichia coli subjected to stress, and to evaluate the use of different resuscitation methods on bacterial numbers. E. coli was subjected to heat stress by exposure to 55 °C for 1 h or to light-induced oxidative stress by exposure to artificial light for up to 8 h in the presence of methylene blue. In both cases, the bacterial counts on selective media were below the limits of detection whereas on non-selective media colonies were still produced. After resuscitation in non-selective media, using a multi-well MPN resuscitation method or resuscitation on membrane filters, the bacterial counts on selective media matched those on non-selective media. Heat and light stress can affect the ability of E. coli to grow on selective media essential for the enumeration as indicator bacteria. A resuscitation method is essential for the recovery of these stressed bacteria in order to avoid underestimation of indicator bacteria numbers in water. There was no difference in resuscitation efficiency using the membrane filter and multi-well MPN methods. This study emphasises the need to use a resuscitation method if the numbers of indicator bacteria in water samples are not to be underestimated. False-negative results in the analysis of drinking water or natural bathing waters could have profound health effects

Effect of O-cresol, resorcinol and hydroquinone on citric acid productivity by Aspergillus niger in stirred fermentor

Effects of o-cresol, resorcinol and hydroquinone, which are. toxic chemicals, on citric acid biosynthesis and biomass in the artificial culture setting of Aspergillus niger using batch fermenter are examined in the most favourable fermentation conditions and a model is proposed. According to this model, maximum citric acid concentration is 48.3 g L-1 in a culture that does not contain any toxic chemicals, whereas the maximum concentrations obtained in cultures containing 15 mg L-1 o-cresol, 45 mg L -1 resorcinol and 35 mg L-1 hydroquinone are 86.7, 82.8 and 86.8 g L-1, respectively. Moreover, addition of toxic chemicals to the culture reduces fermentation time by 24 h

Biosorption and separation/preconcentration of lead and nickel on rhodococcus ruber biomass

At the present time emphasis is given to the utilization of microorganisms because of their great ability to absorb metal ions from aqueous solution. Hence, in this study, Pb2+ and Ni2+ ions at trace levels were separated and preconcentrated on a column containing a bacterium, Rhodococcus ruber bacterial biomass (RrBB), as a new solid phase extraction technique prior to their flame atomic absorption spectrometry (FAAS) determination. The optimum experimental and analytical parameters such as pH of sample solution, volume and concentration of eluent, flow rate of sample solution and eluent, sample volume, effect of common matrix ions and capacity of biosorbent were investigated and optimized. Under the optimized conditions, the preconcentration factors for Pb2+ and Ni2+ were calculated as 150 and 100, respectively. The analytical detection limits for Pb2+ and Ni2+ were 0.32µgL-1 and 0.24 µgL-1 respectively. The Langmuir monolayer adsorption capacity of biomass was estimated as 42.91 and 6.78 mg g-1 for Pb2+ and Ni2+, respectively. Certified reference material (NIST SRM 1640a) was also used to confirm the accuracy of the method. The developed solid phase extraction method was applied successfully for the determination of Pb2+ and Ni2+ in various water samples. © by PSP