Browsing by Author "Villaverde, S."

Now showing 1 - 2 of 2

Physiological and chemical gradients in a pseudomonas putida 54g biofilm degrading toluene in a flat plate vapor phase bioreactor
(1997-11) Villaverde, S.; Mirpuri, Rajesh G.; Lewandowski, Zbigniew; Jones, Warren L.
A Pseudomonas putida 54G biofilm was grown on toluene vapor supplied as the sole external carbon and energy source in a flat plate biofilm reactor. Enumerations of cells in the biofilm were made using culture techniques (selective and nonselective for toluene) and microscopic techniques (total and respiring cells), and an analysis of the progression of the state of the culture was made by examination of various fractions of the populations. Long-term exposure to higher levels of toluene produced the following trends: (i) lower fraction of total cells that respired; (ii) lower fraction of culturable cells that also grew on toluene; (iii) higher fraction of respiring cells that could not grow on toluene plates; and (iv) a relatively constant fraction of total cells that could not be cultured on toluene. Respiration rate was determined using oxygen microsensors, and the fraction of the total respiration that was not associated with toluene uptake increased with higher toluene exposure. A combination of cryosectioning and respiration rate data was used to demonstrate that more respiring cells and a higher respiration rate both occurred at the base of the film, suggesting a deterioration in physiological state with continued exposure to toluene. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng56: 361–371, 1997.
Study of toluene degradation kinetics in a flat plate vapor phase bioreactor using oxygen microsensors
(1997) Villaverde, S.; Mirpuri, Rajesh G.; Lewandowski, Zbigniew; Jones, Warren L.
The paper describes the toluene degradation process in a flat plate vapor phase bioreactor (VPBR) by a Pseudomonas putida 54G biofilm. Oxygen microelectrodes were used to measure oxygen concentration profiles through the gas, liquid, and biofilm phases. The linear shape of the dissolved oxygen concentration profile in the outer 87% of the biofilm thickness suggested an absence of reaction in this layer. Oxygen consumption in the remaining basal 13 % (0.3 mm) followed zero order kinetics with a rate constant of 102.2 g m−3 h−1, for toluene gas concentration of 1.5 g m−3. The increase in respiratory activity near the substratum was confirmed by microscopic study of cryogenic biofilm sections, and the lack of activity in the surface film was interpreted as a consequence of injury exerted by the toxic substrate. The accumulation of dead cells on the top of the biofilm contributed a resistance to the transport of substrates to deeper layers of the biofilm suggesting a protective role of the outer layer against the harmful effect of the toxic. These results highlight a new conceptual biofilm model in which both microbial growth and inactivation are controlled by substrate transport, leading to a structure that itself controls substrate availability.