Characterization of hydrocarbons degradation by Alcanivorax venustensis lyophilized biomass entrapped in hydrogel support

New Biotechnology · Volume 25S · September 2009

as aerobic dynamic feeding (ADF) seems to have the highest potential for PHA synthesis by mixed cultures. In ADF system, selection of microorganisms toward obtaining homogenous population with a high and stable capacity of PHA accumulation is based on biomass exposition to consecutive periods of external substrate accessibility and unavailability. Enriched cultures are then exploited with an excess of external substrate concentration at the separated accumulation stage to maximize the PHA cell content. In present study, it was assumed that selection of culture with a high PHA storage capacity could be obtained by employing reactor feeding continuously with substrate and altering in time of ammonia availability. The experiments were performed in sequencing batch reactor (SBR) using crude glycerol as a carbon source and applying two types of fermentation. In fermentation 1, the SBR was operated under ADF conditions. The PHA synthesis was stimulated by keeping gradient of substrate concentration during the SBR cycle, by adding carbon source to the reactor in one-pulse at the beginning of the cycle. Organic load rate (OLR) amounted to 3.70 g COD/L d. In fermentation 2, PHA accumulation was favored by dividing the SBR cycle into three phases: 1 (biomass growth), 2 (PHA synthesis under ammonia limited conditions) and 3 (PHA consumption), which was attained by continuous feeding of culture medium with distinct chemical constitution. The OLR was 3.18 g COD/L d. Continuous substrate feeding and periodic ceasing of ammonia supplying were favorable as regards process efficiency and type of PHA storage. Under ADF conditions, the highest PHA biomass content (ηPHA ), observed biomass yield coefficient (Yobs ), observed PHA yield coefficient (Yobs,PHA ) and volumetric productivity amounted to 47.6 ± 1.7% d.w., 0.26 ± 0.08 g d.w./g COD, 0.10 ± 0.02 g PHA/g COD and 350 ± 32.2 mg PHA/L d, respectively. The microorganisms accumulated mainly homopolymer 3hydroxybutyric acid (3HB). The concentration of 3-hydroxyvaleric acid (3HV) did not exceed 6%. In ammonia limited fermentation, the values of ηPHA , Yobs and Yobs,PHA were 40.5 ± 6.9% d.w., 0.60 ± 0.09 g d.w./g COD and 0.25 ± 0.05 g PHA/g COD, respectively. Polymer with 45% of 3HV content was synthesized. Volumetric productivity (595.1 ± 127.4 mg PHA/L d) was approximately twofold higher than in ADF system. doi:10.1016/j.nbt.2009.06.580

3.1.36 Characterization of hydrocarbons degradation by Alcanivorax venustensis lyophilized biomass entrapped in hydrogel support E. Largo 1,∗ , M. Buxens 1 , E. Díaz De Apodaca 2 , N. Sagarminaga 2 , J.R. Ochoa 2 , J.L. Serra 1 , M.J. Llama 1 1

2

University of the Basque Country, Leioa, Spain LEIA, Technological Development Centre, Spain

Petroleum and its products are major pollutants of marine environments and shorelines. In situ bioremediation, using microorganisms capable to degrade this kind of compounds, could be an interesting strategy to depollute rocky seaside places. The use of free bacterial biomass presents low effectiveness than the S260

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immobilized counterpart, because of the fact that the tides scatter and sweep away the applied microorganisms. To minimize the wash-out of sea water, Alcanivorax venustensis cells have been immobilized in a polymeric, adhesive and biodegradable hydrogel support. Furthermore, cell immobilization protects microorganisms against changes of temperature, improves the survival of cells, and makes possible to put them in contact with the pollutant for a more prolonged period. An experimental lab-bench system, which mimics the adhesion to the rocks, the damp atmosphere of the seaside places, and the presence of pollutants, has been designed. The potential of immobilized hydrocarbon-degrading bacterial cells to bioremediate oil polluted surfaces was evaluated in this experimental system. The degradation time-course of mineral oil, used as a hydrocarbon standard, has been assessed by GC/MS. To improve and simplify the immobilization process, lyophilized biomass and hydrogel have been used, and the efficiency of the system has been compared with that of immobilized fresh cells from suspension cultures. Moreover, the effects of some variables such as temperature, salinity, nitrogen source availability and amount of biomass in the mineral oil degradation, have been assessed. Effect of time and volume of lyophilized biomass as well as hydrogel rehydration degree have been also evaluated. Results show an elevate rate of microbial degradation of mineral oil in two days. doi:10.1016/j.nbt.2009.06.581

3.1.37 Response surface optimization of enzymatic hydrolysis of Cytisus striatus for bioethanol production S. Ferreira 1,∗ , A.P. Duarte 1 , M.H.L. Ribeiro 2 , J.A. Queiroz 1 , F.C. Domingues 1 1

2

Universidade da Beira Interior, Covilhã, Portugal Universidade de Lisboa, Lisboa, Portugal

Current ethanol production processes using crops such as sugar cane and corn are well-established; however, employment of a cheaper substrate such as lignocellulose could make bioethanol more cost-competitive with fossil fuels, without having the ethical concerns associated with the use of potential food resources. The Portuguese forest occupies 3.4 million hectares that is 38.4% of the territory, and can be seen as a source of large amounts of forestry biomass residues, including shrubs, such as broom (Cytisus striatus) that is considered in many regions as an invasive plant. The sequential configuration employed to obtain cellulosic ethanol implies that the solid fraction of pretreated lignocellulosic material undergoes hydrolysis. Considering this, the enzymatic hydrolysis of pretreated Cytisus striatus was studied following an experimental design as a statistical problem solving approach. Plackett-Burman design was used to select the most important variables from the simultaneous study on influence of operating and reactional conditions, and Central Composite Rotatable Design to optimize the process of enzymatic hydrolysis. The optimization of enzymatic hydrolysis using the response surface methodology allowed to study the influence of pH, temperature, cellulases concentration, poly(ethylene)glycol 4000 (PEG 4000) concentration and incubation time on the production of