Biomedical subjects

Maria A M Reis

Publications and source records attributed to Maria A M Reis.

11 recordsLinked to original sources

PubMed2006

Recent advances in polyhydroxyalkanoate production by mixed aerobic cultures: from the substrate to the final product.

Numerous bacteria have been found to exhibit the capacity for intracellular polyhydroxyalkanoates (PHA) accumulation. Current methods for PHA production at the industrial scale are based on their synthesis from microbial isolates in either their wild form or by recombinant strains. High production costs are associated with these methods; thus, attempts have been made to develop more cost-effective processes. Reducing the cost of the carbon substrates (e.g., through feeding renewable wastes) and increasing the efficiency of production technologies (including both fermentation and downstream extraction and recovery) are two such examples of these attempts. PHA production processes based on mixed microbial cultures are being investigated as a possible technology to decrease production costs, since no sterilization is required and bacteria can adapt quite well to the complex substrates that may be present in waste material. PHA accumulation by mixed cultures has been found under various operational conditions and configurations at both bench-scale and full-scale production. The process known as "feast and famine" or as "aerobic dynamic feeding" seems to have a high potential for PHA production by mixed cultures. Enriched cultures submitted to a transient carbon supply can synthesize PHA at levels comparable to those of pure cultures. Indeed, the intracellular PHA content can reach around 70% of the cell dry weight, suggesting that this process could be competitive with pure culture PHA production when fully developed. Basic and applied research of the PHA production process by mixed cultures has been carried out in the past decade, focusing on areas such as microbial characterization, process configuration, reactor operational strategies, process modeling and control, and polymer characterization. This paper presents a review of the PHA production process with mixed cultures, encompassing the findings reported in the literature as well as our own experimental results in relation to each of these areas.

Bacteria, Aerobic↗

PubMed2005

Effect of operating parameters on molinate biodegradation.

The effect of operating conditions during molinate degradation by the defined mixed bacterial culture DC, previously described as able to mineralize molinate, was evaluated in a batch reactor. Parameters such as the rate of molinate degradation, the dissolved organic carbon (DOC) consumption and the accumulation of molinate degradation products were monitored along the culture growth. The effect of conditions such as temperature, pH, aeration rate, salinity, and presence of additional carbon and/or nitrogen sources, was tested independently. Degradation of molinate in river water was also evaluated. Culture DC was able to grow and to mineralize molinate at all the conditions assayed. Temperature was the factor with the strongest influence on bacterial growth and molinate mineralization. The lowest and the highest rate values of growth (0.010 and 0.110 h(-1)) and of molinate degradation (0.027 and 0.180 g molinate g(-1)celldrywth(-1)) were obtained at 15 and 35 degrees C, respectively. In cultures with approximately 187 mgl(-1) of molinate, 2-oxo-molinate was the major molinate degradation product accumulated in the medium, in concentrations below 0.133 mgl(-1). Degradation of molinate was also evaluated in a continuous stirred tank reactor (CSTR). Operating the CSTR at a hydraulic retention time (HRT) of 83 h, fed with medium containing molinate concentrations ranging from 1 to 3mM, culture DC degraded the herbicide with specific degradation rates similar to those obtained in the batch systems.

Azepines↗

PubMed2005

Simultaneous removal of perchlorate and nitrate from drinking water using the ion exchange membrane bioreactor concept.

This work evaluates the feasibility of the ion exchange membrane bioreactor (IEMB) concept for the simultaneous removal of perchlorate and nitrate from drinking water, when nitrate is present in the ppm range and perchlorate in the ppb range. The IEMB concept combines Donnan dialysis and simultaneous biological degradation of both pollutants. Membrane transport studies showed that Donnan dialysis is suitable for obtaining water with concentrations of perchlorate and nitrate below the recommended levels. However, the pollutants were accumulated in a receiving stream, thus requiring additional treatment before disposal. On the other hand, the IEMB process operated with hydraulic retention times ranging from 1.4 to 8.3h in the water compartment, proved to remove effectively perchlorate and nitrate while preserving the water composition with respect to other ions, thus avoiding secondary contamination of the treated water. For a polluted water stream containing 100 ppb of ClO(4)(-) and 60 ppm of NO(3)(-), the concentrations of both ions in the treated stream were kept below the recommended levels of 4 ppb for ClO(4)(-) and 25 ppm for NO(3)(-). The IEMB system was operated under ethanol limitation, but even under these conditions, an increase of the perchlorate and nitrate concentrations in the treated water was not observed for up to 6 days.

Bioreactors↗

PubMed2005

Microbial population response to changes of the operating conditions in a dynamic nutrient-removal sequencing batch reactor.

A nutrient-removal sequencing batch reactor operated with short anaerobic/aerobic cycles was subjected to different operating conditions, namely, cycle length, feeding pattern and feed composition. The changes in microbial population, as well as the contribution of microbial groups to the total nutrient removal, were estimated using the kinetic parameters obtained in this study. Denitrifying polyphosphate-accumulating organisms (DPAOs) were detected in the system, representing a fraction of 23% of phosphorus-accumulating organisms (PAOs). The results suggest that DPAOs and non-DPAOs are different microorganisms. The presence of nitrate in the feed stimulated DPAOs to predominate over non-DPAOs. Feeding the reactor with a mixture of organic substrates also stimulated DPAOs. Glycogen-accumulating organisms (GAOs) were likely to be present in the system and their development over PAOs was apparently favoured by increasing the aeration time and feeding during the aerobic phase. In contrast, the presence of propanoate in the feed apparently favoured PAOs over GAOs.

Aerobiosis↗

PubMed2005

Synthesis of polyhydroxyalkanoates from different short-chain fatty acids by mixed cultures submitted to aerobic dynamic feeding.

The production of polyhydroxyalkanoates from acetate and propionate by two mixed cultures well adapted to each of these substrates was evaluated. Sludge fed with acetate (A), produced a homopolymer of hydroxybutyrate (HB), whereas sludge fed with propionate (P) produced a copolymer of HB and HV (hydoxyvalerate). Switching the substrate feeds, propionate to sludge A and acetate to culture P, a terpolymer of HB, HV and hydroxymethylvalerate (HMV) was obtained with culture A and a copolymer of P(HB/HV) by sludge P. Regardless of the population used, the polymer yield and productivity were much higher for acetate than for propionate. Feeding a mixture of acetate and propionate, in equal parts, to both cultures resulted in an increase of HV units produced per C mol of propionate consumed, relative to the situation where only propionate was used. The individual use of butyrate and valerate by culture A was also studied. Butyrate produced a homopolymer whereas valerate was stored as a terpolymer of P(HB/HV/HMV). The polymer yields on acetate and butyrate were higher than those on propionate and valerate. The polymer productivity was higher for acetate and propionate than for butyrate and valerate. Results showed that the polymer composition, and consequently the polymer properties, could be manipulated by varying the volatile fatty acid feed composition and/or the population.

Acetic Acid↗

PubMed2005

Mathematical modelling of a mixed culture cultivation process for the production of polyhydroxybutyrate.

Mixed cultures submitted to acetate "feast" and "famine" cycles are able to store intracellularly high quantities of polyhydroxybutyrate (PHB). It was demonstrated in a previous study that the intracellular PHB content can be increased up to 78.5% (g HB/gVSS) of cell dry weight in a sequencing batch reactor (SBR) with optimised operating conditions. The specific PHB formation rate was also shown to be higher for mixed cultures than for pure cultures. Such high intracellular PHB contents and specific productivity open new perspectives for the industrial production of polyhydroxyalkanoates (PHA) using mixed cultures instead of pure cultures. The main goal in this work was to develop a mathematical model of mixed cultures envisaging the optimisation of PHB production. A relatively simple two-compartments cell model was developed based on experimental observations and other models proposed in the literature. A convenient experimental planing allowed to identify the kinetic parameters and yield coefficients. Experiments were performed with and without ammonia limitation enabling the analysis of PHB formation independently of the cell growth process. The experimental true yields partially confirm the theoretical values proposed in the literature. The final model exhibited high accuracy in describing the process state of most experiments performed, thus opening good perspectives for future model-based optimisation studies.

Bacteria↗

PubMed2005

Non-mechanistic modelling of complex biofilm reactors and the role of process operation history.

Using the example of a membrane-supported biofilm reactor for industrial effluent treatment, different non-mechanistic approaches for the modelling of complex bioprocesses are presented and evaluated. The models were obtained employing feedforward artificial neural network analysis for the association of process operation with process performance. Three modelling approaches are discussed, i.e. autonomous static (AS) modelling, non-autonomous static (NAS) modelling, as well as a novel approach termed dynamic modelling with embedding of artificial neural network inputs. They are compared with regard to their ability to infer process performance for two different pollutant case studies, employing 1,2-dichloroethane and 3-chloro-4-methylaniline, respectively. The suitability of the different approaches was found to be strongly dependent on process configuration. Especially in configurations where lag times are apparent, the dynamic modelling approach was found to be superior, and process performance prediction was found to be strongly dependent on the history of process operation.

Algorithms↗

PubMed2004

Optimization of polyhydroxybutyrate production by mixed cultures submitted to aerobic dynamic feeding conditions.

Activated sludge submitted to aerobic dynamic feeding conditions showed a good and stable capacity to store polyhydroxybutyrate (PHB). The system, working for 2 years, selected a microbial population with a high PHB storage capacity. The influence of carbon and nitrogen concentrations on the PHB accumulation yield was studied in a range of 15-180 Cmmol/l for acetate and 0-2.8 Nmmol/l for ammonia. Low ammonia concentrations favored PHB accumulation. The maximum PHB content, 67.5%, was obtained for 180 Cmmol/l of acetate supplied in one pulse. However, such high substrate concentration proved to be inhibitory for the storage mechanism, causing a slowdown of the specific PHB storage rate. In order to avoid substrate inhibition, 180 Cmmol/l of acetate was supplied in different ways: continuously fed and in three pulses of 60 Cmmol/l each. In both cases the specific PHB storage rate increased and the PHB content obtained were 56.2% and 78.5%, respectively. The latter value of PHB content is similar to that obtained by pure cultures and was never reported for mixed cultures. Addition of acetate by pulses controlled by the oxygen concentration was kept for 16 days, the PHB content being always above 70% of cell dry weight.

Acetates↗

PubMed2003

Metabolic pathway for propionate utilization by phosphorus-accumulating organisms in activated sludge: 13C labeling and in vivo nuclear magnetic resonance.

In vivo 13C and 31P nuclear magnetic resonance techniques were used to study propionate metabolism by activated sludge in enhanced biological phosphorus removal systems. The fate of label supplied in [3-13C]propionate was monitored in living cells subjected to anaerobic/aerobic cycles. During the anaerobic phase, propionate was converted to polyhydroxyalkanoates (PHA) with the following monomer composition: hydroxyvalerate, 74.2%; hydroxymethylvalerate, 16.9%; hydroxymethylbutyrate, 8.6%; and hydroxybutyrate, 0.3%. The isotopic enrichment in the different carbon atoms of hydroxyvalerate (HV) produced during the first anaerobic stage was determined: HV5, 59%; HV4, 5.0%; HV3, 1.1%; HV2, 3.5%; and HV1, 2.8%. A large proportion of the supplied label ended up on carbon C-5 of HV, directly derived from the pool of propionyl-coenzyme A (CoA), which is primarily labeled on C-3; useful information on the nature of operating metabolic pathways was provided by the extent of labeling on C-1, C-2, and C-4. The labeling pattern on C-1 and C-2 was explained by the conversion of propionyl-CoA to acetyl-CoA via succinyl-CoA and the left branch of the tricarboxylic acid cycle, which involves scrambling of label between the inner carbons of succinate. This constitutes solid evidence for the operation of succinate dehydrogenase under anaerobic conditions. The labeling in HV4 is explained by backflux from succinate to propionyl-CoA. The involvement of glycogen in the metabolism of propionate was also demonstrated; moreover, it was shown that the acetyl moiety to the synthesis of PHA was derived preferentially from glycogen. According to the proposed metabolic scheme, the decarboxylation of pyruvate is coupled to the production of hydrogen, and the missing reducing equivalents should be derived from a source other than glycogen metabolism.

Aerobiosis↗

PubMed2002

Methods for detection and visualization of intracellular polymers stored by polyphosphate-accumulating microorganisms.

Polyphosphate-accumulating microorganisms (PAOs) are important in enhanced biological phosphorus (P) removal. Considerable effort has been devoted to understanding the biochemical nature of enhanced biological phosphorus removal (EBPR) and it has been shown that intracellular polymer storage plays an important role in PAO's metabolism. The storage capacity of PAOs gives them a competitive advantage over other microorganisms present that are not able to accumulate internal reserves. Intracellular polymers stored by PAOs include polyphosphate (poly-P), polyhydroxyalkanoates (PHAs) and glycogen. Staining procedures for qualitative visualization of polymers by optical microscopy and combinations of these procedures with molecular tools for in situ identification are described here. The strengths and weaknesses of widely used polymer quantification methods that require destruction of samples, are also discussed. Finally, the potential of in vivo nuclear magnetic resonance (NMR) spectroscopy for on-line measurement of intracellular reserves is reported.

Bacteria, Aerobic↗

PubMed2002

Analysis of the microbial community structure and function of a laboratory scale enhanced biological phosphorus removal reactor.

A laboratory scale sequencing batch reactor (SBR) operating for enhanced biological phosphorus removal (EBPR) and fed with a mixture of volatile fatty acids (VFAs) showed stable and efficient EBPR capacity over a four-year-period. Phosphorus (P), poly-beta-hydroxyalkanoate (PHA) and glycogen cycling consistent with classical anaerobic/aerobic EBPR were demonstrated with the order of anaerobic VFA uptake being propionate, acetate then butyrate. The SBR was operated without pH control and 63.67 +/- 13.86 mg P l-1 was released anaerobically. The P% of the sludge fluctuated between 6% and 10% over the operating period (average of 8.04 +/- 1.31%). Four main morphological types of floc-forming bacteria were observed in the sludge during one year of in-tensive microscopic observation. Two of them were mainly responsible for anaerobic/aerobic P and PHA transformations. Fluorescence in situ hybridization (FISH) and post-FISH chemical staining for intracellular polyphosphate and PHA were used to determine that 'Candidatus Accumulibacter phosphatis' was the most abundant polyphosphate accumulating organism (PAO), forming large clusters of coccobacilli (1.0-1.5 micro m) and comprising 53% of the sludge bacteria. Also by these methods, large coccobacillus-shaped gammaproteobacteria (2.5-3.5 micro m) from a recently described novel cluster were glycogen-accumulating organisms (GAOs) comprising 13% of the bacteria. Tetrad-forming organisms (TFOs) consistent with the 'G bacterium' morphotype were alphaproteobacteria, but not Amaricoccus spp., and comprised 25% of all bacteria. According to chemical staining, TFOs were occasionally able to store PHA anaerobically and utilize it aerobically.

Bacteria, Anaerobic↗