The colorimetric assay of viability for algae (CAVA): a fast and accurate technique

International audienceDetermining the fraction of viable cells in algal cultures is critical to improve the understanding and control of algal microbiology, ecology, and biotechnology. Whereas current techniques for algal viability determination can be rather cumbersome, this paper describes a new assay that enables the rapid quantification of algal viability using only spectrophotometric measurements. This technique, henceforth named CAVA test, relies on the selective adsorption of erythrosine by non-viable cells and was validated on the algal species Chlamydomonas reinhardtii and Chlorella vulgaris. The results obtained by the CAVA test were in good agreement with the in situ measurement of oxygen production rates. In addition, the CAVA test was shown to quantify the viability of algal samples regardless of the cause of death (heating, UV-irradiation or H2O2 exposure). The CAVA technique has28 therefore the potential to offer fast and universal approach to measure the viability of algal samples

Good science for improving policy: greenhouse gas emissions from agricultural manures

Australia’s and New Zealand’s major agricultural manure management emission sources are reported to be, in descending order of magnitude: (1) methane (CH4) from dairy farms in both countries; (2) CH4 from pig farms in Australia; and nitrous oxide (N2O) from (3) beef feedlots and (4) poultry sheds in Australia. We used literature to critically review these inventory estimates. Alarmingly for dairy farm CH4 (1), our review revealed assumptions and omissions that when addressed could dramatically increase this emission estimate. The estimate of CH4 from Australian pig farms (2) appears to be accurate, according to industry data and field measurements. The N2O emission estimates for beef feedlots (3) and poultry sheds (4) are based on northern hemisphere default factors whose appropriateness for Australia is questionable and unverified. Therefore, most of Australasia’s key livestock manure management greenhouse gas (GHG) emission profiles are either questionable or are unsubstantiated by region-specific research. Encouragingly, GHG from dairy shed manure are relatively easy to mitigate because they are a point source which can be managed by several ‘close-to-market’ abatement solutions. Reducing these manure emissions therefore constitutes an opportunity for meaningful action sooner compared with the more difficult-to-implement and long-term strategies that currently dominate agricultural GHG mitigation research. At an international level, our review highlights the critical need to carefully reassess GHG emission profiles, particularly if such assessments have not been made since the compilation of original inventories. Failure to act in this regard presents the very real risk of missing the ‘low hanging fruit’ in the rush towards a meaningful response to climate chang

Good science for improving policy: greenhouse gas emissions from agricultural manures

Australia’s and New Zealand’s major agricultural manure management emission sources are reported to be, in descending order of magnitude: (1) methane (CH4) from dairy farms in both countries; (2) CH4 from pig farms in Australia; and nitrous oxide (N2O) from (3) beef feedlots and (4) poultry sheds in Australia. We used literature to critically review these inventory estimates. Alarmingly for dairy farm CH4 (1), our review revealed assumptions and omissions that when addressed could dramatically increase this emission estimate. The estimate of CH4 from Australian pig farms (2) appears to be accurate, according to industry data and field measurements. The N2O emission estimates for beef feedlots (3) and poultry sheds (4) are based on northern hemisphere default factors whose appropriateness for Australia is questionable and unverified. Therefore, most of Australasia’s key livestock manure management greenhouse gas (GHG) emission profiles are either questionable or are unsubstantiated by region-specific research. Encouragingly, GHG from dairy shed manure are relatively easy to mitigate because they are a point source which can be managed by several ‘close-to-market’ abatement solutions. Reducing these manure emissions therefore constitutes an opportunity for meaningful action sooner compared with the more difficult-to-implement and long-term strategies that currently dominate agricultural GHG mitigation research. At an international level, our review highlights the critical need to carefully reassess GHG emission profiles, particularly if such assessments have not been made since the compilation of original inventories. Failure to act in this regard presents the very real risk of missing the ‘low hanging fruit’ in the rush towards a meaningful response to climate chang

Photodegradation and sorption govern tetracycline removal during wastewater treatment in algal ponds

Producción CientíficaThe degradation of the antibiotic tetracycline, supplied at 100 µg L−1 in domestic wastewater, was studied in an outdoor, pilot scale, high rate algal pond (HRAP). Effective operation was demonstrated with the biomass concentration and the chemical oxygen demand removal efficiency averaging 1.2 ± 0.1 gTSS L−1 and 80 ± 4%, respectively, across all operational periods. Tetracycline removal exceeded 93% and 99% when the HRAP was operated at hydraulic retention times of 4 and 7 days, respectively. Batch tests and pulse testing during HRAP operation repeatedly evidenced the significance of photodegradation as a removal mechanism. Sorption dominated tetracycline removal during the night, but accounted for less than 6% of the total pollutant removal based on sorbed tetracycline extracted from biomass. Overall, these results provide the first demonstration of efficient antibiotic removal, occurring mainly via indirect photodegradation, during relevant HRAP operation (low pollutant concentration, domestic wastewater and natural sunlight).Ministerio de Economía, Industria y Competitividad (Project CTM2015-70442-R and Red NOVEDAR

Chlamydomonas reinhardtii, an Algal Model in the Nitrogen Cycle

Nitrogen (N) is an essential constituent of all living organisms and the main limiting macronutrient. Even when dinitrogen gas is the most abundant form of N, it can only be used by fixing bacteria but is inaccessible to most organisms, algae among them. Algae preferentially use ammonium (NH4+) and nitrate (NO3−) for growth, and the reactions for their conversion into amino acids (N assimilation) constitute an important part of the nitrogen cycle by primary producers. Recently, it was claimed that algae are also involved in denitrification, because of the production of nitric oxide (NO), a signal molecule, which is also a substrate of NO reductases to produce nitrous oxide (N2O), a potent greenhouse gas. This review is focused on the microalga Chlamydomonas reinhardtii as an algal model and its participation in different reactions of the N cycle. Emphasis will be paid to new actors, such as putative genes involved in NO and N2O production and their occurrence in other algae genomes. Furthermore, algae/bacteria mutualism will be considered in terms of expanding the N cycle to ammonification and N fixation, which are based on the exchange of carbon and nitrogen between the two organisms

Innovative Bioreactors for the Degradation of Polycyclic Aromatic Hydrocarbons

The development of biological reactors for the treatment of toxic and recalcitrant organic pollutants is a complex task. Firstly, microbial inoculation, acclimation and selection must be optimized to provide the best microflora possible. Secondly, innovative technologies must be developed to overcome the intrinsic low degradation rates of hardly-degradable pollutants in order to allow short treatment times. Finally, since the pollutants involved are often toxic, it is also important to use well-managed treatment system that limit potential process hazards. Efficient inoculum was provided by using a mixture of indigenous soil microflora, most likely containing contaminant-degrading species, and activated sludge sample to provide microbial diversity as a protection against metabolite accumulation and substrate inhibition effects. Both fed-batch and continuous cultivations were suitable for microbial selection. Since the selection of degrading species depends on the origin of the inoculum and the procedure and system used, inoculation, acclimation and selection should be performed each time the treatment of a new effluent or the performance of a new process is studied. Both Suspended-Carrier and Packed-Bed reactors allowed the fast treatment of diluted contaminated effluent. The packed-bed reactor was preferred since it favored the development of very diverse microflora and was based on the use of a cheaper carrier. Special care should be taken in controlling pollutant adsorption to the carriers. Biphasic reactors were found to be suitable for the treatment of concentrated mixtures of contaminants such as soil extracts. Besides reducing the aqueous toxicity of the contaminants, the use of an organic phase in biphasic reactor advantageously permitted to avoid pollutant volatilization and adsorption. However, their large-scale application remains dependent on several improvements. The potential of algae photosynthesis to produce oxygen in-situ in the reactor, which limits the risk for pollutant volatilization, was clearly demonstrated. Emphasis should be given on optimizing photosynthesis efficiency, which depends on the light intensity and the algal population size, rather that the degradation of the pollutants. Since recording pollutant disappearance does not inform about the mechanism of removal and the pollutants involved are toxic, it is very important to monitor microbial activity during the entire process. The rate of disappearance of the electron acceptor used by the microflora could often be well correlated with the microbial activity and the pollutant biodegradation rate. This could lead to the development of biosensors and monitoring strategies suitable for the biological treatment of toxic and recalcitrant pollutants. Finally, although it was often difficult to avoid abiotic removal mechanisms and to monitor microbial degradation, it was still possible to evaluate and control these phenomena in most of the systems described in this thesis work. This clearly demonstrates a very important advantage of ex-situ remediation processes compared to in-situ processes

Development of water quality test kit based on substrate utilization and toxicity resistance in river microbial communities

Methods for measuring toxicity or respiratory activity of microbial cultures can be used as tools for assessing the presence of chemicals and their impact on the streams. The proposed toxicity test is based on the respirometric characteristics of the bacteria according to the principals of Biolog's microplate system. As the microorganism are utilizing the carbon source (peptone), the reduction of the tetrazolium dye as the redox indicator is taking place, leading to a developing change in the well's color The tests provided us with information in regard to the toxicity range of the chemicals with activated sludge and Alcaligenes

Metabolically versatile large-genome prokaryotes

Although versatile microorganisms are critical in industrial applications where the ability to cope with change and carry out complex tasks is needed, very little is in fact known about the evolutionary and ecological meanings of versatility in prokaryotes. Testing the hypothesis that a large genome size is a prerequisite for versatility in prokaryotes, we found that putatively versatile prokaryotes are phylogenetically and ecologically diverse and indeed include many well known and commercially relevant versatile microorganisms. Despite individual differences in metabolic abilities, a common trait of large-genome prokaryotes appears that they have gained their large genomes as an evolutionary response to nutrient-scarce and/or variable environments. This insight seriously questions the ability of traditional microbiology methods to isolate versatile prokaryotes and casts doubt on the ecological relevance of knowledge based on the study of specialists

Sequential UV-biological degradation of polycyclic aromatic hydrocarbons in two-phases partitioning bioreactors

A method based on U-V-irradiation in organic solvent followed by transfer of the remaining pollutants into silicone oil for subsequent biodegradation in a biphasic system inoculated with a phenanthrene degrading Pseudomonas sp. was tested for the treatment of various mixtures of PAHs. Acetone was first selected as the most suitable solvent compared to methanol, acetonitrile and silicone oil for the removal of pyrene and phenanthrene. The sequential treatment was then applied to the treatment of a mixture of fluorene, phenanthrene, anthracene, fluoranthrene, pyrene, benzo(a)anthracene and benzo(a)pyrene in acetone. These compounds were photodegraded in the following order of initial removal rates (mg l(-1) d(-1)): benzo(a)pyrene (7.8) > anthracene (5.0) > benzo(a)anthracene (2.5) > fluoranthrene (1.8) > pyrene (1.5) > phenanthrene (1.2) > fluorene (0.2). U-V-treatment allowed complete removal of, anthracene, benzo(a)anthracene and benzo(a)pyrene and removals of 63% of pyrene and 37% of fluorene after 434h or irradiation. The subsequent biological treatment removed the remaining phenanthrene and fluorene by 100% and 90%, respectively, after 790h of cultivation. Although less efficient due to the presence of interfering compounds, the UV-biological treatment of a soil extract allowed a 63% removal of the seven PAHs named above. Microbial growth did not occur when the pollutants were directly supplied to the microorganism showing that biphasic systems reduced the toxicity effects cause by mixtures of PAHs at high concentrations. This study demonstrates the potential of selective UV treatment of high molecular weight PAHs followed by biological treatment of the low molecular weight species in biphasic systems. (c) 2004 Elsevier Ltd. All rights reserved