Elemental analysis for biomass determination in the presence of insoluble substrates

Biological treatment of wastewater polluted with an oxyfluorfen-based commercial herbicide

Fluoxil-24 is a commercial herbicide based on oxyfluorfen (a hazardous non-soluble organochlorinated compound) and additional compounds used as solvents. The aim of this work is to study the biotreatability of this commercial herbicide in water through batch experiments performed at different temperatures (15, 20, 25 and 30 °C) and initial concentrations (85, 150, 300 and 500 mg L^-1 of oxyfluorfen). Activated sludge from an oil refinery wastewater treatment plant was acclimated and used for biodegradation experiments. Two main mechanisms, volatilization and biodegradation, were observed to be responsible of the herbicide removal. Fluoxil-24 removal efficiencies between approximately 40% and 80% were reached after 70 h, depending on the conditions used, and oxyfluorfen was not completely removed. Regarding the influence of the temperature, thermal inhibition problems appeared at 30 °C, and the volatilization rate of solvents increased, causing oxyfluorfen to become unavailable for microorganisms. An increase of herbicide initial concentration did not clearly affect the herbicide removal efficiency, whereas it negatively affected the biological mechanism. The experimental results were fitted to a mathematical model that included both simultaneous mechanisms of volatilization and Monod biodegradation kinetics. The model was able to predict the experimental results, and the calculated model parameters confirmed the effect of the variables under study.

Modelling aerobic biodegradation of atrazine and 2,4-dichlorophenoxy acetic acid by mixed-cultures

The aim of this work was to study and to model the biodegradation of atrazine and 2,4-dichlorophenoxy acetic acid by aerobic mixed cultures. Slow removal rates were observed when biodegrading atrazine, in spite of the initial concentrations. However, high removal rates were obtained when biodegrading 2,4-D, removing up to 100mg/L in about 2months. Regarding the 2,4-D it must be highlighted that a lag phase appears, being its length proportional to the initial 2,4-D concentration. The biodegradation trends were fitted to a Monod based model and the value of the main parameters determined. In the case of atrazine they were µ_max: 0.011 1/d and Y: 0.53g/g and in the case of 2,4-D µ_max: 0.071 1/d and Y: 0.44g/g, indicating the higher persistence of atrazine. Once finished the experiments the microbial population was characterized being the major genus Pseudomonas when treating atrazine and Rhodococcus when treating 2,4-D.

Growth of iron(III)-reducing bacteria on clay minerals as the sole electron acceptor and comparison of growth yields on a variety of oxidized iron forms

Smectite clay minerals are abundant in soils and sediments worldwide and are typically rich in Fe. While recent investigations have shown that the structural Fe(III) bound in clay minerals is reduced by microorganisms, previous studies have not tested growth with clay minerals as the sole electron acceptor. Here we have demonstrated that a pure culture of Shewanella oneidensis strain MR-1 as well as enrichment cultures of Fe(III)-reducing bacteria from rice paddy soil and subsurface sediments are capable of conserving energy for growth with the structural Fe(III) bound in smectite clay as the sole electron acceptor. Pure cultures of S. oneidensis were used for more detailed growth rate and yield experiments on various solid- and soluble-phase electron acceptors [smectite, Fe(III) oxyhydroxide FeOOH, Fe(III) citrate, and oxygen] in the same minimal medium. Growth was assessed as direct cell counts or as an increase in cell carbon (measured as particulate organic carbon). Cell counts showed that similar growth of S. oneidensis (10(8) cells ml(-1)) occurred with smectitic Fe(III) and on other Fe forms [amorphous Fe(III) oxyhydroxide, and Fe citrate] or oxygen as the electron acceptor. In contrast, cell yields of S. oneidensis measured as the increase in cell carbon were similar on all Fe forms tested while yields on oxygen were five times higher, in agreement with thermodynamic predictions. Over a range of particle loadings (0.5 to 4 g liter(-1)), the increase in cell number was highly correlated to the amount of structural Fe in smectite reduced. From phylogenetic analysis of the complete 16S rRNA gene sequences, a predominance of clones retrieved from the clay mineral-reducing enrichment cultures were most closely related to the low-G+C gram-positive members of the Bacteria (Clostridium and Desulfitobacterium) and the delta-Proteobacteria (members of the Geobacteraceae). Results indicate that growth with smectitic Fe(III) is similar in magnitude to that with Fe(III) oxide minerals and is dependent upon the mineral surface area available. Iron(III) bound in clay minerals should be considered an important electron acceptor supporting the growth of bacteria in soils or sedimentary environments.

Cave biosignature suites: microbes, minerals, and Mars

Earth's subsurface offers one of the best possible sites to search for microbial life and the characteristic lithologies that life leaves behind. The subterrain may be equally valuable for astrobiology. Where surface conditions are particularly hostile, like on Mars, the subsurface may offer the only habitat for extant lifeforms and access to recognizable biosignatures. We have identified numerous unequivocally biogenic macroscopic, microscopic, and chemical/geochemical cave biosignatures. However, to be especially useful for astrobiology, we are looking for suites of characteristics. Ideally, "biosignature suites" should be both macroscopically and microscopically detectable, independently verifiable by nonmorphological means, and as independent as possible of specific details of life chemistries--demanding (and sometimes conflicting) criteria. Working in fragile, legally protected environments, we developed noninvasive and minimal impact techniques for life and biosignature detection/characterization analogous to Planetary Protection Protocols. Our difficult field conditions have shared limitations common to extraterrestrial robotic and human missions. Thus, the cave/subsurface astrobiology model addresses the most important goals from both scientific and operational points of view. We present details of cave biosignature suites involving manganese and iron oxides, calcite, and sulfur minerals. Suites include morphological fossils, mineral-coated filaments, living microbial mats and preserved biofabrics, 13C and 34S values consistent with microbial metabolism, genetic data, unusual elemental abundances and ratios, and crystallographic mineral forms.