Microbially Mediated Calcium Carbonate Precipitation: Implications for Interpreting Calcite Precipitation and for Solid-Phase Capture of Inorganic Contaminants

Microbial degradation of urea was investigated as a potential geochemical catalyst for Ca carbonate precipitation and associated solid phase capture of common groundwater contaminants (Sr, UO₂, Cu) in laboratory batch experiments. Bacterial degradation of urea increased pH and promoted Ca carbonate precipitation in both bacterial control and contaminant treatments. Associated solid phase capture of Sr was highly effective, capturing 95% of the 1 mM Sr added within 24 h. The results for Sr are consistent with solid solution formation rather than discrete Sr carbonate phase precipitation. In contrast, UO₂ capture was not as effective, reaching only 30% of the initial 1 mM UO₂ added, and also reversible, dropping to 7% by 24 h. These results likely reflect differing sites of incorporation of these two elements-Ca lattice sites for Sr versus crystal defect sites for UO₂. Cu sequestration was poor, resulting from toxicity of the metal to the bacteria, which arrested urea degradation and concomitant Ca carbonate precipitation. Scanning electron microscopy (SEM) indicated a variety of morphologies reminiscent of those observed in the marine stromatolite literature. In bacterial control treatments, X-ray diffraction (XRD) analyses indicated only calcite; while in the presence of either Sr or UO₂, both calcite and vaterite, a metastable polymorph of Ca carbonate, were identified. Tapping mode atomic force microscopy (AFM) indicated differences in surface microtopography among abiotic, bacterial control, and bacterial contaminant systems. These results indicate that Ca carbonate precipitation induced by passive biomineralization processes is highly effective and may provide a useful bioremediation strategy for Ca carbonate-rich aquifers where Sr contamination issues exist.     

Trophic structure of macrobenthos in the Tagus estuary and adjacent coastal shelf

The trophic structure of benthic communities in the Tagus estuary and adjacent coastal shelf was characterized according to a functional guild approach, based on sampling surveys conducted between 1987 and 2000. Macrobenthic organisms were assigned to seven distinct trophic groups (herbivorous, filter feeders, surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders/detritivores, carnivores/detritivores) and the dominance of these groups was related to environmental variables using multivariate ordination techniques. Surface-deposit feeders were numerically dominant in the Tagus estuary, making up 52% of the benthic communities, while in the adjacent coastal shelf the assemblage was dominated by both surface-deposit feeders and filter feeders (37% and 33%, respectively). When biomass was considered, filter feeders and filter feeders/detritivores were the dominant groups in the estuary, while for the adjacent coastal shelf filter feeders represented 83% of the total biomass. Salinity, depth and sediment composition were the main factors structuring spatial distribution. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary. Surface deposit feeders also dominated the middle and the lower estuary but the proportion of filter feeders as well as other trophic groups increased with salinity. Generally, a more even distribution of trophic structure was found at stations with high salinity. In the adjacent coastal shelf, the trophic diversity decreased with depth. The trophic structure revealed that filter feeders dominated in abundance and biomass in shallow sandy sediments (<25 m), while in deeper sandy mud and muddy habitats (>50 m to 260 m), deposit feeders and carnivores were the most important groups in abundance and biomass, respectively.     

Lipid and fatty acid biomarkers as proxies for environmental contamination in caged mussels Mytilus galloprovincialis

Mussels (Mytilus galloprovincialis) were transplanted from a reference site (Syracuse harbour) to an impacted site (Augusta Bay) from January to July 2013 to assess the biochemical response of caged mussels to high trace element and polycyclic aromatic hydrocarbon (PAH) contamination, using lipid and fatty acid (FA) biomarkers. Sediment and mussels were analysed to assess contaminant bioavailability in the study sites and bioaccumulation in mussel tissue. Trace elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, Zn) and PAHs were significantly higher in mussels from Augusta than in those from Syracuse, mirroring the different environmental contamination. The biological impact quotient (BIQs), which indicates the potential biological impact of mussel-accumulated contaminants, reflected the highest contaminant concentrations found in Augusta and their temporal trend, which increased from the start of the experiment to 3–4 months after transplanting, followed by a decrease, as indication of mussel detoxification processes. Lower condition index (CI) and phospholipids (PL), as well as higher total (TL) and neutral lipids (NL) in mussels from Augusta, indicated the occurrence of a physiological and biochemical stress response to pollutant exposure and accumulation. Differences in FA composition, especially polyunsaturated (PUFA), essential (EFA) and non-methylene interrupted dienoic (NMID) FAs between the study sites revealed the occurrence of stress-induced lipid peroxidation, followed by compensatory/adaptive processes in Augusta mussels. The marked increase in bacterial biomarkers, mainly cyclopropyl (CY) FAs, reflecting the greater bioaccumulation of chemicals in the Augusta mussels, may be the result of bacterial infections or symbiosis with bacteria involved in detoxification processes.     

DNA damage as a bivalve biomarker

Bivalves have been used in numerous environmental assessment studies, chiefly because they are sessile deposit or suspension feeding organisms found in or near sites of environmental concern, and they can be easily collected, sorted and deployed at sites of interest. Monitoring studies utilizing bivalves currently rely on the comparison of growth, survival, and contaminant bioaccumulation. Data gathered from 'reference' sites are compared with those of populations at assessment sites. These studies require extended periods of exposure, lasting weeks to months, and the use of a well defined population of test organisms of similar size, age, and condition. In many cases time and resources require researchers to restrict their sampling to the organisms on-hand at a particular site without the benefit of any reference data. Therefore more versatile and sensitive assessment methods are needed. Because effects at higher levels of organization such as growth, development, and survival are initiated at the molecular and cellular levels attempts have been made to identify useful biomarkers at these levels. The proposed advantages of molecular/cellular biomarkers are that they will respond to stress predictably and more rapidly, and will be indicative of the mechanisms of toxicity thereby yielding a rudimentary characterization of the contaminant(s) influencing them. In the following communication we will report on past and current developments in the monitoring of DNAdamage as an environmental biomarker.     

Application of redox mediators in bioelectrochemical systems

Redox mediators (RM) are natural or artificial compounds used by microorganisms as electron acceptors and electron donors during electron transfer. Evidence collected in the last years indicates that the application of RM in bioelectrochemical systems (BES) enhanced the electron transfer from microorganisms to anodes and from cathodes to microorganisms. This review summarizes the results of using soluble or immobilized RM in BES to produce electricity and for the treatment of contaminants from wastewater effluents. In addition, future research focused on biohydrogen production, recovery or removal metals, and the use of humic substances (HS) extracted from natural environment is proposed.     

Appropriate experimental design for transplanting mussels (Mytilus sp.) in analyses of environmental stress: an example in Sydney Harbour (Australia)

Some locations in Sydney Harbour (Sydney, Australia) contain large amounts of contaminants (heavy metals and hydrocarbons), sometimes in concentrations thought to affect biological systems. In order to estimate effects of sediment-bound contaminants on the physiology of organisms living above the sediment, the rates of clearance and respiration and the efficiency of absorption of mussels, Mytilus sp., living in a contaminated location were measured, the scope for growth (SfG) was calculated and compared to that of mussels living in uncontaminated locations. Two different models were proposed to explain expected differences. The first was that the contaminants at the impacted location reduced the SfG of local mussels; the second was that at the contaminated location only those mussels survived that had a small SfG (genetic differences between populations might be a reason for differential survival). To test which model applied, mussels were transplanted between the contaminated and uncontaminated locations. Moving and disturbing mussels (handling, tagging and caging) required the inclusion of two control treatments. These treatments were essential for a proper evaluation of the results but have generally not been included in similar studies. Effects of moving were estimated by translocating mussels from the uncontaminated and from the contaminated location to similar locations. To estimate effects of disturbance, mussels in the experimental locations were given the same treatment as the experimental mussels, but were returned to the place of origin. It was predicted that translocating and disturbing mussels would have no effect on the SfG, which would be similar to that of mussels at the place of origin. As expected, SfG was smaller (because rate of clearance was reduced) in undisturbed mussels at the contaminated location compared with those of mussels at the uncontaminated location. Because there were significant effects of disturbance on the SfG of mussels at the contaminated location, it was concluded that this difference was not caused by differences between the amounts of contaminants in the two locations, but was caused by other confounding factors (physical disturbance by crabs and fouling organisms). That the interpretation of the results would have been different if proper controls were not included is discussed in this paper and the importance of proper experimental controls is stressed.     

Resistance to oxidative damage but not immunosuppression by organic tin compounds in natural populations of Daubenton's bats (Myotis daubentonii)

The acute toxicity of organic tin compounds (OTCs) has been studied in detail. However, due to their complex nature, very little is known about species-specific methods of accumulation and consequences for food-webs. Chironomids, on which e.g. Daubenton's bats feed, may act as vectors for the transport of organic tin compounds from aquatic to terrestrial ecosystems. Bats are prone to environmental toxins because of their longevity and their ecological role as top predators. Organic tin compounds are associated with increased formation of reactive oxygen species and associated oxidative damage as well as suppression of immune function. The present paper investigates whether the OTC, tributyltin (TBT) and its metabolite, dibutyltin (DBT), accumulate in natural populations of Daubenton's bats and whether TBT-associated effects are seen in general body condition, redox balance, redox enzyme activities, associated oxidative damage of red blood cells and complement function. We discovered the concentration of bat fur DBT correlated with local marine sediment TBT concentrations. However, we did not find a correlation between the explanatory factors, bat fur DBT and marine sediment TBT concentrations, and several physiological and physical response variables apart from complement activity. Higher DBT concentrations resulted in weaker complement activity and thus a weaker immune response. Although the observed physiological effects in the present study were not strongly correlated to butyltin concentrations in fur or sediment, the result is unique for natural populations so far and raises interesting questions for future ecotoxicological studies.     

Method for suppressing non-specific protein interactions observed with affinity resins

Previous high throughput data analysis from several different approaches to affinity purification of protein complexes have revealed catalogues of contaminating proteins that persistently co-purify. Some of these contaminating proteins appear to be specific to one particular affinity matrix used or even to the artificial affinity tags introduced into endogenous proteins for the purpose of purification.A recent approach to minimising non-specific protein interactions in high throughput screens utilises pre-equilibration of affinity surfaces with thiocyanate anions to reduce non-specific binding of proteins. This approach not only reduces the effect of contaminating proteins but also promotes the enrichment of the specific binding partners. Here, we have taken this method and adapted it in an attempt to reduce the abundance of common contaminants in affinity purification experiments. We found the effect varied depending on the bait used, most likely due to its endogenous abundance.     

Assessing nutrient salts and trace metals distributions in the coastal water of Jeddah,Red Sea

In this study, eighteen sites at Jeddah coastal area, Red Sea, have been assessed for water quality status, depending on nutrients, metals, Chlorophyll-a (Chl-a) and physical variables during 2018 and 2019. The investigated parameters of the Water Quality Index (WQI) are temperature, pH, salinity, dissolved oxygen (DO), DO saturation, oxidizable organic matter (OOM), suspended particulate matter (SPM), Chl-a, ammonium, nitrite, nitrate, total nitrogen, reactive phosphate, total phosphorus, silicate, Zn, Fe, Mn Cu, Cd, Pb, and Ni. The results revealed that the pH values were slightly alkaline with a range of 7.85–8.20. The results of other parameters were as follow: salinity (36.95–42.61PSU), DO (5.22–6.67 mg/L), OOM (0.40–1.23 mg/L), SPM (12.39–21.5 mg/L), Chl-a (0.10–0.83 µg/L). The range of nutrients (μM) were 0.07–0.22, 0.45–1.47, 9.62–18.64, 23.31–57.65, 0.05–0.15, 0.55–2.78 and 2.54–5.51 for NH₄/N, NO₂/N, NO₃/N, TN, PO₄/P, TP and SiO₄/Si, respectively. Cluster analysis was used to classify the stations studied. From the current study, five clusters were found, indicating the need to perform cluster analysis in the water quality assessment process to confirm the durability and consistency of the data discovered in the current application.     

Cyanobacteria as a source of biofertilizers for sustainable agriculture

Continuous increase in global human population and depletion of natural resources of energy posing threat to environment needs, sustainable supply of food and energy. The most ecofriendly approach ‘green technology’ has been exploited for biofertilizer preparation. Cyanobacteria are the most successful and sustained prokaryotic organism during the course of evolution. They are considered as one of the primitive life forms found on our planet. Cyanobacteria are emerging candidates for efficiently conversion of radiant energy into chemical energy. This biological system produces oxygen as a by-product. Cyanobacterial biomass can also be used for the large scale production of food, energy, biofertilizers, secondary metabolites, cosmetics and medicines. Therefore, cyanobacteria are used in ecofriendly sustainable agricultural practice for production of biomass of very high value and decreasing the level of CO_2. This review article describes the methods of mass production of cyanobacterial biofertilizers and their applications in agriculture and industrial level.