Zn biomineralization processes and microbial biofilm in a metal-rich stream (Naracauli, Sardinia)

Fungal symbionts impact cyanobacterial biofilm durability and photosynthetic efficiency

Cyanobacteria contribute to over 25% of the world's net primary photosynthetic production and are pivotal in mitigating greenhouse gas emissions.1 This study unveils a previously unobserved symbiotic relationship between benthic cyanobacteria and fungi that have also adapted to life as a plant endophyte. The interaction suggests an initial phase of lichenization. We isolated Leptolyngbya frigida from the Naracauli stream, which emanates from abandoned Zn industrial waste in Sardinia. Seasonally, L. frigida participates in a biomineralization processes, mitigating the Zn transfer to rivers and, subsequently, the sea.2,3,4L. frigida is a benthic cyanobacterium that establishes a biofilm on the stream bed. Notably, the area predominantly features Juncus acutus. From these roots, endophytic fungi were predominantly isolated as Clonostachys rosea, a fungus recognized for its biocontrol capabilities against plant pathogens. An intriguing observation was made when L. frigida was cultured with C. rosea on a low-carbohydrate agar medium: the fungal mycelium transformed into wall-less forms, a phenomenon not documented previously. In liquid environments, the resulting biofilm first settled at the container's bottom. Even upon rising to the surface, this biofilm remained pigment rich. Concurrently, a secondary biofilm began its formation at the bottom. These fungal-integrated biofilms displayed enhanced resilience and superior photosynthetic performance compared to those without fungal presence. Moreover, the symbiotic relationship significantly amplified O2 emission and CO2 sequestration by the biofilm.

Novel biological aqua crust enhances in situ metal(loid) bioremediation driven by phototrophic/diazotrophic biofilm

BACKGROUND

Understanding the ecological and environmental functions of phototrophic biofilms in the biological crust is crucial for improving metal(loid) (e.g. Cd, As) bioremediation in mining ecosystems. In this study, in combination with metal(loid) monitoring and metagenomic analysis, we systematically evaluated the effect of biofilm in a novel biological aqua crust (biogenic aqua crust-BAC) on in situ metal(loid) bioremediation of a representative Pb/Zn tailing pond.

RESULTS

We observed strong accumulation of potentially bioavailable metal(loid)s and visible phototrophic biofilms in the BAC. Furthermore, dominating taxa Leptolyngbyaceae (10.2-10.4%, Cyanobacteria) and Cytophagales (12.3-22.1%, Bacteroidota) were enriched in biofilm. Along with predominant heterotrophs (e.g. Cytophagales sp.) as well as diazotrophs (e.g. Hyphomonadaceae sp.), autotrophs/diazotrophs (e.g. Leptolyngbyaceae sp.) in phototrophic biofilm enriched the genes encoding extracellular peptidase (e.g. family S9, S1), CAZymes (e.g. CBM50, GT2) and biofilm formation (e.g. OmpR, CRP and LuxS), thus enhancing the capacity of nutrient accumulation and metal(loid) bioremediation in BAC system.

CONCLUSIONS

Our study demonstrated that a phototrophic/diazotrophic biofilm constitutes the structured communities containing specific autotrophs (e.g. Leptolyngbyaceae sp.) and heterotrophs (e.g. Cytophagales sp.), which effectively control metal(loid) and nutrient input using solar energy in aquatic environments. Elucidation of the mechanisms of biofilm formation coupled with metal(loid) immobilization in BAC expands the fundamental understanding of the geochemical fate of metal(loid)s, which may be harnessed to enhance in situ metal(loid) bioremediation in the aquatic ecosystem of the mining area. Video Abstract.

Forced Biomineralization: A Review

Biologically induced and controlled mineralization of metals promotes the development of protective structures to shield cells from thermal, chemical, and ultraviolet stresses. Metal biomineralization is widely considered to have been relevant for the survival of life in the environmental conditions of ancient terrestrial oceans. Similar behavior is seen among extremophilic biomineralizers today, which have evolved to inhabit a variety of industrial aqueous environments with elevated metal concentrations. As an example of extreme biomineralization, we introduce the category of "forced biomineralization", which we use to refer to the biologically mediated sequestration of dissolved metals and metalloids into minerals. We discuss forced mineralization as it is known to be carried out by a variety of organisms, including polyextremophiles in a range of psychrophilic, thermophilic, anaerobic, alkaliphilic, acidophilic, and halophilic conditions, as well as in environments with very high or toxic metal ion concentrations. While much additional work lies ahead to characterize the various pathways by which these biominerals form, forced biomineralization has been shown to provide insights for the progression of extreme biomimetics, allowing for promising new forays into creating the next generation of composites using organic-templating approaches under biologically extreme laboratory conditions relevant to a wide range of industrial conditions.

Chemical data on environmental matrices from an abandoned mining site

This article contains analytical data on chemical composition of waters and solid samples (mining wastes and biominerals) collected in an abandoned mining area, and they are related with the research article "Geochemistry of rare earth elements in water and solid materials at abandoned mines in SW Sardinia (Italy)" (Medas et al., 2013). Specifically, we present physicochemical data (temperature, electrical conductivity, pH, and redox potential), major components and the main contaminants (Zn, Mn, Cd, Ni, Cu, Pb) detected in stream waters and drainages from mine wastes. Waters were monitored from 2009 to 2011 during different seasonal conditions to give an insight into metal dispersion under different hydrological conditions.

Fate and effects of triclosan in subtropical river biofilms

Triclosan (TCS, 5-chloro-2-(2,4-dichlorophenoxy) phenol) is a broad-spectrum antimicrobial compound. Owing to its wide use, TCS has been frequently detected in river systems, especially in the (sub-)tropics. However, little information on its interaction with river biofilm in the (sub)tropics is currently available. In the present study, subtropical river biofilms were chronically exposed to TCS for 14 d at concentrations of 0.1-100 μg/L in artificial river water, which was followed by a 7 d recovery period. The results show that 100 μg/L TCS inhibited the growth of river biofilms and the no-observed-effect concentration (NOEC) of TCS on river biofilms was 10 μg/L. The affected biofilms did not completely recover within the 7 d of recovery period due to the adsorbed TCS which was not removed together with dissolved TCS. Exposure to TCS caused significant changes in prokaryotic species composition of river biofilms but no significant effects on eukaryotic species composition. In particular, the relative abundance of several TCS-tolerant bacterial species (e.g., Pseudoxanthomonas mexicana, Sphingopyxis alaskensis and Sphingomonas wittichii) in river biofilms increased following exposure to 10 and 100 μg/L TCS. River biofilm efficiently removed TCS from the liquid phase and the pH values of the aquatic system significantly affected the removal efficiency of TCS (from 36% at pH 6.5 to 60% at pH 8.5). No degradation products were detected in the liquid phase after 5 days of exposure, possibly due to strong adsorption of the hydrophobic degradation products to river biofilms and through biodegradation by bacteria utilizing TCS and its degradation products as source of carbon and energy for growth, such as Methyloversalitis universalis and Methylobacterium aquaticum.

Data on rare earth elements in mining environments under non-acidic conditions

This article contains analytical data on Rare Earth Elements (REE) concentration in waters and solid samples (mining wastes and biominerals) collected in an abandoned mining site characterized by near-neutral conditions, and they are related with the research article “Geochemistry of rare earth elements in water and solid materials at abandoned mines in SW Sardinia (Italy)” (Medas et al., 2013).

REE can show specific signatures due to fractionation processes, giving an insight to the understanding of the natural processes ruling the water–rock interactions and the geo–bio-interactions. Most researches on REE behavior were performed in acidic environments, while only few data on REE are available for neutral waters. Elaboration of this dataset can be useful to evaluate the reactions controlling the geochemical behavior of REE under near-neutral to slightly alkaline conditions, driving the scientific community toward an efficient management of monitoring actions and remediation technologies.

Zinc incorporation in marine bivalve shells grown in mine-polluted seabed sediments: a case study in the Malfidano mining area (SW Sardinia, Italy)

Zinc incorporation into marine bivalve shells belonging to different genera (Donax, Glycymeris, Lentidium, and Chamelea) grown in mine-polluted seabed sediments (Zn up to 1% w/w) was investigated using x-ray diffraction (XRD), chemical analysis, soft x-ray microscopy combined with low-energy x-ray fluorescence (XRF) mapping, x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). These bivalves grew their shells, producing aragonite as the main biomineral and they were able to incorporate up to 2.0-80 mg/kg of Zn, 5.4-60 mg/kg of Fe and 0.5-4.5 mg/kg of Mn. X-ray absorption near edge structure (XANES) analysis revealed that for all the investigated genera, Zn occurred as independent Zn mineral phases, i.e., it was not incorporated or adsorbed into the aragonitic lattice. Overall, our results indicated that Zn coordination environment depends on the amount of incorporated Zn. Zn phosphate was the most abundant species in Donax and Lentidium genera, whereas, Chamelea shells, characterized by the highest Zn concentrations, showed the prevalence of Zn-cysteine species (up to 56% of total speciation). Other Zn coordination species found in the investigated samples were Zn hydrate carbonate (hydrozincite) and Zn phosphate. On the basis of the coordination environments, it was deduced that bivalves have developed different biogeochemical mechanisms to regulate Zn content and its chemical speciation and that cysteine plays an important role as an active part of detoxification mechanism. This work represents a step forward for understanding bivalve biomineralization and its significance for environmental monitoring and paleoreconstruction.

Metal Tolerance Capability of Helichrysum microphyllum Cambess. subsp. tyrrhenicum Bacch., Brullo & Giusso: A Candidate for Phytostabilization in Abandoned Mine Sites

Sardinia was known as an important mine pole in Europe during his history. Still after decades from mine closure, 75.000.000 m³ of mine waste, rich in heavy metals, were left abandoned causing a huge environmental legacy on the mine district area. Consequently, cost effective remediation is required. In this frame, phytoremediation is considered a feasible candidate. This research was focused on Helichrysum microphyllum subsp. tyrrhenicum, which is pioneer in xeric soils with low-functions, like mine tailings. The aim of this study was to evaluate its ability to extract heavy metals from mine soils and accumulate them in plant tissues and its suitability for phytostabilization. Sundry samples of soil, roots and epigean organ were collected through field sampling and analysed in order to obtain metals concentration and mineralogical characteristics. Our results indicate that this species tolerates high concentration of zinc, lead and cadmium, behaving as a species suitable for phytostabilization.

Sediment heavy metals and benthic diversities in Hun-Tai River, northeast of China

In aquatic ecosystems, metal contamination in sediments has become a ubiquitous environmental problem, causing serious issues. Hun-Tai River, located in northeast of China, flows through an important heavy industry region and metropolitan area. This study examined the heavy metals (Cd, Cr, Cu, Fe, Mn, Pb, Ni, and Zn) of sediments and diversities (taxa richness, Shannon diversity, and evenness) of benthic assemblages (benthic algae and macroinvertebrate) in Hun-Tai River. The results clearly described the spatial patterns of metal contamination in terms of geo-accumulation index and contamination factor, as well as the spatial patterns of benthic diversities in terms of taxa richness, Shannon index, and evenness by kriging interpolation. The sediments were largely contaminated by Cd, followed by Cu, Fe, Zn, Mn, and Ni. Cd and Zn had similar spatial patterns and similar sources. Cu, Fe, Mn, and Ni showed similar spatial patterns and similar sources. The surface sediments were unpolluted by Cr and Pb. The metal mines and the heavy industry in the major cities were the potential pollution sources. Benthic algae and macroinvertebrate responded similarly to the heterogeneous environment and metal contamination, with high taxa richness and Shannon index in middle-upper reaches of Hun-Tai River. Evenness showed complex spatial patterns. Under low contamination, both taxa richness, Shannon diversity, and evenness had a large variation range. However, under the moderate and high contamination, the taxa richness and Shannon diversity kept to a low level but the evenness had a high level. This study provided insights into the sediment heavy metal contamination in Hun-Tai River.

Scrutinizing the influence of UV radiation on adsorption behavior of zinc metal on marine diatom Nitzschia sp. BDU DD 002

The present study is an investigation into the adsorption of zinc metal on marine diatom Nitzschia sp. under the influence of ultraviolet radiation to reveal the possible role of radiation in metal biomineralization. Nitzschia sp. was isolated from marine habitat and gradually acclimatized to UVA, UVB, and zinc (30 mg/L). The culture was subjected to various concentrations of zinc (5, 10, 15, 20 mg/L) with an artificial exposure of PAR, PAR + UVA, and PAR + UVB radiation. The adsorption isotherm models were applied for validating the hypothesis stating the association of zinc adsorption with exposure to ultraviolet radiation. Altered functional groups on the surface were observed in the FTIR spectra along with changes in antioxidant activity, superoxide dismutase activity, pigment and protein contents due to increased zinc concentration and ultraviolet radiation. Scanning electron micrographs (SEM-EDAX) supported the microscopic morphology of adsorbed metals.

Metals and metalloids in hair samples of children living near the abandoned mine sites of Sulcis-Inglesiente (Sardinia, Italy)

The Sulcis-Iglesiente district (SW Sardinia, Italy) is one of the oldest and most important polymetallic mining areas in Italy. Large outcrops of sulfide and oxide ores, as well as the products of the long-lasting mining activity, are present throughout the district releasing significant quantities of metals and metalloids into the surrounding environment. Here are reported concentrations of 21 elements determined in scalp hair samples from children (aged 11-13 years) living in different geochemical environments of southwestern Sardinia: Iglesias, hosting several abandoned mines, and the island of Sant׳Antioco, not affected by significant base metal mineralization events. Trace element determinations were performed by ICP-MS. Statistically significant differences (p<0.01) in elemental concentration levels between the two study sites were found. Hair of children from Iglesias exhibited higher concentration values for Ag, Ba, Cd, Cr, Ni, Pb, Rb, Sb, U, V, and Zn. Rubidium, V and U resulted more abundant at Sant׳Antioco. Hair samples from Iglesias showed gender-related differences for a larger number of elements (Ag, Ba, Cd, Co, Cu, Ni, Sr, U and Zn) than at Sant׳Antioco, where only U was significantly different. The above elemental concentrations in females were always higher than in male donors. Robust Principal Component Analysis operated on log-transformed elemental concentrations showed components indicative of a) sulfides ore minerals (PC1) reflecting the influence of the diffuse mineralization covering the entire study area, b) the presence of some bioavailable As sources (PC2) as As-rich pyrite and Fe-containing sphalerite and c) other sources of metals overlapping the diffuse mineralizations, as carbonate rocks and coal deposits (PC3). The results provided evidence of a potential risk of adverse effects on the health of the exposed population, with children living at Iglesias being greatly exposed to several metals and metalloids originated in mining tailings, enriched soils, waters and food.

The amorphous Zn biomineralization at Naracauli stream, Sardinia: electron microscopy and X-ray absorption spectroscopy

An amorphous Zn biomineralization ("white mud"), occurring at Naracauli stream, Sardinia, in association with cyanobacteria Leptolyngbya frigida and diatoms, was investigated by electron microscopy and X-ray absorption spectroscopy. Preliminary diffraction analysis shows that the precipitate sampled on Naracauli stream bed is mainly amorphous, with some peaks ascribable to quartz and phyllosilicates, plus few minor unattributed peaks. Scanning electron microscopy analysis shows that the white mud, precipitated in association with a seasonal biofilm, is made of sheaths rich in Zn, Si, and O, plus filaments likely made of organic matter. Transmission electron microscopy analysis shows that the sheaths are made of smaller units having a size in the range between 100 and 200 nm. X-ray absorption near-edge structure and extended X-ray absorption fine structure data collected at the Zn K-edge indicate that the biomineral has a local structure similar to hemimorphite, a zinc sorosilicate. The differences of this biomineral with respect to the hydrozincite biomineralization documented about 3 km upstream in the same Naracauli stream may be related to either variations in the physicochemical parameters and/or different metabolic behavior of the involved biota.