Insights Into the Mineralogy and Surface Chemistry of Extracellular Biogenic S0 Globules Produced by Chlorobaculum tepidum

Quantitative proteomics reveals the Sox system's role in sulphur and arsenic metabolism of phototroph Halorhodospira halophila

The metabolic process of purple sulphur bacteria's anoxygenic photosynthesis has been primarily studied in Allochromatium vinosum, a member of the Chromatiaceae family. However, the metabolic processes of purple sulphur bacteria from the Ectothiorhodospiraceae and Halorhodospiraceae families remain unexplored. We have analysed the proteome of Halorhodospira halophila, a member of the Halorhodospiraceae family, which was cultivated with various sulphur compounds. This analysis allowed us to reconstruct the first comprehensive sulphur-oxidative photosynthetic network for this family. Some members of the Ectothiorhodospiraceae family have been shown to use arsenite as a photosynthetic electron donor. Therefore, we analysed the proteome response of Halorhodospira halophila when grown under arsenite and sulphide conditions. Our analyses using ion chromatography-inductively coupled plasma mass spectrometry showed that thioarsenates are chemically formed under these conditions. However, they are more extensively generated and converted in the presence of bacteria, suggesting a biological process. Our quantitative proteomics revealed that the SoxAXYZB system, typically dedicated to thiosulphate oxidation, is overproduced under these growth conditions. Additionally, two electron carriers, cytochrome c551/c5 and HiPIP III, are also overproduced. Electron paramagnetic resonance spectroscopy suggested that these transporters participate in the reduction of the photosynthetic Reaction Centre. These results support the idea of a chemically and biologically formed thioarsenate being oxidized by the Sox system, with cytochrome c551/c5 and HiPIP III directing electrons towards the Reaction Centre.

Optimizing Autotrophic Sulfide Oxidation in the Oxygen-Based Membrane Biofilm Reactor to Recover Elemental Sulfur

Biological sulfide oxidation is an efficient means to recover elemental sulfur (S0) as a valuable resource from sulfide-bearing wastewater. This work evaluated the autotrophic sulfide oxidation to S0 in the O2-based membrane biofilm reactor (O2-MBfR). High recovery of S0 (80-90% of influent S) and high sulfide oxidation (∼100%) were simultaneously achieved when the ratio of O2-delivery capacity to sulfide-to S0 surface loading (SL) (O2/S2- → S0 ratio) was around 1.5 (g O2/m2-day/g O2/m2-day). On average, most of the produced S0 was recovered in the MBfR effluent, although the biofilm could be a source or sink for S0. Shallow metagenomic analysis of the biofilm showed that the top sulfide-oxidizing genera present in all stages were Thauera, Thiomonas, Thauera_A, and Pseudomonas. Thiomonas or Pseudomonas was the most important genus in stages that produced almost only S0 (i.e., the O2/S2- → S0 ratio around 1.5 g of the O2/m2-day/g O2/m2-day). With a lower sulfide SL, the S0-producing genes were sqr and fccAB in Thiomonas. With a higher sulfide SL, the S0-producing genes were in the soxABDXYZ system in Pseudomonas. Thus, the biofilm community of the O2-MBfR adapted to different sulfide-to-S0 SLs and corresponding O2-delivery capacities. The results illustrate the potential for S0 recovery using the O2-MBfR.

Physiological and Genomic Characterization of a Novel Obligately Chemolithoautotrophic, Sulfur-Oxidizing Bacterium of Genus Thiomicrorhabdus Isolated from a Coastal Sediment

Thiomicrorhabdus species, belonging to the family Piscirickettsiaceae in the phylum Pseudomonadotav are usually detected in various sulfur-rich marine environments. However, only a few bacteria of Thiomicrorhabdus have been isolated, and their ecological roles and environmental adaptations still require further understanding. Here, we report a novel strain, XGS-01T, isolated from a coastal sediment, which belongs to genus Thiomicrorhabdus and is most closely related to Thiomicrorhabdus hydrogeniphila MAS2T, with a sequence similarity of 97.8%. Phenotypic characterization showed that XGS-01T is a mesophilic, sulfur-oxidizing, obligate chemolithoautotrophy, with carbon dioxide as its sole carbon source and oxygen as its sole electron acceptor. During thiosulfate oxidation, strain XGS-01T can produce extracellular sulfur of elemental α-S8, as confirmed via scanning electron microscopy and Raman spectromicroscopy. Polyphasic taxonomy results indicate that strain XGS-01T represents a novel species of the genus Thiomicrorhabdus, named Thiomicrorhabdus lithotrophica sp. nov. Genomic analysis confirmed that XGS-01T performed thiosulfate oxidation through a sox multienzyme complex, and harbored fcc and sqr genes for sulfide oxidation. Comparative genomics analysis among five available genomes from Thiomicrorhabdus species revealed that carbon fixation via the oxidation of reduced-sulfur compounds coupled with oxygen reduction is conserved metabolic pathways among members of genus Thiomicrorhabdus.

Fluorescence Microscopy Study of the Intracellular Sulfur Globule Protein SgpD in the Purple Sulfur Bacterium Allochromatium vinosum

When oxidizing reduced sulfur compounds, the phototrophic sulfur bacterium Allochromatium vinosum forms spectacular sulfur globules as obligatory intracellular-but extracytoplasmic-intermediates. The globule envelope consists of three extremely hydrophobic proteins: SgpA and SgpB, which are very similar and can functionally replace each other, and SgpC which is involved in the expansion of the sulfur globules. The presence of a fourth protein, SgpD, was suggested by comparative transcriptomics and proteomics of purified sulfur globules. Here, we investigated the in vivo function of SgpD by coupling its carboxy-terminus to mCherry. This fluorescent protein requires oxygen for chromophore maturation, but we were able to use it in anaerobically growing A. vinosum provided the cells were exposed to oxygen for one hour prior to imaging. While mCherry lacking a signal peptide resulted in low fluorescence evenly distributed throughout the cell, fusion with SgpD carrying its original Sec-dependent signal peptide targeted mCherry to the periplasm and co-localized it exactly with the highly light-refractive sulfur deposits seen in sulfide-fed A. vinosum cells. Insertional inactivation of the sgpD gene showed that the protein is not essential for the formation and degradation of sulfur globules.

Insights into the sulfur metabolism of Chlorobaculum tepidum by label-free quantitative proteomics

Chlorobaculum tepidum is an anaerobic green sulfur bacterium which oxidizes sulfide, elemental sulfur, and thiosulfate for photosynthetic growth. It can also oxidize sulfide to produce extracellular S0 globules, which can be further oxidized to sulfate and used as an electron donor. Here, we performed label-free quantitative proteomics on total cell lysates prepared from different metabolic states, including a sulfur production state (10 h post-incubation [PI]), the beginning of sulfur consumption (20 h PI), and the end of sulfur consumption (40 h PI), respectively. We observed an increased abundance of the sulfide:quinone oxidoreductase (Sqr) proteins in 10 h PI indicating a sulfur production state. The periplasmic thiosulfate-oxidizing Sox enzymes and the dissimilatory sulfite reductase (Dsr) subunits showed an increased abundance in 20 h PI, corresponding to the sulfur-consuming state. In addition, we found that the abundance of the heterodisulfide-reductase and the sulfhydrogenase operons was influenced by electron donor availability and may be associated with sulfur metabolism. Further, we isolated and analyzed the extracellular sulfur globules in the different metabolic states to study their morphology and the sulfur cluster composition, yielding 58 previously uncharacterized proteins in purified globules. Our results show that C. tepidum regulates the cellular levels of enzymes involved in sulfur metabolism in response to the availability of reduced sulfur compounds.

Organic layer characteristics and microbial utilization of the biosulfur globules produced by haloalkaliphilic Thioalkalivibrio versutus D301 during biological desulfurization

The haloalkaliphilic genus Thioalkalivibrio, widely used in bio-desulfurization, can oxidize H₂S to S^o, which is excreted outside cells in the form of biosulfur globules. As by-product of bio-desulfurization, information on biosulfur globules is still very scant, which limits its high-value utilization. In this paper, the characteristics of biosulfur globules produced by Thioalkalivibrio versutus D301 and the possibility of cultivating sulfur-oxidizing bacteria as a high biological-activity sulfur source were studied. The sulfur element in the biosulfur globules existed in the form α-S₈, which was similar to chemical sulfur. The biosulfur globule was wrapped with an organic layer composed of polysaccharides and proteins. The composition of this organic layer could change. In the formation stage of biosulfur globules, the organic layer was dominated by polysaccharides, and in later stage, proteins became the main component. We speculated that the organic layer was mainly formed by the passive adsorption of organic matter secreted by cells. The existence of organic layer endowed biosulfur with better bioavailability. Compared with those found using chemical sulfur, the growth rates of Acidithiobacillus thiooxidans ATCC 19377^T, Thiomicrospira microaerophila BDL05 and Thioalkalibacter halophilus BDH06 using biosulfur increased several folds to an order of magnitude, indicating that biosulfur was a good sulfur source for cultivating sulfur-oxidizing bacteria.

Deep-Sea In Situ Insights into the Formation of Zero-Valent Sulfur Driven by a Bacterial Thiosulfate Oxidation Pathway

The contribution of microbes to the deep-sea cold seep sulfur cycle has received considerable attention in recent years. In the previous study, we isolated E. flavus 21-3 from deep-sea cold seep sediments and described a novel thiosulfate oxidation pathway in the laboratorial condition.

In situ bio/chemical characterization of Venus cloud particles using Life-signature Detection Microscope for Venus (Venus LDM)

Much of the information about the size and shape of aerosols forming haze and the cloud layer of Venus is obtained from indirect inferences from nephelometers on probes and from analysis of the variation of polarization with the phase angle and the glory feature from images of Venus. Microscopic imaging of Venus' aerosols has been advocated recently. Direct measurements from a fluorescence microscope can provide information on the morphology, density, and biochemical characteristics of the particles; thus, the fluorescence microscope is attractive for the in situ particle characterization of Venus' cloud layer. Fluorescence imaging of Venus' cloud particles presents several challenges due to the sulfuric acid composition and the corrosive effects. In this article, we identify the challenges and describe our approach to overcoming them for a fluorescence microscope based on an in situ bio/chemical and physical characterization instrument for use in the clouds of Venus from a suitable aerial platform. We report that a pH adjustment using alkali was effective for obtaining fluorescence images, and that fluorescence attenuation was observed after the adjustment, even when the acidophile suspension in the concentrated sulfuric acid was used as a sample.

The pathway of sulfide oxidation to octasulfur globules in the cytoplasm of aerobic bacteria

Sulfur-oxidizing bacteria can oxidize hydrogen sulfide (H₂S) to produce sulfur globules. Although the process is common, the pathway is unclear. In recombinant Escherichia coli and wild-type Corynebacterium vitaeruminis DSM20294 with SQR but no enzymes to oxidize zero valence sulfur, SQR oxidized H₂S into short-chain inorganic polysulfide (H₂S_n, n≥2) and organic polysulfide (RS_nH, n≥2), which reacted with each other to form long-chain GS_nH (n≥2) and H₂S_n before producing octasulfur (S₈), the main component of elemental sulfur. GS_nH also reacted with GSH to form GSnG (n≥2) and H₂S; H₂S was again oxidized by SQR. After GSH was depleted, SQR simply oxidized H₂S to H₂S_n, which spontaneously generated S₈. S₈ aggregated into sulfur globules in the cytoplasm. The results highlight the process of sulfide oxidation to S₈ globules in the bacterial cytoplasm and demonstrate the potential of using heterotrophic bacteria with SQR to convert toxic H₂S into relatively benign S₈ globules. IMPORTANCE Our results support a process of H₂S oxidation to produce octasulfur globules via SQR catalysis and spontaneous reactions in the bacterial cytoplasm. Since the process is an important event in geochemical cycling, a better understanding facilitates further studies and provides theoretical support for using heterotrophic bacteria with SQR to oxidize toxic H₂S into sulfur globules for recovery.

Novel Agglomeration Strategy for Elemental Sulfur Produced during Biological Gas Desulfurization

This article presents a novel crystal agglomeration strategy for elemental sulfur (S) produced during biological desulfurization (BD). A key element is the nucleophilic dissolution of S by sulfide (HS-) to polysulfides (S x 2-), which was enhanced by a sulfide-rich, anoxic reactor. This study demonstrates that with enhanced S x 2- formation, crystal agglomerates are formed with a uniform size (14.7 ± 3.1 μm). In contrast, with minimal S x 2- formation, particle size fluctuates markedly (5.6 ± 5.9 μm) due to the presence of agglomerates and single crystals. Microscopic analysis showed that the uniformly sized agglomerates had an irregular structure, whereas the loose particles and agglomerates were more defined and bipyramidal. The irregular agglomerates are explained by dissolution of S by (poly)sulfides, which likely changed the crystal surface structure and disrupted crystal growth. Furthermore, S from S x 2- appeared to form at least 5× faster than from HS- based on the average S x 2- chain length of x ≈ 5, thereby stimulating particle agglomeration. In addition, microscopy suggested that S crystal growth proceeded via amorphous S globules. Our findings imply that the crystallization product is controlled by the balance between dissolution and formation of S. This new insight has a strong potential to prevent poor S settleability in BD.

Metagenomics and metatranscriptomics uncover the microbial community associated with high S0 production in a denitrifying desulfurization granular sludge reactor

The denitrification desulfurization process is a promising technology for elemental sulfur (S⁰) production from sulfide containing wastewater. However, the microbial community associated with high S⁰ production still is not well studied. This study describes an efficient denitrification S⁰ production bioreactor based on inoculation with anaerobic granular sludge. At an optimal S/N molar ratio of 7:2, 80 % of the influent sulfide was transformed to high quality elemental sulfur with a purity of 92.5% while the total inorganic nitrogen removal efficiency was stable at ∼80%. Metatranscriptomic analysis found that community expression of the gene encoding the sulfide-quinone reductase (SQR) was 10-fold greater than that of the flavocytochrome-c sulfide dehydrogenase subunit B (fccB). Moreover, the expression level of SQR was also significantly higher than the Dsr gene encoding for dissimilatory sulfate reductase, which encodes a critical S⁰ oxidation enzyme. Metagenomic binning analysis confirmed that sulfide-oxidizing bacteria (SOB) utilizing SQR were common in the community and most likely accounted for high S⁰ production. An unexpected enrichment in methanogens and high expression activity of bacteria carrying out Stickland fermentation as well as in other bacteria with reduced genomes indicated a complex community supporting stable sulfide oxidation to S⁰, likely aiding in performance stability. This study establishes this treatment approach as an alternative biotechnology for sulfide containing wastewater treatment and sheds light on the microbial interactions associated with high S⁰ production.

Organic Stabilization of Extracellular Elemental Sulfur in a Sulfurovum-Rich Biofilm: A New Role for Extracellular Polymeric Substances?

This work shines light on the role of extracellular polymeric substance (EPS) in the formation and preservation of elemental sulfur biominerals produced by sulfur-oxidizing bacteria. We characterized elemental sulfur particles produced within a Sulfurovum-rich biofilm in the Frasassi Cave System (Italy). The particles adopt spherical and bipyramidal morphologies, and display both stable (α-S8) and metastable (β-S8) crystal structures. Elemental sulfur is embedded within a dense matrix of EPS, and the particles are surrounded by organic envelopes rich in amide and carboxylic groups. Organic encapsulation and the presence of metastable crystal structures are consistent with elemental sulfur organomineralization, i.e., the formation and stabilization of elemental sulfur in the presence of organics, a mechanism that has previously been observed in laboratory studies. This research provides new evidence for the important role of microbial EPS in mineral formation in the environment. We hypothesize that the extracellular organics are used by sulfur-oxidizing bacteria for the stabilization of elemental sulfur minerals outside of the cell wall as a store of chemical energy. The stabilization of energy sources (in the form of a solid electron acceptor) in biofilms is a potential new role for microbial EPS that requires further investigation.

Characterization of Sulfurimonas hydrogeniphila sp. nov., a Novel Bacterium Predominant in Deep-Sea Hydrothermal Vents and Comparative Genomic Analyses of the Genus Sulfurimonas

Bacteria of the genus Sulfurimonas within the class Campylobacteria are predominant in global deep-sea hydrothermal environments and widespread in global oceans. However, only few bacteria of this group have been isolated, and their adaptations for these extreme environments remain poorly understood. Here, we report a novel mesophilic, hydrogen- and sulfur-oxidizing bacterium, strain NW10T, isolated from a deep-sea sulfide chimney of Northwest Indian Ocean.16S rRNA gene sequence analysis showed that strain NW10T was most closely related to the vent species Sulfurimonas paralvinellae GO25T with 95.8% similarity, but ANI and DDH values between two strains were only 19.20 and 24.70%, respectively, indicating that strain NW10 represents a novel species. Phenotypic characterization showed strain NW10T is an obligate chemolithoautotroph utilizing thiosulfate, sulfide, elemental sulfur, or molecular hydrogen as energy sources, and molecular oxygen, nitrate, or elemental sulfur as electron acceptors. Moreover, hydrogen supported a better growth than reduced sulfur compounds. During thiosulfate oxidation, the strain can produce extracellular sulfur of elemental α-S8 with an unknown mechanism. Polyphasic taxonomy results support that strain NW10T represents a novel species of the genus Sulfurimonas, and named as Sulfurimonas hydrogeniphila sp. nov. Genome analyses revealed its diverse energy metabolisms driving carbon fixation via rTCA cycling, including pathways of sulfur/hydrogen oxidation, coupled oxygen/sulfur respiration and denitrification. Comparative analysis of the 11 available genomes from Sulfurimonas species revealed that vent bacteria, compared to marine non-vent strains, possess unique genes encoding Type V Sqr, Group II, and Coo hydrogenase, and are selectively enriched in genes related to signal transduction and inorganic ion transporters. These phenotypic and genotypic features of vent Sulfurimonas may explain their thriving in hydrothermal environments and help to understand the ecological role of Sulfurimonas bacteria in hydrothermal ecosystems.

Transcriptional response of Thialkalivibrio versutus D301 to different sulfur sources and identification of the sulfur oxidation pathways

The genus Thialkalivibrio plays an essential role in the biological desulfurization system. However, to date, the sulfur oxidation pathways of Thialkalivibrio are not clearly understood. Here, we performed transcriptomic analysis on Thialkalivibrio versutus D301 with either thiosulfate or chemical sulfur as the sulfur source to understand it. The results show that T. versutus D301 has a higher growth rate and sulfur oxidation activity when thiosulfate is utilized. The use of chemical sulfur as sulfur source leads to decreased expression of genes involved in carbon metabolism, ribosome synthesis and oxidative phosphorylation in T. versutus D301. Potentially due to the adsorption to sulfur particles, the genes related to flagellum assembly and motivation are significantly induced in T. versutus D301 in the presence of chemical sulfur. In the periplasm, both thiosulfate and polysulfide from the chemical sulfur are oxidized to sulfate via the similar truncated Sox system (SoxAXYZB). Then, part of polysulfide reached to cytoplasm through an unidentified route is oxidized to sulfite by the Dsr-like system. The sulfite in the cytoplasm is further catalyzed to sulfate by SoxB or SoeABC. Overall, the difference in the oxidation rates of D301 can be mainly attributed to the bioavailability of the two sulfur sources, not the sulfur oxidation pathways.

Molecular Characterization of Extended-Spectrum β-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Among the Pediatric Population in Qatar

INTRODUCTION

Although extended-spectrum β-lactamase (ESBL)-producing Enterobacterales are a public health problem in the Arabian Peninsula, data on the molecular characteristic of their antimicrobial resistance determinants in children is limited.

AIM

To determine the molecular characteristics of ESBL-producing Escherichia coli and Klebsiella pneumoniae in the pediatric population of Qatar.

METHODS

Whole-genome sequencing was performed on ESBL-producing E. coli and K. pneumoniae isolates recovered from screening and clinical specimens from pediatric patients at Sidra Medicine in Doha from January to December 2018.

RESULTS

A total of 327 ESBL producers were sequenced: 254 E. coli and 73 K. pneumoniae. Non-susceptibility rates to non-β-lactam antibiotics for both species were 18.1 and 30.1% for gentamicin, 0.8 and 4.1% for amikacin, 41.3 and 41.1% for ciprofloxacin, and 65.8 and 76.1% for cotrimoxazole. The most common sequence types (STs) were ST131 (16.9%), ST38 and ST10 (8.2% each) in E. coli and ST307 (9.7%), and ST45 and ST268 (6.9% each) in K. pneumoniae. CTX-M type ESBLs were found in all but one isolate, with CTX-M-15 accounting for 87.8%. Among other β-lactamases, TEM-1B and OXA-1 were coproduced in 41 and 19.6% of isolates. The most common plasmid-mediated quinolone resistance genes cocarried were qnr A/B/E/S (45.3%). Ninety percent of gentamicin non-susceptible isolates harbored genes encoding AAC(3) enzymes, mainly aac(3)-IIa. Only two of 57 isolates harboring aac(6')-Ib-cr were non-susceptible to amikacin. Chromosomal mutations in genes encoding DNA gyrase and topoisomerase IV enzymes were detected in 96.2% fluoroquinolone-non-susceptible E. coli and 26.7% fluoroquinolone-non-susceptible K. pneumoniae.

CONCLUSION

Our data show that CTX-M enzymes are largely the most prevalent ESBLs in children in Qatar with a predominance of CTX-M-15. Carbapenem-sparing options to treat ESBL infections are limited, given the frequent coproduction of OXA-1 and TEM-1B enzymes and coresistance to antibiotic classes other than β-lactams.

Benefits at the nanoscale: a review of nanoparticle-enabled processes favouring microbial growth and functionality

Nanoparticles are ubiquitous and co-occur with microbial life in every environment on Earth. Interactions between microbes and nanoparticles impact the biogeochemical cycles via accelerating various reaction rates and enabling biological processes at the smallest scales. Distinct from microbe-mineral interactions at large, microbe-nanoparticle interactions may involve higher levels of active recognition and utilization of the reactive, changeable, and thereby 'moldable' nano-sized inorganic phases by microbes, which has been given minimal attention in previous reviews. Here we have compiled the various cases of microbe-nanoparticle interactions with clear and potential benefits to the microbial cells and communities. Specifically, we discussed (i) the high bioavailabilities of nanoparticles due to increased specific surface areas and size-dependent solubility, with a focus on environmentally-relevant iron(III) (oxyhydr)oxides and pyrite, (ii) microbial utilization of nanoparticles as 'nano-tools' for electron transfer, chemotaxis, and storage units, and (iii) speculated benefits of precipitating 'moldable' nanoparticles in extracellular biomineralization. We further discussed emergent questions concerning cellular level responses to nanoparticle-associated cues, and the factors that affect nanoparticles' bioavailabilities beyond size-dependent effects. We end the review by proposing a framework towards more quantitative approaches and by highlighting promising techniques to guide future research in this exciting field.

Elemental Sulfur Formation by Sulfuricurvum kujiense Is Mediated by Extracellular Organic Compounds

Elemental sulfur [S(0)] is a central and ecologically important intermediate in the sulfur cycle, which can be used by a wide diversity of microorganisms that gain energy from its oxidation, reduction, or disproportionation. S(0) is formed by oxidation of reduced sulfur species, which can be chemically or microbially mediated. A variety of sulfur-oxidizing bacteria can biomineralize S(0), either intracellularly or extracellularly. The details and mechanisms of extracellular S(0) formation by bacteria have been in particular understudied so far. An important question in this respect is how extracellular S(0) minerals can be formed and remain stable in the environment outside of their thermodynamic stability domain. It was recently discovered that S(0) minerals could be formed and stabilized by oxidizing sulfide in the presence of dissolved organic compounds, a process called S(0) organomineralization. S(0) particles formed through this mechanism possess specific signatures such as morphologies that differ from that of their inorganically precipitated counterparts, encapsulation within an organic envelope, and metastable crystal structures (presence of the monoclinic β- and γ-S₈ allotropes). Here, we investigated S(0) formation by the chemolithoautotrophic sulfur-oxidizing and nitrate-reducing bacterium Sulfuricurvum kujiense (Epsilonproteobacteria). We performed a thorough characterization of the S(0) minerals produced extracellularly in cultures of this microorganism, and showed that they present all the specific signatures (morphology, association with organics, and crystal structures) of organomineralized S(0). Using "spent medium" experiments, we furthermore demonstrated that soluble extracellular compounds produced by S. kujiense are necessary to form and stabilize S(0) minerals outside of the cells. This study provides the first experimental evidence of the importance of organomineralization in microbial S(0) formation. The prevalence of organomineralization in extracellular S(0) precipitation by other sulfur bacteria remains to be investigated, and the biological role of this mechanism is still unclear. However, we propose that sulfur-oxidizing bacteria could use soluble organics to stabilize stores of bioavailable S(0) outside the cells.

Insight Into Interactions of Thermoacidophilic Archaea With Elemental Sulfur: Biofilm Dynamics and EPS Analysis

Biooxidation of reduced inorganic sulfur compounds (RISCs) by thermoacidophiles is of particular interest for the biomining industry and for environmental issues, e.g., formation of acid mine drainage (AMD). Up to now, interfacial interactions of acidophiles with elemental sulfur as well as the mechanisms of sulfur oxidation by acidophiles, especially thermoacidophiles, are not yet fully clear. This work focused on how a crenarchaeal isolate Acidianus sp. DSM 29099 interacts with elemental sulfur. Analysis by Confocal laser scanning microscopy (CLSM) and Atomic force microscopy (AFM) in combination with Epifluorescence microscopy (EFM) shows that biofilms on elemental sulfur are characterized by single colonies and a monolayer in first stage and later on 3-D structures with a diameter of up to 100 μm. The analysis of extracellular polymeric substances (EPS) by a non-destructive lectin approach (fluorescence lectin-barcoding analysis) using several fluorochromes shows that intial attachment was featured by footprints rich in biofilm cells that were embedded in an EPS matrix consisting of various glycoconjugates. Wet chemistry data indicate that carbohydrates, proteins, lipids and uronic acids are the main components. Attenuated reflectance (ATR)-Fourier transformation infrared spectroscopy (FTIR) and high-performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) indicate glucose and mannose as the main monosaccharides in EPS polysaccharides. EPS composition as well as sugar types in EPS vary according to substrate (sulfur or tetrathionate) and lifestyle (biofilms and planktonic cells). This study provides information on the building blocks/make up as well as dynamics of biofilms of thermoacidophilic archaea in extremely acidic environments.