Biology subjects

Macalady, J. L.

Publications and source records attributed to Macalady, J. L..

4 recordsLinked to original sources

bioRxiv2023

Isolation of a putative sulfur comproportionating microorganism

Sulfur comproportionation is a heretofore undiscovered microbial catabolism that was predicted based on thermodynamic calculations. Here, we report the isolation of an Acidithiobacillus thiooxidans strain from extremely low pH snottite biofilms in the karst at Frasassi, Italy. The strain grew to cell densities of >107 cells mL-1 in autotrophic sulfur comproportionation medium. Whole genome sequencing of the isolate revealed the presence of numerous genes involved in sulfur transformations that could be linked in a sulfur comproportionation pathway. We describe an experimental framework, including measurements of sulfate, sulfide, and S0 concentrations, electron microscopy, and stable and radioisotope incubations coupled with NanoSIMS, scintillation counting and isotope ratio mass spectrometry, for future searches of sulfur comproportionators. SignificanceThe prediction of and search for novel microbial catabolic reactions can be streamlined by using thermodynamics to identify energy-yielding redox reactions that may be catalyzed by microorganisms. This strategy has been used to successfully predict several previously overlooked microbial catabolic reactions, including anaerobic ammonia oxidation (anammox), anaerobic oxidation of methane (AOM), and complete ammonia oxidation (comammox). Sulfur comproportionation, or the coupled reduction of sulfate and oxidation of sulfide to form elemental sulfur, was predicted by thermodynamic calculations to exist as a microbial catabolism in low pH, low-temperature environments. In this study, we describe the isolation of the first putative sulfur comproportionating microorganism and provide a detailed experimental approach that can be applied to future investigations of this novel link in the biogeochemical sulfur cycle.

microbiology↗

bioRxiv2023

Sulfur disproportionating microbial communities in a dynamic, microoxic-sulfidic karst system

Biogeochemical sulfur cycling in sulfidic karst systems is largely driven by abiotic and biological sulfide oxidation, but the fate of elemental sulfur (S0) that accumulates in these systems is not well understood. The Frasassi Cave system (Italy) is intersected by a sulfidic aquifer that mixes with small quantities of oxygen-rich meteoric water, creating Proterozoic-like conditions and supporting a prolific ecosystem driven by sulfur-based chemolithoautotrophy. To better understand the cycling of S0 in this environment, we examined the geochemistry and microbiology of sediments underlying widespread sulfide-oxidizing mats dominated by Beggiatoa. Sediment populations were dominated by uncultivated relatives of sulfur cycling chemolithoautotrophs related to Sulfurovum, Halothiobacillus, Thiofaba, Thiovirga, Thiobacillus, and Desulfocapsa, as well as diverse uncultivated anaerobic heterotrophs affiliated with Bacteroidota, Anaerolineaceae, Lentimicrobiaceae, and Prolixibacteraceae. Desulfocapsa and Sulfurovum populations accounted for 12-26% of sediment 16S rRNA amplicon sequences and were closely related to isolates which carry out autotrophic S0 disproportionation in pure culture. Gibbs energy ({Delta}Gr) calculations revealed that S0 disproportionation under in situ conditions is energy yielding. Microsensor profiles through the mat-sediment interface showed that Beggiatoa mats consume dissolved sulfide and oxygen, but a net increase in acidity was only observed in the sediments below. Together, these findings suggest that disproportionation is an important sink for S0 generated by microbial sulfide oxidation in this oxygen-limited system and may contribute to the weathering of carbonate rocks and sediments in sulfur- rich environments.

microbiology↗

bioRxiv2022

Thiovibrio frasassiensis gen. nov., sp. nov., an autotrophic, elemental sulfur disproportionating bacterium isolated from sulfidic karst sediment, and proposal of Thiovibrionaceae fam. nov.

A novel, autotrophic, mesophilic bacterium, strain RS19-109T, was isolated from sulfidic stream sediments in the Frasassi Caves, Italy. The cells of this strain grew chemolithoautotrophically under anaerobic conditions while disproportionating elemental sulfur (S0) and thiosulfate, but not sulfite with bicarbonate/CO2 as a carbon source. Autotrophic growth was also observed with molecular hydrogen as an electron donor, and S0, sulfate, thiosulfate, nitrate, and ferric iron as electron acceptors. Oxygen was not used as an electron acceptor and sulfide was not used as an electron donor. Weak growth was observed with sulfate as an electron acceptor and organic carbon as electron donors and carbon sources. The strain also showed weak growth by fermentation of tryptone. Strain RS19-109T was found to be phylogenetically distinct based on 16S rRNA gene sequence similarity (89.2%) to its closest relative, Desulfurivibrio alkaliphilus AHT2T. The draft genome sequence for strain RS19-109T had average nucleotide identity, average amino acid identity, and in silico DNA-DNA hybridization values of 72.2%, 63.0%, and 18.3%, respectively, compared with the genome sequence of D. alkaliphilus AHT2T. On the basis of its physiological and genomic properties, strain RS19-109T is proposed as the type strain of a novel species of a novel genus, Thiovibrio frasassiensis gen. nov., sp. nov. A novel family, Thiovibrionaceae fam. nov., is proposed to accommodate Thiovibrio within the order Desulfobulbales.

microbiology↗

bioRxiv2021

Organic stabilization of extracellular elemental sulfur in a Sulfurovum-rich biofilm: a new role for EPS?

This work shines light on the role of extracellular polymeric substances (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 (-S8) and metastable ({beta}-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 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.

microbiology↗