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

Abstract

Elemental sulfur (S 0 ) is produced and degraded by phylogenetically diverse groups of microorganisms. For Chlorobaculum tepidum , an anoxygenic phototroph, sulfide is oxidized to produce extracellular S 0 globules, which can be further oxidized to sulfate. While some sulfur-oxidizing bacteria (e.g., Allochromatium vinosum ) are also capable of growth on commercial S 0 as an electron donor, C. tepidum is not. Even colloidal sulfur sols, which appear indistinguishable from biogenic globules, do not support the growth of C. tepidum . Here, we investigate the properties that make biogenic S 0 globules distinct from abiotic forms of S 0 . We found that S 0 globules produced by C. tepidum and abiotic S 0 sols are quite similar in terms of mineralogy and material properties, but the two are distinguished primarily by the properties of their surfaces. C. tepidum ’s globules are enveloped by a layer of organics (protein and polysaccharides), which results in a surface that is fundamentally different from that of abiotic S 0 sols. The organic coating on the globules appears to slow the aging and crystallization of amorphous sulfur, perhaps providing an extended window of time for microbes in the environment to access the more labile forms of sulfur as needed. Overall, our results suggest that the surface of biogenic S 0 globules may be key to cell–sulfur interactions and the reactivity of biogenic S 0 in the environment.

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

“…However, on the sulfur surface after incubation with cells similar functional groups as on cell surfaces were detectable, namely, amide (I) and (II) and polysaccharides (Supplementary Figure S3, red line). To clarify whether these compounds on S 0 surfaces are excreted actively by cells or incidental by physical-chemical adsorption (Marnocha et al, 2019) further studies are needed.…”

“…The biogenic sulfur globules produced by cells of C. tepidum are enveloped by a layer of proteins and polysaccharides. In addition, these sulfur globules possess reactive surfaces and thus are bioavailable for microbial degradation (Marnocha et al, 2016, 2019). We assume that S 0 intermediate in the culture of Acidianus sp.…”

“…This change is probably due to the formation of a biofilm and EPS (Li and Sand, 2017). Nevertheless, further analysis is needed to verify this assumption of active microbial excretion of organic compounds on the S 0 surfaces, e.g., by Raman spectroscopy, as it is suitable and has been successfully used for analysis of S 0 and S 0 covered with biofilms and an EPS matrix (Marnocha et al, 2019).…”

A biochemical view on the biological sulfur cycle

“…A large portion of sulfur oxidizers form sulfur deposits as intermediates, both extracellularly and intracellularly (Dahl, 2020;Marnocha et al, 2016Marnocha et al, , 2019. Formation of extracellular sulfur globules is typical for green sulfur bacteria and even name-giving for sulfur oxidizers of the gammaproteobacterial family Ectothiorhodospiraceae while intracellular sulfur globules typically occur in magnetotactic sulfur oxidizers, in purple sulfur bacteria of the family Chromatiaceae and in sulfur oxidizing bacterial endosymbionts (Dahl, 2020).…”

“…Extracellular biogenic sulfur globules have properties clearly distinguishing them from abiotic elemental sulfur, such that the green sulfur bacterium C. tepidum can grow on self-produced sulfur globules but other forms of elemental sulfur do not support growth. In this case, the biogenic sulfur globules are enveloped by a layer of proteins and polysaccharides that enables cell-sulfur interactions and probably keeps the sulfur in a bioavailable form (Marnocha et al, 2019).…”