Comparative analysis of microbial communities from different full-scale haloalkaline biodesulfurization systems

Abstract

In biodesulfurization (BD) at haloalkaline and dO₂-limited conditions, sulfide-oxidizing bacteria (SOB) effectively convert sulfide into elemental sulfur that can be used in agriculture as a fertilizer and fungicide. Here we show which bacteria are present in this biotechnological process. 16S rRNA gene amplicon sequencing of biomass from ten reactors sampled in 2018 indicated the presence of 444 bacterial Amplicon Sequence Variants (ASVs). A core microbiome represented by 30 ASVs was found in all ten reactors, with Thioalkalivibrio sulfidiphilus as the most dominant species. The majority of these ASVs are phylogenetically related to bacteria previously identified in haloalkaline BD processes and in natural haloalkaline ecosystems. The source and composition of the feed gas had a great impact on the microbial community composition followed by alkalinity, sulfate, and thiosulfate concentrations. The halophilic SOB of the genus Guyparkeria (formerly known as Halothiobacillus) and heterotrophic SOB of the genus Halomonas were identified as potential indicator organisms of sulfate and thiosulfate accumulation in the BD process.

Key points

• Biodesulfurization (BD) reactors share a core microbiome

• The source and composition of the feed gas affects the microbial composition in the BD reactors

• Guyparkeria and Halomonas indicate high concentrations of sulfate and thiosulfate in the BD process

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11771-y.

Sodium Energetic Cycle in the Natronophilic Bacterium Thioalkalivibrio versutus

As inhabitants of soda lakes, Thioalkalivibrio versutus are halo- and alkaliphilic bacteria that have previously been shown to respire with the first demonstrated Na⁺-translocating cytochrome-c oxidase (CO). The enzyme generates a sodium-motive force (Δs) as high as −270 mV across the bacterial plasma membrane. However, in these bacteria, operation of the possible Δs consumers has not been proven. We obtained motile cells and used them to study the supposed Na⁺ energetic cycle in these bacteria. The resulting motility was activated in the presence of the protonophore 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), in line with the same effect on cell respiration, and was fully blocked by amiloride—an inhibitor of Na⁺-motive flagella. In immotile starving bacteria, ascorbate triggered CO-mediated respiration and motility, both showing the same dependence on sodium concentration. We concluded that, in T. versutus, Na⁺-translocating CO and Na⁺-motive flagella operate in the Na⁺ energetic cycle mode. Our research may shed light on the energetic reason for how these bacteria are confined to a narrow chemocline zone and thrive in the extreme conditions of soda lakes.

A review of the defining chemical properties of soda lakes and pans: An assessment on a large geographic scale of Eurasian inland saline surface waters

The aim of this study is to evaluate the definition of water chemical type, with particular attention to soda brine characteristics by assessing ionic composition and pH values on a large geographic scale and broad salinity (TDS) range of Eurasian inland saline surface waters, in order to rectify the considerable confusion about the exact chemical classification of soda lakes and pans. Data on pH and on the concentration of eight major ions were compiled into a database drawn from Austria, China, Hungary, Kazakhstan, Mongolia, Russia, Serbia, and Turkey. The classification was primarily based on dominant ions exceeding an equivalent percentage of 25 (> 25e%) of the total cations or anions, and the e% rank of dominant ions was also identified. We identified four major types: waters dominated by (1) Na-HCO₃ (10.0%), (2) Na-HCO₃ + CO₃ (31.4%), (3) Na-Cl (45.9%), and (4) Na-SO₄ (12.7%), considering only the first ion by e% rank. These major types can be divided into 30 subtypes in the dataset, taking into account the e% rank of all dominant ions. The major and subtypes of soda brine can be divided into “Soda” and “Soda-Saline” types. “Soda type” when Na⁺ and HCO₃^– + CO₃^2– are the first in the rank of dominant ions (> 25e%), and “Soda-Saline type” when Na⁺ is the first in the rank of dominant cations and the sum of HCO₃^– + CO₃^2– concentration exceeds 25e%, but it is not the first in the rank of dominant anions. Soda-saline type can be considered as a separate evolutionary stage between Soda and Saline types respect to the geochemical interpretation by saturation indexes of brines. The obtained overlapping ranges in distribution demonstrate that a pH measurement alone is not a reliable indicator to classify the permanent alkaline “soda type” and various other types of temporary alkaline waters.