Abstract
Thiocyanate (N=C-S-) is a moderately toxic, inorganic sulfur compound. It occurs naturally as a by-product of the degradation of glucosinolate-containing plants and is produced industrially in a number of mining processes. Currently, two pathways for the primary degradation of thiocyanate in bacteria are recognized, the carbonyl sulfide pathway and the cyanate pathway, of which only the former has been fully characterized. Use of the cyanate pathway has been shown in only 10 strains of Thioalkalivibrio, a genus of obligately haloalkaliphilic sulfur-oxidizing Gammaproteobacteria found in soda lakes. So far, only the key enzyme in this reaction, thiocyanate dehydrogenase (TcDH), has been purified and studied. To gain a better understanding of the other genes involved in the cyanate pathway, we conducted a transcriptomics experiment comparing gene expression during the growth of Thioalkalivibrio thiocyanoxidans ARh 2T with thiosulfate with that during its growth with thiocyanate. Triplicate cultures were grown in continuous substrate-limited mode, followed by transcriptome sequencing (RNA-Seq) of the total mRNA. Differential expression analysis showed that a cluster of genes surrounding the gene for TcDH were strongly upregulated during growth with thiocyanate. This cluster includes genes for putative copper uptake systems (copCD, ABC-type transporters), a putative electron acceptor (fccAB), and a two-component regulatory system (histidine kinase and a σ54-responsive Fis family transcriptional regulator). Additionally, we observed the increased expression of RuBisCO and some carboxysome shell genes involved in inorganic carbon fixation, as well as of aprAB, genes involved in sulfite oxidation through the reverse sulfidogenesis pathway. IMPORTANCE Thiocyanate is a moderately toxic and chemically stable sulfur compound that is produced by both natural and industrial processes. Despite its significance as a pollutant, knowledge of the microbial degradation of thiocyanate is very limited. Therefore, investigation of thiocyanate oxidation in haloalkaliphiles such as the genus Thioalkalivibrio may lead to improved biotechnological applications in wastewater remediation.
Highlights
Thiocyanate (NϭCϪSϪ) is a moderately toxic, inorganic sulfur compound
We described the results of a comparative analysis of a cluster of genes surrounding the gene for thiocyanate dehydrogenase (TcDH) that is found in 10 Thioalkalivibrio strains in two different gene configurations, it remains unknown whether this cluster has an actual role in thiocyanate metabolism [18]
It should be noted that the nitrogen contents of the two different chemostat conditions were partially different: 10 mM cyanate was formed as a result of thiocyanate oxidation, which would potentially form 10 mM ammonia by spontaneous hydrolytic degradation, which is twice the amount of ammonia present in thiosulfate-fed cultures
Summary
Thiocyanate (NϭCϪSϪ) is a moderately toxic, inorganic sulfur compound It occurs naturally as a by-product of the degradation of glucosinolatecontaining plants and is produced industrially in a number of mining processes. The dominant group of chemolithotrophic SOB found in soda lakes worldwide belongs to the genus Thioalkalivibrio (family Ectothiorhodospiraceae, class Gammaproteobacteria) They are obligate haloalkaliphiles with the ability to metabolize a diverse set of reduced sulfur compounds, including sulfide, polysulfide, elemental sulfur, thiosulfate, and tetrathionate, over a broad salinity range [8]. The enzyme responsible for the reaction is a periplasmic 56-kDa copper-containing oxidoreductase named thiocyanate dehydrogenase (TcDH) The presence of this gene has so far only been reported in the genomes of 10 Thioalkalivibrio species [18], as well as that of Thiohalobacter thiocyanaticus FOKN1 [19]. We described the results of a comparative analysis of a cluster of genes surrounding the gene for TcDH that is found in 10 Thioalkalivibrio strains in two different gene configurations, it remains unknown whether this cluster has an actual role in thiocyanate metabolism [18]
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