Enumeration of Chemoorganotrophic Carbonyl Sulfide (COS)-degrading Microorganisms by the Most Probable Number Method

Abstract

Carbonyl sulfide (COS) is the most abundant sulfur compound in the atmosphere, and, thus, is important in the global sulfur cycle. Soil is a major sink of atmospheric COS and the numerical distribution of soil microorganisms that degrade COS is indispensable for estimating the COS-degrading potential of soil. However, difficulties are associated with counting COS-degrading microorganisms using culture-dependent approaches, such as the most probable number (MPN) method, because of the chemical hydrolysis of COS by water. We herein developed a two-step MPN method for COS-degrading microorganisms: the first step for chemoorganotrophic growth that supported a sufficient number of cells for COS degradation in the second step. Our new MPN analysis of various environmental samples revealed that the cell density of COS-degrading microorganisms in forest soils ranged between 10 6 and 10 8 MPN (g dry soil) -1 , which was markedly higher than those in volcanic deposit and water samples, and strongly correlated with the rate of COS degradation in environmental samples. Numerically dominant COS degraders that were isolated from the MPN-positive culture were related to bacteria in the orders Bacillales and Actinomycetales. The present results provide numerical evidence for the ubiquity of COSdegrading microbes in natural environments.

QM study of carbon dioxide (CO2) and carbonyl sulfide (COS) degradation by cluster model of Carbonic anhydrase enzyme

“…The average distance between Zn 2+ and N atom in histidine is 2.07 Å that is in good agreement with X-ray crystallography data, 2.11 Å. Comparison between theoretical and X-ray [47] data indicates that the standard deviation of bond distance is about 0.07 for ACAII and 0.13 for ICAII respectively in water phase, Table 1. Also the average N (His) -Zn -O(OH 2 or OH) and N(His) -Zn -N(His) bond angles is equal to 114.79 • that shows tetrahedral geometry.…”

“…The additional step includes the release of the bicarbonate ion (HCO 3 − ) facilitated by the entrance of another water molecule, that will be deprotonated to reproduce the active catalyst. Also, the role of carbonic anhydrase enzyme in the regulation and fixation of the atmospheric trace gas carbonyl sulfide, COS, has been less investigated [37,[45][46][47]. Carbonyl sulfide is the most stable reduced sulfur compound in the troposphere, which plays a key role in the global distribution of sulfur.…”

Fungal Carbonyl Sulfide Hydrolase of <i>Trichoderma harzianum</i> Strain THIF08 and Its Relationship with Clade D β-Carbonic Anhydrases

“…The COSase of T. harzianum strain THIF08 belongs to clade D in β-CA family enzymes, and amino acids at the predicted active site of COSase, including Cys36, His88, and Cys91, which are zinc ion coordinate residues ( Rowlett, 2010 ), are also conserved in other fungal clade D β-CA family enzymes ( Table S4 ). Similar active site amino acid sequences were also found in prokaryotic clade D β-CA family enzymes ( Kato et al , 2008 ; Smeulders et al , 2011 , 2013 ; Ogawa et al , 2016 ; Kato et al , 2020 ). CA is indispensable in many biological processes, such as CO 2 fixation, respiration, and pH regulation, and the dominant CAs in bacteria and fungi belong to the β-CA family ( Smith et al , 1999 ; Smith and Ferry, 2000 ; Elleuche and Pöggeler, 2010 ).…”

“…Although CO 2 hydration activity is markedly weaker than those of β-CA family members, a comparison of amino acid sequences revealed that the COSase of strain THI115 belongs to the clade D cluster of the phylogenetic tree in the β-CA family ( Ogawa et al , 2013 ). Not only chemolithotrophic sulfur bacteria, but also various bacteria belonging to the phylum Actinobacteria were found to have the amino acid sequences of clade D β-CA family enzymes, suggesting the importance of Actinobacteria in the degradation of COS in soil environments ( Ogawa et al , 2016 ; Kato et al , 2020 ).…”

Sulfur assimilation using gaseous carbonyl sulfide by the soil fungus Trichoderma harzianum

“…In plant leaves, gaseous COS is degraded by the side reaction of enzymes that interact with CO 2 , such as RuBisCO or carbonic anhydrases (CA) during photosynthesis ( 15 – 17 ), although the physiological role of this reaction is unknown. In addition, a variety of bacteria and fungi can degrade COS ( 18 – 21 ); however, their physiological role is still unknown, except in relation to the energy metabolism of chemolithoautotrophic sulfur oxidation: Thiobacillus thioparus ( T. thioparus hereafter) strain THI115 possesses COS hydrolase (COSase, COS + H 2 O → CO 2 + H 2 S), which is clade D of the β-class CA (β-D-CA) subfamily enzyme with high specificity for COS but low activity for CO 2 hydration, and COS is degraded by COSase into H 2 S and further converted into sulfate to be an end product of energy production in the chemolithotrophic metabolism system ( 18 , 22 ). On the other hand, COS-degrading activity involving β-D-CA ( 19 – 21 ) has been reported in many heterotrophic bacteria and fungi, but the physiological role of COS degradation is unknown.…”