TABLE 3.
MeHg production in D. desulfuricans ND132 wild-type and mutant strains
| D. desulfuricans strain | Characteristic(s)a | Mean MeHg concn (pmol/ml culture) ± SD | Mean MeHg concn (pmol/mg protein) ± SD | % MeHg productionb (vs WT) | P value | Reference |
|---|---|---|---|---|---|---|
| ND132 | Wild type | 5.4 ± 1.9 | 78.1 ± 25.1 | 100 | This study | |
| JWN1001 | ND132 Δ(hgcAB)::(Pnpt-npt-upp) | <DL | <DL | <DL** | <0.005 | 12 |
| JWN1001 | ND132 Δ(hgcAB)::(Pnpt-npt-upp) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1005 | HgcAΔ(Ala166 to TGA stop codon) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1006 | HgcA(Cys93Thr) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1016 | HgcA(Cys93Ala) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1017 | HgcA(Trp92Ala) | 1.2 ± 0.2 | 16.8 ± 2.4 | 21.5 ± 3.1* | 0.014 | This study |
| JWN1018 | HgcA(Val91Ala) | 3.6 ± 0.5 | 55.8 ± 7.5 | 71.4 ± 9.6 | 0.214 | This study |
| JWN1019 | HgcA(Asn90Ala) | 7.0 ± 0.6 | 101 ± 9.2 | 129 ± 11.8 | 0.212 | This study |
| JWN1020 | HgcA(Ile89Ala) | 4.0 ± 0.5 | 61.3 ± 7.4 | 78.4 ± 9.5 | 0.329 | This study |
| JWN1021 | HgcA(Gly88Ala) | 3.4 ± 0.1 | 48.7 ± 1.3 | 62.3 ± 1.7 | 0.113 | This study |
| JWN1022 | HgcA(Arg87Ala) | 4.9 ± 0.8 | 73.2 ± 11.8 | 93.7 ± 15.1 | 0.775 | This study |
| JWN1024 | HgcA(Lys97Ala) | 4.9 ± 0.1 | 77.2 ± 2.0 | 98.8 ± 2.6 | 0.943 | This study |
| JWN1025 | HgcA(Gly98Ala) | 8.3 ± 0.5 | 118 ± 7.7 | 151 ± 9.8 | 0.058 | This study |
| JWN1026 | HgcA(Leu99Ala) | 3.3 ± 0.6 | 52.7 ± 9.0 | 67.4 ± 11.6 | 0.174 | This study |
| JWN1027 | HgcA(Phe100Ala) | 6.6 ± 0.4 | 89.1 ± 5.9 | 114 ± 7.6 | 0.501 | This study |
| JWN1028 | HgcA(Tyr101Ala) | 15.2 ± 0.8 | 192 ± 10 | 246 ± 12.8** | 0.002 | This study |
| JWN1029 | HgcA(Ala94Ser) | 8.7 ± 1.2 | 139 ± 19 | 178 ± 24.3* | 0.029 | This study |
| JWN1030 | HgcA(Ala95Ser) | 5.4 ± 1.6 | 91.7 ± 26.1 | 117 ± 33.4 | 0.551 | This study |
| JWN1031 | HgcA(Glu312Ala) | 8.9 ± 1.0 | 160 ± 19 | 205 ± 24.3* | 0.011 | This study |
| JWN1045 | HgcA(Cys93His) | 0.3 ± 0.2 | 3.8 ± 3.2 | 4.9 ± 4.1* | 0.007 | This study |
| JWN1064 | HgcA(Asn90Pro) | 1.7 ± 0.0 | 23.3 ± 0.4 | 29.8 ± 0.5* | 0.019 | This study |
| JWN1065 | HgcA(Val91Pro) | 0.4 ± 0.0 | 5.7 ± 0.7 | 7.3 ± 0.9* | 0.008 | This study |
| JWN1072 | HgcA(Ala94Pro) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1067 | HgcA(Ala95Pro) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1068 | HgcA(Trp92Pro) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1069 | HgcA(Trp92Phe) | 0.4 ± 0.0 | 6.1 ± 0.2 | 7.8 ± 0.3* | 0.008 | This study |
| JWN1066 | HgcA(Glu187Stop) | <DL | <DL | <DL** | <0.005 | This study |
| JWN1073 | HgcA(Gly98Pro) | 3.6 ± 0.3 | 54.8 ± 5.3 | 70.1 ± 6.8 | 0.191 | This study |
| JWN1013 | HgcB(Cys94Ala) | 5.5 ± 0.4 | 85.2 ± 5.9 | 109 ± 7.6 | 0.066 | This study |
| JWN1014 | HgcB(Cys95Ala) | 6.6 ± 0.7 | 94.3 ± 10 | 121 ± 13 | 0.358 | This study |
| JWN1015 | HgcB(Cys94–95Ala) | 0.2 ± 0.1 | 3.4 ± 0.9 | 4.3 ± 1.1* | 0.007 | This study |
| JWN1081 | HgcB(Cys73Ala) | <DL | <DL | <DL** | <0.005 | This study |
a
Hg methylation potentials were determined from experiments performed with mutant strains of D. desulfuricans. The standard deviations from triplicate methylation assays are displayed for each value.
b
The average production of MeHg normalized to the protein concentration was used to estimate the percentage of MeHg produced by a mutant compared to the wild type (WT). MeHg data normalized to protein data were used for statistics. <DL denotes a value below the minimum detectable limit of 45 ± 20 fmol MeHg/ml. *, P value of <0.05; **, P value of <0.005 (by an unpaired t test) (means and standard deviations are from triplicate experiments).