Nadia Morson, Olivia Molenda, Katherine J Picott, Ruth E Richardson, Elizabeth A Edwards
{"title":"Long-term survival of <i>Dehalococcoides mccartyi</i> strains in mixed cultures under electron acceptor and ammonium limitation.","authors":"Nadia Morson, Olivia Molenda, Katherine J Picott, Ruth E Richardson, Elizabeth A Edwards","doi":"10.1093/femsmc/xtac021","DOIUrl":null,"url":null,"abstract":"<p><p>Few strains of <i>Dehalococcoides mccartyi</i> harbour and express the vinyl chloride reductase (VcrA) that catalyzes the dechlorination of vinyl chloride (VC), a carcinogenic soil and groundwater contaminant. The <i>vcrA</i> operon is found on a Genomic Island (GI) and, therefore, believed to participate in horizontal gene transfer (HGT). To try to induce HGT of the <i>vcrA</i>-GI, we blended two enrichment cultures in medium without ammonium while providing VC. We hypothesized that these conditions would select for a mutant strain of <i>D. mccartyi</i> that could both fix nitrogen and respire VC. However, after more than 4 years of incubation, we found no evidence for HGT of the <i>vcrA</i>-GI. Rather, we observed VC-dechlorinating activity attributed to the trichloroethene reductase TceA. Sequencing and protein modelling revealed a mutation in the predicted active site of TceA, which may have influenced substrate specificity. We also identified two nitrogen-fixing <i>D. mccartyi</i> strains in the KB-1 culture. The presence of multiple strains of <i>D. mccartyi</i> with distinct phenotypes is a feature of natural environments and certain enrichment cultures (such as KB-1), and may enhance bioaugmentation success. The fact that multiple distinct strains persist in the culture for decades and that we could not induce HGT of the <i>vcrA</i>-GI suggests that it is not as mobile as predicted, or that mobility is restricted in ways yet to be discovered to specific subclades of <i>Dehalococcoides</i>.</p>","PeriodicalId":73024,"journal":{"name":"FEMS microbes","volume":"3 ","pages":"xtac021"},"PeriodicalIF":0.0000,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10117805/pdf/","citationCount":"1","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"FEMS microbes","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1093/femsmc/xtac021","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 1
Abstract
Few strains of Dehalococcoides mccartyi harbour and express the vinyl chloride reductase (VcrA) that catalyzes the dechlorination of vinyl chloride (VC), a carcinogenic soil and groundwater contaminant. The vcrA operon is found on a Genomic Island (GI) and, therefore, believed to participate in horizontal gene transfer (HGT). To try to induce HGT of the vcrA-GI, we blended two enrichment cultures in medium without ammonium while providing VC. We hypothesized that these conditions would select for a mutant strain of D. mccartyi that could both fix nitrogen and respire VC. However, after more than 4 years of incubation, we found no evidence for HGT of the vcrA-GI. Rather, we observed VC-dechlorinating activity attributed to the trichloroethene reductase TceA. Sequencing and protein modelling revealed a mutation in the predicted active site of TceA, which may have influenced substrate specificity. We also identified two nitrogen-fixing D. mccartyi strains in the KB-1 culture. The presence of multiple strains of D. mccartyi with distinct phenotypes is a feature of natural environments and certain enrichment cultures (such as KB-1), and may enhance bioaugmentation success. The fact that multiple distinct strains persist in the culture for decades and that we could not induce HGT of the vcrA-GI suggests that it is not as mobile as predicted, or that mobility is restricted in ways yet to be discovered to specific subclades of Dehalococcoides.