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Holland, S. I.

Publications and source records attributed to Holland, S. I..

2 recordsLinked to original sources
bioRxiv2021

Dehalobium species implicated in 2,3,7,8-tetrachloro-p-dioxin dechlorination in the contaminated sediments of Sydney Harbour Estuary

Polychlorinated dibenzo-p-dioxins and furans (PCDD/F) are some of the most environmentally recalcitrant and toxic compounds. They are naturally occurring and by-products of anthropogenic activity. Sydney Harbour Estuary (Sydney, Australia), is heavily contaminated with PCDD/F. Analysis of sediment cores revealed that the contamination source in Homebush Bay continues to have one of the highest levels of PCDD/F contamination in the world (5207 pg WHO-TEQ g-1) with >50% of the toxicity attributed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) the most toxic and concerning of the PCDD/F congeners. Comparison of congener profiles at the contamination source with surrounding bays and historical data provided evidence for the attenuation of 2,3,7,8-TCDD and other congeners at the source. This finding was supported by the detection of di-, mono- and unchlorinated dibenzo-p-dioxin. Microbial community analysis of sediments by 16S amplicon sequencing revealed an abundance of lineages from the class Dehalococcoidia (up to 15% of the community), including the genus Dehalobium (up to 0.5%). Anaerobic seawater enrichment cultures using perchloroethene as a more amenable growth substrate enriched only the Dehalobium population by more than six-fold. The enrichment culture then proved capable of reductively dechlorinating 2,3,7,8-TCDD to 2,3,7-TCDD and octachlorodibenzo-p-dibenzodioxin to hepta and hexa congeners. This work is the first to show microbial reductive dehalogenation of 2,3,7,8-TCDD with a bacterium from outside the Dehalococcoides genus, and one of only a few that demonstrates PCDD/F degradation in a marine environment.

microbiology↗
bioRxiv2020

A novel, dichloromethane-fermenting bacterium in the Peptococcaceae family, 'Candidatus Formamonas warabiya', gen. nov. sp. nov.

Dichloromethane (DCM; CH2Cl2) is a toxic groundwater pollutant that also has a detrimental effect on atmospheric ozone levels. As a dense non-aqueous phase liquid, DCM migrates vertically through groundwater to low redox zones, yet information on anaerobic microbial DCM transformation remains scarce due to a lack of cultured organisms. We report here the characterisation of strain DCMF, the dominant organism in an anaerobic enrichment culture (DFE) that is capable of fermenting DCM to the environmentally benign product acetate. Stable carbon isotope experiments demonstrated that the organism assimilated carbon from DCM and bicarbonate via the Wood-Ljungdahl pathway. Strain DCMF is the first anaerobic DCM-degrading bacterium also shown to metabolise non-chlorinated substrates. It appears to be a methylotroph utilising the Wood-Ljungdahl pathway for metabolism of methyl groups from methanol, choline, and glycine betaine, which has implications for the flux of climate-active compounds from subsurface environments. Community profiling and enrichment of the cohabiting taxa in culture DFE to the exclusion of strain DCMF suggest that it is the sole organism in this culture responsible for substrate metabolism, while the cohabitants persist via necromass recycling. Genomic and physiological evidence support placement of strain DCMF in a novel genus, Candidatus Formamonas warabiya.

microbiology↗