Syntrophic Partners Enhance Growth and Respiratory Dehalogenation of Hexachlorobenzene by Dehalococcoides mccartyi Strain CBDB1

This study investigated syntrophic interactions between chlorinated benzene respiring Dehalococcoides mccartyi strain CBDB1 and fermenting partners (Desulfovibrio vulgaris, Syntrophobacter fumaroxidans, and Geobacter lovleyi) during hexachlorobenzene respiration. Dechlorination rates in syntrophic co-cultures were enhanced 2-3 fold compared to H2 fed CBDB1 pure cultures (0.23 ± 0.04 μmol Cl− day−1). Syntrophic partners were also able to supply cobalamins to CBDB1, albeit with 3–10 fold lower resultant dechlorination activity compared to cultures receiving exogenous cyanocobalamin. Strain CBDB1 pure cultures accumulated ~1 μmol of carbon monoxide per 87.5 μmol Cl− released during hexachlorobenzene respiration resulting in decreases in dechlorination activity. The syntrophic partners investigated were shown to consume carbon monoxide generated by CBDB1, thus relieving carbon monoxide autotoxicity. Accumulation of lesser chlorinated chlorobenzene congeners (1,3- and 1,4-dichlorobenzene and 1,3,5-trichlorobenzene) also inhibited dechlorination activity and their removal from the headspace through adsorption to granular activated carbon was shown to restore activity. Proteomic analysis revealed co-culturing strain CBDB1 with Geobacter lovleyi upregulated CBDB1 genes associated with reductive dehalogenases, hydrogenases, formate dehydrogenase, and ribosomal proteins. These data provide insight into CBDB1 ecology and inform strategies for application of CBDB1 in ex situ hexachlorobenzene destruction technologies

Communication in bacteria: an ecological and evolutionary perspective

Individual bacteria can alter their behaviour through chemical interactions between organisms in microbial communities - this is generally referred to as quorum sensing. Frequently, these interactions are interpreted in terms of communication to mediate coordinated, multicellular behaviour. We show that the nature of interactions through quorum-sensing chemicals does not simply involve cooperative signals, but entails other interactions such as cues and chemical manipulations. These signals might have a role in conflicts within and between species. The nature of the chemical interaction is important to take into account when studying why and how bacteria react to the chemical substances that are produced by other bacteria

Secondary effects of antibiotics on microbial biofilms

Biofilms are assemblages of microorganisms attached to each other, or to a surface, and encased in a protective, self-produced matrix. Such associations are now recognized as the predominant microbial growth mode. The physiology of cells in biofilms differs from that of the planktonic cells on which most research has been conducted. Consequently, there are significant gaps in our knowledge of the biofilm lifestyle. Filling this gap is particularly important, given that biofilm cells may respond differently to antibiotics than do planktonic cells of the same species. Understanding the effects of antibiotics on biofilms is of paramount importance for clinical practice due to the increased levels of antibiotic resistance and resistance dissemination in biofilms. From a wider environmental perspective antibiotic exposure can alter the ecology of biofilms in nature, and hence disrupt ecosystems. Biofilm cells display increased resilience toward antibiotics. This resilience is often explained by mechanisms and traits such as decreased antibiotic penetration, metabolically inactive persister cells, and intrinsic resistance by members of the biofilm community. Together, these factors suggest that cells in biofilms are often exposed to subinhibitory concentrations of antimicrobial agents. Here we discuss how cells in biofilms are affected by the presence of antibiotics at subinhibitory concentrations, and the possible ramifications of such secondary effects for healthcare and the environment.Published versio

Novel dichloromethane-fermenting bacteria in the Peptococcaceae family

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 DCMF, the dominant organism in an anaerobic enrichment culture (DFE) 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. DCMF is the first anaerobic DCM-degrading population 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. The flux of these substrates from subsurface environments may either directly (DCM, methanol) or indirectly (choline, glycine betaine) affect the climate. Community profiling and cultivation of cohabiting taxa in culture DFE without DCMF suggest that DCMF 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 DCMF in a novel genus within the Peptococcaceae family, 'Candidatus Formimonas warabiya'

Development of a treatment solution for reductive dechlorination of hexachloro-1,3-butadiene in vadose zone soil

The biodegradation of chlorinated organics in vadose zone soils is challenging owing to the presence of oxygen, which inhibits reductive dehalogenation reactions and consequently the growth of dehalorespiring microbes. In addition, the hydraulic conductivity of vadose zone soils is typically high, hence attempts to remediate such zones with biostimulation solutions are often unsuccessful due to the short residence times for these solutions to act upon the native bacterial community. In this study we have identified sodium alginate as a hydrogel polymer that can be used to increase the residence time of a nutrient solution in an unsaturated sandy soil. Additionally we have identified neutral red as a redox active compound that can catalyse the reductive dechlorination of the chlorinated organic hexachloro-1,3-butadiene by activated sludge fed with lactate and acetate. Finally we have shown that a nutrient solution amended with neutral red and sodium alginate can lower the redox potential and reduce hexachloro-1,3-butadiene concentrations in a contaminated vadose zone soil

Whole genome sequencing of a novel, dichloromethane-fermenting Peptococcaceae from an enrichment culture

Bacteria capable of dechlorinating the toxic environmental contaminant dichloromethane (DCM, CH2Cl2) are of great interest for potential bioremediation applications. A novel, strictly anaerobic, DCM-fermenting bacterium, "DCMF'', was enriched from organochlorine-contaminated groundwater near Botany Bay, Australia. The enrichment culture was maintained in minimal, mineral salt medium amended with dichloromethane as the sole energy source. PacBio whole genome SMRT (TM) sequencing of DCMF allowed de novo, gap-free assembly despite the presence of cohabiting organisms in the culture. Illumina sequencing reads were utilised to correct minor indels. The single, circularised 6.44 Mb chromosome was annotated with the IMG pipeline and contains 5,773 predicted protein-coding genes. Based on 16S rRNA gene and predicted proteome phylogeny, the organism appears to be a novel member of the Peptococcaceae family. The DCMF genome is large in comparison to known DCM-fermenting bacteria. It includes an abundance of methyltransferases, which may provide clues to the basis of its DCM metabolism, as well as potential to metabolise additional methylated substrates such as quaternary amines. Full annotation has been provided in a custom genome browser and search tool, in addition to multiple sequence alignments and phylogenetic trees for every predicted protein, http://www.slimsuite.unsw.edu.au/research/dcmf/

Evaluation of hindered amine light stabilisers and their N-chlorinated derivatives as antibacterial and antifungal additives for thermoset surface coatings

N-Halogenated amines or ‘halamines’ have attracted recent attention as potential biocides for materi-als and surface coatings application. Facile N-chlorination of the hindered amine light stabiliser (HALS)Tinuvin®770, bis-(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, was achieved by reaction with sodiumdichloroisocyanurate. The chlorinated product was incorporated into a polyester-based paint formulatedfor coil coating, applied to test panels and subjected to high temperature curing conditions characteristicof the coil coating process (55 s at 262◦C). Rapid detection of N-chlorinated Tinuvin®770 in the curedcoating was confirmed, using liquid extraction surface analysis-mass spectrometry, by the characteris-tic fragmentation patterns of the halamines observed upon collision-induced dissociation. Antimicrobialactivity of the coating was determined by testing against the bacterium Pseudomonas aeruginosa and thefungus Cladosporium sp., two organisms that are known to colonise both internal and external surfaces inbuilding and cladding applications. The activity of HALS and halamine containing coatings were comparedagainst a commercial product containing an antimicrobial additive as well as control surfaces withoutadditives. Significant activity against the bacterium, but not against the fungus was demonstrated forthe parent HALS and halamine containing coatings. The possibility of regeneration of the halamines wasalso tested and confirmed by mass spectrometry, post-chlorination of samples showed no significantdifferences in activity between corresponding pairs of samples