The complete genome of 2,6-dichlorobenzamide (BAM) degrader Aminobacter sp. MSH1 suggests a polyploid chromosome, phylogenetic reassignment, and functions of plasmids.

Aminobacter sp. MSH1 (CIP 110285) can use the pesticide dichlobenil and its recalcitrant transformation product, 2,6-dichlorobenzamide (BAM), as sole source of carbon, nitrogen, and energy. The concentration of BAM in groundwater often exceeds the threshold limit for drinking water, requiring additional treatment in drinking water treatment plants or closure of the affected abstraction wells. Biological treatment with MSH1 is considered a potential sustainable alternative to remediate BAM-contamination in drinking water production. We present the complete genome of MSH1, which was determined independently in two institutes at Aarhus University and KU Leuven. Divergences were observed between the two genomes, i.e. one of them lacked four plasmids compared to the other. Besides the circular chromosome and the two previously described plasmids involved in BAM catabolism, pBAM1 and pBAM2, the genome of MSH1 contained two megaplasmids and three smaller plasmids. The MSH1 substrain from KU Leuven showed a reduced genome lacking a megaplasmid and three smaller plasmids and was designated substrain MK1, whereas the Aarhus variant with all plasmids was designated substrain DK1. A plasmid stability experiment indicate that substrain DK1 may have a polyploid chromosome when growing in R2B medium with more chromosomes than plasmids per cell. Finally, strain MSH1 is reassigned as Aminobacter niigataensis MSH1.

Two novel bacteriophage genera from a groundwater reservoir highlight subsurface environments as underexplored biotopes in bacteriophage ecology.

Although bacteriophages are central entities in bacterial ecology and population dynamics, there is currently no literature on the genomes of bacteriophages isolated from groundwater. Using a collection of bacterial isolates from an aquifer as hosts, this study isolated, sequenced and characterised two bacteriophages native to the groundwater reservoir. Host phylogenetic analyses revealed that the phages targeted B. mycoides and a novel Pseudomonas species. These results suggest that both bacteriophages represent new genera, highlighting that groundwater reservoirs, and probably other subsurface environments as well, are underexplored biotopes in terms of the presence and ecology of bacteriophages.

A novel hybrid concept for implementation in drinking water treatment targets micropollutant removal by combining membrane filtration with biodegradation.

Groundwater extracted for drinking water production is commonly treated by aeration and sand filtration. However, this simple treatment is typically unable to remove pesticide residues. As a solution, bioaugmentation of sand filter units (i.e., the addition of specific degrader strains) has been proposed as an alternative "green" technology for targeted pesticide removal. However, the introduced degraders are challenged by (i) micropollutant levels of target residue, (ii) the oligotrophic environment and (iii) competition and predation by the native microorganisms, leading to loss of population and degradation potential. To overcome these challenges, we propose the introduction of a novel hybrid treatment step to the overall treatment process in which reverse osmosis filtration and biodegradation are combined to remove a target micropollutant. Here, the reverse osmosis produces a concentrated retentate that will act as a feed to a dedicated biofilter unit, intended to promote biodegradation potential and stability of an introduced degrader. Subsequently, the purified retentate will be re-mixed with the permeate from reverse osmosis, for re-mineralization and downstream consumption. In our study, we investigated the effect of reverse osmosis retentates on the degradation potential of an introduced degrader. This paper provides the first promising results of this hybrid concept using the 2,6-dichlorobenzamide (BAM)-degrading bacteria Aminobacter sp. MSH1 in batch experiments, spiked with radiolabeled BAM. The results showed an increased degradation potential of MSH1 in retentate waters versus untreated water. Colony-forming units and qPCR showed a stable MSH1 population, despite higher concentrations of salts and metals, and increased growth of native bacteria.

An intriguing relationship between the cyclic diguanylate signaling system and horizontal gene transfer.

The second messenger cyclic diguanylate (c-di-GMP) is ubiquitously used by bacteria to modulate and shift between different phenotypes including motility, biofilm formation and virulence. Here we show that c-di-GMP-associated genes are widespread on plasmids and that enzymes that synthesize or degrade c-di-GMP are preferentially encoded on transmissible plasmids. Additionally, expression of enzymes that synthesize c-di-GMP was found to increase both biofilm formation and, interestingly, conjugative plasmid transfer rates.