Anode surface bioaugmentation enhances deterministic biofilm assembly in microbial fuel cells

Microbial fuel cells (MFCs) are devices that can generate energy while aiding biodegradation of waste through the activity of an electroactive mixed biofilm. Metabolic cooperation is considered essential for MFCs’ efficiency, especially during early-anode colonization. Yet, the specific ecological processes that drive the assembly of an optimized anode-attached community remain unknown. Here, we show, using 16S rRNA gene amplicon and shotgun metagenomic sequencing that bioaugmentation of the anode surface with an electroactive consortium originating from a well-established anodic biofilm, dominated by different Desulfuromonas strains, resulted in an extremely rapid voltage generation (reaching maximal voltage within several hours). This was in sharp contrast to the highly stochastic and slower biofilm assembly that occurred when the anode-surface was not augmented. By comparing two inoculation media, wastewater and filtered wastewater, we were able to illustrate two different "source-communities" for newly arriving species that with time colonized the anode surface in a different manner and resulted in dramatically different community assembly processes. Remarkably, an efficient anode colonization process was obtained only if unfiltered wastewater was added, leading to a near-complete replacement of the bioaugmented community by Geobacter lovleyi. We propose that anode bioaugmentation reduced stochasticity by creating available niches that were quickly occupied by specific newly-arriving species that positively supported the fast establishment of a highly-functional anode biofilm.

Effects of combined treatments of zinc and pH on attached bacterial abundance and activity

The response of attached bacteria to Zn at three pH levels was studied in outdoor stream mesocosms. Streams containing water from Crooked Lake, Indiana, were dosed with either 0.1 or 0.5 mg Zn/L at ambient pH (pH 8.4), pH 7.0, or pH 5.5. Samples were taken at 2, 5, 10, and 20 days and analyzed for total biomass, chlorophyll content, total bacterial numbers, and heterotrophic activity. All measures of community abundance and activity were highest in the treatment receiving 0.1 mg/L at a pH of 8.4. Treatments at lower pH levels and the higher Zn concentration showed significantly lower biomass, chlorophyll content, and total bacterial numbers. Bacterial heterotrophic activity did not demonstrate a statistically significant response as pH decreased, although it did show a statistically significant decrease at a concentration of 0.5 mg Zn/L. The portion of the bacterial community able to grow on nutrient agar demonstrated adaptation to the increased toxicity of Zn at lower pH levels by an increase in the proportion of bacteria resistant to Zn. In addition, the structure of the culturable bacterial community was altered at low pH, as demonstrated by a reduction in the Shannon–Wiener diversity index. The results indicate that pH can modulate Zn toxicity to the attached community. Key words: attached bacteria, zinc, heavy metal resistance, acid rain, species diversity.

Further Observations on the Practice of Community Care in Salford

Differences in the clinical characteristics of clients have not been found to account for the interprofessional differences in community psychiatric nurses' and mental health social workers' practice in Salford. We found the consultant-attached mental health social workers, who worked closely with the specialist psychiatric team and who received supportive supervision from their professional managers, maintained stable case-loads, but the primary-care attached community psychiatric nurses, who were isolated from the specialist psychiatric team, and who received little supportive supervision from their professional managers, carried case-loads of increasing size. Failure to improve the way in which services for the mentally ill in the community are co-ordinated is likely to perpetuate the worst characteristics of life in the old back wards into the era of ‘community care’.