Characterization of filamentous cyanobacteria and their effect on slow sand filters

Abstract

Safe and clean drinking water delivery is challenged by climate change, as elevated temperatures can promote the growth of pathogens and other detrimental microorganisms. The microbial processes underlying drinking water production in slow sand filters (SSFs) are largely uncharacterized, limiting the possibilities of improving this technology. Periodical clogging, potentially by microbes, disrupts the flow and necessitates the removal of the top sand layer.

This study aimed to identify microbial causes of SSF clogging by relating the differential pressure of all SSFs in a drinking water treatment plant (n=20) to the abundance of specific taxa within the sand biofilm, estimated by 16s rRNA amplicon sequencing and qPCR. Phylum-level microbial signatures of clogged filters were determined using coda4microbiome and glmnet. The models explained 78% and 70% of the variation in head loss, respectively, and identified phylum Cyanobacteria as the most important factor increasing head loss.

Cyanobacteria have been suggested as possible clogging causes in previous studies and may produce taste-and-odor compounds and cyanotoxins. To our knowledge, none have been isolated from SSFs, thus their impact on water quality and filter function is unknown. Cultivation of 3 filamentous cyanobacteria was achieved from SSFs, representing the first whole genome sequences of the poorly defined Anagnostidinema clade.
Supplementation with vitamin B7 (biotin) lead to improved growth. The lack of B7 biosynthetic pathways in our isolates, suggests that cross-feeding occurs in the SSF ecosystem. Further analysis of pathways implicated in drinking water safety and slow sand filter operation is recommended.

Understanding cyanobacterial growth conditions in SSFs is a step towards the definition of their ecological role in these communities. Eventually, community engineering directed toward Cyanobacteria may improve filtration efficacies and operational management of the treatment plants.

Popular Abstract

Cyanobacteria: how do they impact drinking water production?

Society is dependent on the delivery of safe and clean drinking water. For drinking water to be considered safe, it has to be free from pathogens. However, this does not mean that it should be free from all microorganisms, as the microbial community present in it is important in several circumstances.

The drinking water microbial community is extremely diverse across all its stages (from source to distribution) and accumulates in biofilms. Biofilms are complex microbial communities embedded in a viscous and sticky substance that can adhere to surfaces. Biofilters such as slow sand filters (SSFs) are an example of an indispensable biofilm. They are used to improve water quality through a combination of physical and biological mechanisms, as gravity forces the water to slowly pass through a bed of sand. However, the exact functioning of this biological process is not well-known.

Inside the diverse communities of SSFs, this project focused on cyanobacteria. Cyanobacteria are microorganisms able to perform photosynthesis. Ancient cyanobacteria helped make the atmosphere oxygen-rich, and some of them eventually became the chloroplasts of plants. In SSFs, they reside in the top layer, where they receive enough light. They are important in the community as the basis of the food web. However, they can also cause some issues, as they could cause clogging of the filters and/or produce detrimental taste-and-odor compounds and harmful toxins, negatively affecting the quality and safety of the drinking water.

Using a machine learning approach, we showed that the presence of cyanobacteria was linked to clogging of the filters. To help us understand how this can happen, we isolated cyanobacteria from sand in the SSFs in the treatment plant at Ringsjöverket (Stehag, Sweden). For the first time ever, we sequenced the genome of these specific cyanobacteria, called Anagnostidinema, which will help update the cyanobacterial family tree.

As with humans, the isolated cyanobacteria grew better when fed vitamin supplements. Since unlike us, bacteria cannot take vitamin pills, this means that other members of the microbial community must be collaborating with them to provide vitamin in exchange for other compounds in the SSFs.

Increased temperatures caused by climate change can intensify microbial growth, increasing the difficulty of delivering safe and clean drinking water. If we were able to understand how cyanobacteria thrive in SSFs, we could modify their growth conditions to limit filter clogging and improve the functioning of the drinking water treatment plants.

Master’s Degree Project in Molecular Biology, 45 credits, 2024
Department of Biology, Lund University

Advisor: Catherine Paul & Tage Rosenqvist
Division of Applied Microbiology, Department of Chemistry

• author: Feijoo Rey, Iria
• supervisor: Catherine Paul; Tage Rosenqvist
• organization: Degree Projects in Molecular Biology
• course: MOBN02 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9176349
• date added to LUP: 2024-10-09 14:48:09
• date last changed: 2024-10-09 14:48:09