Do Microcystis laboratory cultures hold clues to bacterial microcystin degradation?
Start Date
25-5-2022 10:00 AM
End Date
25-5-2022 10:15 AM
Abstract
Microcystins do not accumulate in freshwater ecosystems, and their degradation rates in freshwater suggest that both biotic and abiotic factors play critical roles in their removal. Most Microcystis aeruginosa laboratory cultures harbor a microbiome made up of heterotrophic bacteria that use Microcystis-produced organic matter for growth. We analyzed the microbiome of two M. aeruginosa cultures from Lake Erie with metagenomic sequencing, and found that some of their metagenome-assembled genomes included known genes for microcystin degradation. We tested whether these mixed communities can degrade microcystins by incubating them with Microcystis lysate (freeze-thawed cells) and monitoring dissolved microcystins by liquid chromatography mass spectrometry (LC/MS). We also tested whether these bacterial populations could incorporate carbon and nitrogen from microcystin-LR (MC-LR), the most common and most toxic of the microcystins, as well as bacteria from non-toxic Microcystis culture as a control. To accomplish this, we first labeled a M. aeruginosa culture with 13C and 15N stable isotopes, purified extracted MC-LR from the cell pellets, and added this labeled substrate back to Microcystis-bacteria co-cultures. Using nanoscale imaging mass spectrometry (NanoSIMS), we quantified the net incorporation of 15N and 13C into heterotrophic bacteria as well as the Microcystis cells to identify the fate of MC-LR C and N in this microbial ecosystem.
Do Microcystis laboratory cultures hold clues to bacterial microcystin degradation?
Microcystins do not accumulate in freshwater ecosystems, and their degradation rates in freshwater suggest that both biotic and abiotic factors play critical roles in their removal. Most Microcystis aeruginosa laboratory cultures harbor a microbiome made up of heterotrophic bacteria that use Microcystis-produced organic matter for growth. We analyzed the microbiome of two M. aeruginosa cultures from Lake Erie with metagenomic sequencing, and found that some of their metagenome-assembled genomes included known genes for microcystin degradation. We tested whether these mixed communities can degrade microcystins by incubating them with Microcystis lysate (freeze-thawed cells) and monitoring dissolved microcystins by liquid chromatography mass spectrometry (LC/MS). We also tested whether these bacterial populations could incorporate carbon and nitrogen from microcystin-LR (MC-LR), the most common and most toxic of the microcystins, as well as bacteria from non-toxic Microcystis culture as a control. To accomplish this, we first labeled a M. aeruginosa culture with 13C and 15N stable isotopes, purified extracted MC-LR from the cell pellets, and added this labeled substrate back to Microcystis-bacteria co-cultures. Using nanoscale imaging mass spectrometry (NanoSIMS), we quantified the net incorporation of 15N and 13C into heterotrophic bacteria as well as the Microcystis cells to identify the fate of MC-LR C and N in this microbial ecosystem.