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Toxins 2016, 8(11), 318;

Presence or Absence of mlr Genes and Nutrient Concentrations Co-Determine the Microcystin Biodegradation Efficiency of a Natural Bacterial Community

IMDEA Water Institute, Alcalá de Henares, Madrid 28805, Spain
Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin 12587, Germany
Departamento de Biología, Universidad Autónoma de Madrid, Cantoblanco 28049, Spain
Author to whom correspondence should be addressed.
Academic Editor: Luis Botana
Received: 3 October 2016 / Revised: 26 October 2016 / Accepted: 28 October 2016 / Published: 3 November 2016
(This article belongs to the Collection Marine and Freshwater Toxins)
PDF [1592 KB, uploaded 3 November 2016]


The microcystin biodegradation potential of a natural bacterial community coexisting with a toxic cyanobacterial bloom was investigated in a water reservoir from central Spain. The biodegradation capacity was confirmed in all samples during the bloom and an increase of mlrA gene copies was found with increasing microcystin concentrations. Among the 24 microcystin degrading strains isolated from the bacterial community, only 28% showed presence of mlrA gene, strongly supporting the existence and abundance of alternative microcystin degradation pathways in nature. In vitro degradation assays with both mlr+ and mlr bacterial genotypes (with presence and absence of the complete mlr gene cluster, respectively) were performed with four isolated strains (Sphingopyxis sp. IM-1, IM-2 and IM-3; Paucibacter toxinivorans IM-4) and two bacterial degraders from the culture collection (Sphingosinicella microcystinivorans Y2; Paucibacter toxinivorans 2C20). Differences in microcystin degradation efficiencies between genotypes were found under different total organic carbon and total nitrogen concentrations. While mlr+ strains significantly improved microcystin degradation rates when exposed to other carbon and nitrogen sources, mlr strains showed lower degradation efficiencies. This suggests that the presence of alternative carbon and nitrogen sources possibly competes with microcystins and impairs putative non-mlr microcystin degradation pathways. Considering the abundance of the mlr bacterial population and the increasing frequency of eutrophic conditions in aquatic systems, further research on the diversity of this population and the characterization and conditions affecting non-mlr degradation pathways deserves special attention. View Full-Text
Keywords: microcystin; biodegradation; cyanobacteria; genotype; Sphingopyxis sp.; Paucibacter sp. microcystin; biodegradation; cyanobacteria; genotype; Sphingopyxis sp.; Paucibacter sp.

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Lezcano, M.Á.; Morón-López, J.; Agha, R.; López-Heras, I.; Nozal, L.; Quesada, A.; El-Shehawy, R. Presence or Absence of mlr Genes and Nutrient Concentrations Co-Determine the Microcystin Biodegradation Efficiency of a Natural Bacterial Community. Toxins 2016, 8, 318.

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