Taxonomic and Genotypical Heterogeneity of Microcystin degrading Bacterioplankton in Western Lake Erie

Anjali Krishnan; Yuqin Zhang; Meaghan Balaban; Youngwoo Seo; Xiaozhen Mou

doi:10.1016/j.hal.2020.101895

Taxonomic and Genotypical Heterogeneity of Microcystin degrading Bacterioplankton in Western Lake Erie

Harmful Algae. 2020 Sep:98:101895. doi: 10.1016/j.hal.2020.101895. Epub 2020 Aug 29.

Authors

Anjali Krishnan¹, Yuqin Zhang², Meaghan Balaban¹, Youngwoo Seo³, Xiaozhen Mou⁴

Affiliations

¹ Biological Science Department, Kent State University, Kent Ohio 44242, U.S.A.
² Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, 1 Tiantan Xi Li, Beiing 100050, China.
³ Department of Civil and Environmental Engineering, University of Toledo, Mail stop 307, 3006 Nitschke Hall, Toledo, OH, 43606, U.S.A.
⁴ Biological Science Department, Kent State University, Kent Ohio 44242, U.S.A.. Electronic address: xmou@kent.edu.

PMID: 33129453
DOI: 10.1016/j.hal.2020.101895

Abstract

Microcystins (MCs) are among the predominant cyanotoxins that are primarily degraded by heterotrophic bacteria in various freshwater environments, including Lake Erie, a Laurentian Great Lake. However, despite the prevalence of MCs in Lake Erie basins, our knowledge about the taxonomic diversity of local MC-degrading bacteria is largely limited. The current study obtained thirty-four MC-degrading bacterial pure isolates from Lake Erie surface water and characterized their taxonomical and phenotypic identities as well as their MC-degradation rates under different pH, temperature, availability of organic substrates and with other MC-degrading isolates. Obtained MC-degrading isolates included both Gram-positive (18 isolates of Actinobacteria and Firmicutes) and Gram-negative bacteria (16 isolates of Gamma-proteobacteria); and 7 of these isolates were motile, and 13 had the capacity to form biofilms. In general, MC-degradation rates of the isolates were impacted by temperature and pH but insensitive to the presence of cyanobacterial exudates. At the optimal temperature (30-35°C) and pH (7-8), individual isolates degraded MC-LR, the most abundant MC isomer, at an average of 0.20 µg/mL/hr. With additions of cyanobacterial exudates, only Pseudomonas sp. LEw-2029, a non-motile biofilm maker, showed increased MC degradation (0.25 µg/mL/hr). Five out of nine tested dual culture mixtures showed rises in MC degradation rates than their corresponding monocultures; the highest rate reached 0.40 µg/mL/hr for the pair LEw-(1132 + 2029). PCR amplification of mlrA genes yielded negative results for all isolates; subsequent enzyme assay-Mass Spectrum analysis identified no product associated with the mlr gene-based MC degradation pathway. Collectively, our results demonstrated that a diversity of indigenous Lake Erie bacteria can degrade MCs via a novel mlr-independent pathway. Obtained MC degraders, especially Pseudomonas sp. LEw-2029, may serve as candidates for the development of biological filters to remove cyanotoxins in water treatment systems.

Keywords: CyanoHAB; Degradation; Lake Erie; MLR-Independent; Microcystins.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Aquatic Organisms
Cyanobacteria*
Lakes
Microcystins*
Temperature

Substances

Microcystins