Isolation and characterisation of monoclonal picocyanobacterial strains from contrasting New Zealand lakes

ABSTRACT

Freshwater picocyanobacteria form the base of microbial food webs in many lakes worldwide but have received less attention than other phytoplankton. Little is known about their potential response to environmental changes such as increased nutrient loading and climate change, due partly to the lack of available cultured and sequenced strains. Here, we isolated 25 monoclonal picocyanobacterial strains from 6 New Zealand lakes with contrasting trophic states. The use of MLA medium instead of BG11 proved highly successful for the rapid isolation of picocyanobacteria. Strains were characterised by sequencing of the 16S ribosomal RNA gene, spectrophotometry, and high-performance liquid chromatography. 16S rRNA gene analysis placed most strains within the cluster 5 picocyanobacterial lineage (sub-cluster 5.2, family: Synechococcaceae). Phylogenetic analysis showed that 12 isolates from Lakes Wakatipu, Hayes, Johnson, and Ellesmere/Te Waihora clustered with strains from a range of Northern Hemisphere locations, suggesting global dispersal of these strains. Pigment characterisation revealed that pink and brown cultures from oligotrophic and some eutrophic lakes were rich in phycoerythrin, while green cultures from eutrophic and hypertrophic lakes were rich in phycocyanin. This diverse group of freshwater cluster 5 picocyanobacterial cultures will provide a new resource to study how these critically important microbes function and respond to changing environmental stressors.

KEYWORDS:

• 16S ribosomal RNA gene
• cluster 5 picocyanobacteria
• MLA medium
• phycocyanin
• phycoerythrin

Acknowledgements

The authors thank Nicky McHugh (University of Otago) for laboratory assistance and culture troubleshooting discussions, Veronica Beuzenberg (Cawthron), Kylie Price, and Alfonso Schmidt (Malaghan Institute) for assistance with the flow cytometry. Nathan Manning (Otago Regional Council) and Dr. Tina Bayer (Environment Canterbury) are acknowledged for their help with sample collection.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

Sequences of the picocyanobacterial isolates have been deposited in Genbank under accession numbers: MZ648797 - MZ648821.

Additional information

Funding

This research was funded by the New Zealand Ministry of Business, Innovation and Employment research programmes; Enhancing the health and resilience of New Zealand lakes (Grant number: UOWX1503) and Our lakes’ health: past, present, future (Grant number: C05X1707). LS thanks the University of Otago for a PhD scholarship. PJC-Y was supported by an APOSTD/2019/009 Post-Doctoral Fellowship from Generalitat Valenciana.