Dataset Information

Secondary metabolite gene expression and interplay of bacterial functions in a tropical freshwater cyanobacterial bloom.

ABSTRACT: Cyanobacterial harmful algal blooms (cyanoHABs) appear to be increasing in frequency on a global scale. The Cyanobacteria in blooms can produce toxic secondary metabolites that make freshwater dangerous for drinking and recreation. To characterize microbial activities in a cyanoHAB, transcripts from a eutrophic freshwater reservoir in Singapore were sequenced for six samples collected over one day-night period. Transcripts from the Cyanobacterium Microcystis dominated all samples and were accompanied by at least 533 genera primarily from the Cyanobacteria, Proteobacteria, Bacteroidetes and Actinobacteria. Within the Microcystis population, abundant transcripts were from genes for buoyancy, photosynthesis and synthesis of the toxin microviridin, suggesting that these are necessary for competitive dominance in the Reservoir. During the day, Microcystis transcripts were enriched in photosynthesis and energy metabolism while at night enriched pathways included DNA replication and repair and toxin biosynthesis. Microcystis was the dominant source of transcripts from polyketide and non-ribosomal peptide synthase (PKS and NRPS, respectively) gene clusters. Unexpectedly, expression of all PKS/NRPS gene clusters, including for the toxins microcystin and aeruginosin, occurred throughout the day-night cycle. The most highly expressed PKS/NRPS gene cluster from Microcystis is not associated with any known product. The four most abundant phyla in the reservoir were enriched in different functions, including photosynthesis (Cyanobacteria), breakdown of complex organic molecules (Proteobacteria), glycan metabolism (Bacteroidetes) and breakdown of plant carbohydrates, such as cellobiose (Actinobacteria). These results provide the first estimate of secondary metabolite gene expression, functional partitioning and functional interplay in a freshwater cyanoHAB.

SUBMITTER: Penn K

PROVIDER: S-EPMC4139720 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Secondary metabolite gene expression and interplay of bacterial functions in a tropical freshwater cyanobacterial bloom.

Penn Kevin K Wang Jia J Fernando Samodha C SC Thompson Janelle R JR

The ISME journal 20140320 9

Cyanobacterial harmful algal blooms (cyanoHABs) appear to be increasing in frequency on a global scale. The Cyanobacteria in blooms can produce toxic secondary metabolites that make freshwater dangerous for drinking and recreation. To characterize microbial activities in a cyanoHAB, transcripts from a eutrophic freshwater reservoir in Singapore were sequenced for six samples collected over one day-night period. Transcripts from the Cyanobacterium Microcystis dominated all samples and were accomp ...[more]

PMID: 24646695

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Project description:Toxic blooms of cyanobacteria, which can produce cyanotoxins, are prevalent in freshwater, especially in South Korea. Exposure to cyanotoxins via ingestion, inhalation, and dermal contact may cause severe diseases. Particularly, toxic cyanobacteria and their cyanotoxins can be aerosolized by a bubble-bursting process associated with a wind-driven wave mechanism. A fundamental question remains regarding the aerosolization of toxic cyanobacteria and cyanotoxins emitted from freshwater bodies during bloom seasons. To evaluate the potential health risk of the aerosolization of toxic cyanobacteria and cyanotoxins, the objectives of this study were as follows: 1) to quantify levels of microcystin in the water and air samples, and 2) to monitor microbial communities, including toxic cyanobacteria in the water and air samples. Water samples were collected from five sites in the Nakdong River, South Korea, from August to September 2022. Air samples were collected using an air pump with a mixed cellulose ester membrane filter. Concentrations of total microcystins were measured using enzyme-linked immunosorbent assay. Shotgun metagenomic sequencing was used to investigate microbial communities, including toxic cyanobacteria. Mean concentrations of microcystins were 960 μg/L ranging from 0.73 to 5,337 μg/L in the water samples and 2.48 ng/m3 ranging from 0.1 to 6.8 ng/m3 in the air samples. In addition, in both the water and air samples, predominant bacteria were Microcystis (PCC7914), which has a microcystin-producing gene, and Cyanobium. Particularly, abundance of Microcystis (PCC7914) comprised more than 1.5% of all bacteria in the air samples. This study demonstrates microbial communities with genes related with microcystin synthesis, antibiotic resistance gene, and virulence factors in aerosols generated from cyanobacterial bloom-affected freshwater body. In summary, aerosolization of toxic cyanobacteria and cyanotoxins is a critical concern as an emerging exposure route for potential risk to environmental and human health.

Project description:The current study reports the community succession of different toxin and non-toxin producing cyanobacteria at different stages of cyanobacterial harmful algal blooms (CyanoHABs) and their connectivity with nitrogen and phosphorus cycles in a freshwater lake using an ecogenomics framework. Comprehensive high throughput DNA sequencing, water quality parameter measurements, and functional gene expressions over temporal and spatial scales were employed. Among the cyanobacterial community, the lake was initially dominated by Cyanobium during the months of May, June, and early July, and later primarily by Aphanizomenon and Dolichospermum depicting functional redundancy. Finally, Planktothrix appeared in late August and then the dominance switched to Planktothrix in September. Microcystis aeruginosa and Microcystis panniformis; two species responsible for cyanotoxin production, were also present in August and September, but in significantly smaller relative abundance. MC-LR (0.06-1.32 µg/L) and MC-RR (0.01-0.26 µg/L) were two major types of cyanotoxins detected. The presence of MC-LR and MC-RR were significantly correlated with the Microcystis-related genes (16SMic/mcyA/mcyG) and their expressions (r = 0.33 to 0.8, p < 0.05). The metabolic analyses further linked the presence of different cyanobacterial groups with distinct functions. The nitrogen metabolisms detected a relatively higher abundance of nitrite/nitrate reductase in early summer, indicating significant denitrification activity and the activation of N-fixation in the blooms dominated by Aphanizomenon/Dolichospermum (community richness) during nutrient-limited conditions. The phosphorus and carbohydrate metabolisms detected a trend to initiate a nutrient starvation alert and store nutrients from early summer, while utilizing the stored polyphosphate and carbohydrate (PPX and F6PPK) during the extreme ortho-P scarcity period, mostly in August or September. Specifically, the abundance of Aphanizomenon and Dolichospermum was positively correlated with the nitrogen-fixing nif gene and (p < 0.001) and the PPX enzyme for the stored polyphosphate utilization (r = 0.77, p < 0.001). Interestingly, the lake experienced a longer N-fixing period (2-3 months) before non-fixing cyanobacteria (Planktothrix) dominated the entire lake in late summer. The Provo Bay site, which is known to be nutrient-rich historically, had early episodes of filamentous cyanobacteria blooms compared to the rest of the lake.

Dataset Information

Secondary metabolite gene expression and interplay of bacterial functions in a tropical freshwater cyanobacterial bloom.

Publications

Secondary metabolite gene expression and interplay of bacterial functions in a tropical freshwater cyanobacterial bloom.

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