Microcystin aids in cold temperature acclimation: Differences between a toxic Microcystis wildtype and non-toxic...

Area of Science:

• Environmental microbiology
• Cyanobacterial physiology
• Toxicology

Background:

• Microcystis aeruginosa produces microcystin, a potent toxin.
• Cold temperatures increase microcystin quotas in M. aeruginosa.
• The fitness advantage of microcystin production at lower temperatures is not fully understood.

Purpose of the Study:

• To investigate if increased microcystin production at colder temperatures provides a fitness advantage to M. aeruginosa PCC 7806.
• To compare the physiological and metabolic responses of a wild-type strain to a non-toxigenic mutant under cold stress.

Main Methods:

• Continuous culture growth of M. aeruginosa PCC 7806 and its non-toxigenic mutant (ΔmcyB) at 26°C and 19°C.
• Assessment of cell concentration, cellular physiology, and reactive oxygen species (ROS) damage.
• Transcriptomic analysis to infer metabolic differences.

Main Results:

• M. aeruginosa PCC 7806 doubled its microcystin quota per cell as temperature decreased from 26°C to 19°C.
• The non-toxigenic mutant exhibited altered photo-physiology at 19°C, including increased electron sinks and non-photochemical quenching.
• The mutant showed increased expression of a glutathione-dependent peroxiredoxin, indicating ROS defense mechanisms.

Conclusions:

• Microcystin production may confer a selective advantage to M. aeruginosa under cold conditions by aiding in oxidative stress management.
• The wild-type strain's strategy of producing microcystin represents a long-term defense against oxidative stress.
• The mutant's response suggests a shorter-term, proactive strategy for dissipating or degrading oxidative stress agents in the absence of microcystin.