EVIDENCE FOR NUTRIENT-DEPENDENT CYANOBACTERIVORY BY THE MIXOTROPHIC CHRYSOPHYTE OCHROMONAS

Mixotrophs occupy a unique position within the microbial food web as primary producers and consumers. The ability to combine two forms of nutrition is theorized to allow mixotrophs to gain prevalence in a variety of aquatic ecosystems, especially when ingestion of particulate prey can supplement nutrient limitation. Ochromonas is a genus of mixotrophic Chrysophyte that includes species spanning the spectrum of mixotrophic strategies, and there is a long history of work dedicated to their variable capacity for phagotrophic ingestion of heterotrophic bacteria. More recently, studies have demonstrated the ability for Ochromonas to ingest potentially toxic cyanobacteria, including Microcystis, a cosmopolitan cyanobacteria with a reputation for forming harmful algal blooms. We used a combination of laboratory experiments in culture and in situ field incubations to investigate cyanobacterivory by Ochromonas with emphasis on the impact of nutrient limitation. Grazing by Ochromonas on toxic Microcystis ranged from 14 cell^-1 day to 31 cell^-1 day, whereas that on the non-toxic strain ranged from 5 cell^-1 day to 19 cell^-1 day. Our results provide evidence that co-culture of Ochromonas with toxic Microcystis with can lead to significant cyanobacterial population decay and microcystin biodegradation under P-limitation. However, in laboratory conditions, N-limitation enhanced grazing by Ochromonas on toxic Microcystis. Collectively, we suggest a role for mixotrophic nanoflagellates as intraguild predators and highlight an unresolved linkage within the microbial food web.

Presentation Preference: Either

Primary Presenter: Sarah Princiotta, Penn State Schuylkill (sbp20@psu.edu)

Authors:

Aloura Gavalis, Penn State Schuylkill  (adg5511@psu.edu)

Ted Harris, Kansas Biological Survey  (ted.daniel.harris@gmail.com)

Dale Holen, Penn State Scranton  (dah13@psu.edu)

Josh Kellogg, Penn State University  (jjk6146@psu.edu)