Picocyanobacteria aggregation as a response to predation pressure: direct contact is not necessary

Abstract

Picocyanobacteria (cells <2 µm) can be found either as single-cells (Pcy) or embedded in a mucilaginous sheath as microcolonies or colonies (CPcy). It has been demonstrated that phenotypic plasticity in picocyanobacteria (i.e. the capability of single-cells to aggregate into colonies) can be induced as a response to grazing pressure. The effect of the presence of different predators (cladocerans and rotifers) over the morphological composition of picocyanobacteria were studied in a natural community, and it was observed that the abundance of CPcy significantly increased in all treatments with zooplankton with respect to the Control without zooplankton. The aggregation capability was also evaluated in a single-cell strain, by adding conditioned medium of flagellates, rotifers and cladocerans. The proportion of cells forming colonies was significantly higher in all treatments with conditioned medium regardless the predator. These results suggest that the aggregation of Pcy can be induced as a response of the predation pressure exerted by protists and different zooplankters, and also that Pcy has the capability to aggregate into CPcy even without a direct contact with any predator, most probably due to the presence of an infochemical dissolved into the water that would not come from disrupted Pcy cells.

Ecophysiological analysis reveals distinct environmental preferences in closely related Baltic Sea picocyanobacteria

“…It should also be noted that morphology and morphotypes are not stable forms. For example, single cells can aggregate (or remain attached) and form microcolonies under the presence of heterotrophic bacteria, grazing pressure, or exposure to UV radiation (Callieri et al, 2011; Cruz & Neuer, 2019; Ospina‐Serna et al, 2020).…”

Factors influencing the pigment composition and dynamics of photoautotrophic picoplankton in shallow eutrophic lakes

“…genera Aphanocapsa , Aphanothece , Chroococcus , Coelosphaerium [ 10 , 57 ]. Ospina-Serna et al [ 58 ] demonstrated that the presence of predatory cladocerans and rotifers increases the formation of colonies of individual cells. Although these colonial forms are present in Võrtsjärv, in this study they are only partly represented in PPP since the colony as a unit would not pass through the 2 μm filter.…”

Increases in Picocyanobacteria Abundance in Agriculturally Eutrophic Pampean Lakes Inferred from Historical Records of Secchi Depth and Chlorophyll-a

“…However, the increase in the abundance of tiny cells resembling Pcy over the last decades was apparent while quantifying nano-and micro-phytoplankton under the inverted microscope (I. Izaguirre, personal communication). On the other hand, Pcy cells often aggregate to form microcolonies in response to different stimuli [45,46], and there is typically a positive relationship between the abundance of microcolonies and that of single Pcy cells. Our historical records of microcolonies abundance for a few Pampean lakes from 1987 [47] to 2015 [48,49] show remarkable abundance increases.…”

“…Changes in plankton composition might alter the trophic interactions, and consequently the flow of matter and energy through the food web. For instance, certain species of zooplankton mediate the phenotypic plasticity of Pcy, promoting their aggregation into colonies [44][45][46]. The decrease in the average cell size of phytoplankton would enhance the relative importance of intraguild predators at intermediate trophic levels of the food web, favoring the heterotrophic microbial pathway through small protists with the increase in complexity and consequent reduction in trophic efficiency, as it occurs in large tropical lakes [4].…”