Size-dependent growth of Microcystis colonies in a shallow, hypertrophic lake: use of the RNA-to-total organic carbon ratio

Abstract

Microcystis was cultured under standard conditions in BG-11 and M-11 media. Using results of an analysis of RNA and total organic carbon (TOC) content, a significant logarithmic relationship between Microcystis growth rate and the RNA/TOC ratio was described to measure the growth rate. Colonial Microcystis samples collected in a shallow, hypertrophic lake (Lake Taihu, China) during May to November 2012 were divided into six size classes (<75, 75-100, 100-150, 150-300, 300-500, and >500 μm), and the RNA/TOC ratio of each class was analyzed to evaluate differences in growth. The growth rate of colonies in the 150-300 μm size class was highest from May to August, but the growth rate increased along with the increase in colony size from September to November. Our results also indicated that water temperature did not change the relationship between growth rate and colony size, but the growth rate of larger colonies was higher than the growth rate of smaller colonies at conditions of low total nitrogen, low total dissolved phosphorus concentration, and high light intensity. Taken together, these results suggest that large colonial Microcystis possess an advantage that is a consequence of this faster growth at lower nutrient concentrations and high light intensities.

Colony formation in the cyanobacterium Microcystis

“…Li et al . () compared the growth rate of colonies sampled from Lake Taihu at different seasons and recorded faster growth rates of larger colonies than smaller colonies under low levels of nitrogen and phosphorus, and at high light intensity, emphasising the competitive ability of colonies under nutrient‐deficient conditions.…”

“…Negative effects of colony size on growth rate have been recorded in the laboratory (Yamamoto & Shiah, ). In field investigations, growth rate has been shown to be negatively correlated with increasing colony size, for colonies greater than 150 µm (Li et al, ; Wilson, Wilson & Hay, ), especially in conditions of low total nitrogen, low total dissolved phosphorus concentration, and high light intensity (Li et al, ). Yamamoto & Shiah () proposed that when colonies are small (< 200 µm), inner‐colony cells grow faster than the peripheral cells and as the colonies become larger, the growth of inner‐colony cells is inhibited by greater self‐shading.…”

Vertical distribution of Microcystis colony size in Lake Taihu: Its role in algal blooms

“…Microcystis blooms occurred during our investigation in summer and autumn when the light intensity was high (although light intensity was not measured in 2011, instantaneous light intensity was recorded as 400 to 1000 μmol•photons/(m 2 •s) during the same sampling process in 2012; Li et al, 2014). Moreover, most colonies collected at different depths were floating at the water surface in the bottles when they were taken back to the laboratory.…”

Evolution of reproductive strategies in incipient multicellularity

“…Size could have positive, negative or neutral effects on growth at each cell increment. The model assumption is corresponding to studies concerning size effect on growth (Yamamoto and Shiah, 2010;Nielsen, 2006;Li et al, 2014;Wilson et al, 2006;Li and Gao, 2004;Wilson et al, 2010). The form of size perturbations used in our work covers a wide range of size functional forms, including those investigated previously (Pichugin et al, 2017.…”

“…Organism size can also affect reproductive strategies as early as nascent multicellularity (Michod, 2007;Solari et al, 2013;Ratcliff et al, 2012;Libby et al, 2014). Field observations are ambiguous about the effects of organism size (Yamamoto and Shiah, 2010;Nielsen, 2006;Li et al, 2014;Wilson et al, 2006;Li and Gao, 2004;Wilson et al, 2010). Here, we consider a broad scope of size effects that can increase, decrease or not change the growth of heterogeneous organisms.…”