Lindavia intermedia (Bacillariophyceae) and Nuisance lake Snow in New Zealand: Chitin Content and Quantitative PCR Methods to Estimate Cell Concentrations and Expression of Chitin Synthase¹

Abstract

Lake snow, caused by the freshwater centric diatom Lindavia intermedia, has become problematic in several large, oligotrophic New Zealand lakes over the past decade. Macroaggregates produced by L. intermedia foul fishing lines, intake screens, and water filters, and have a negative impact on recreational values. It was confirmed that the fibers constituting lake snow are composed of chitin, two chitin synthase genes (chs1 and 2) from L. intermedia were characterized, new qPCR-based tools to quantify the abundance of the species and measure expression of chs2 relative to the reference gene act1 (the product of which has cytoskeletal functions) were developed. The strong heterogeneity and mucilaginous nature of lake snow samples create particular difficulties for calibrations of gene or transcript copy numbers with cell densities and obtaining high yields of mRNA. However, data collected from four lakes during November 2018 and February and May 2019 show that abundance of L. intermedia is always high when lake snow is also abundant, but that a full range of L. intermedia abundance can occur when lake snow is absent, suggesting that chitin production is not obligate in L. intermedia. This result is consistent with the available data for chs2 expression, which suggest higher transcription when lake snow is abundant. Lake snow production by L. intermedia therefore requires an as yet undetermined stimulus independent of cell abundance.

Anthropogenic climate change has altered lake state in the Sierra Nevada (California, USA)

“…Lindavia intermedia and L. costei are most commonly found in oligotrophic to mesotrophic lakes with alkaline water (Berthon et al, 2014; Houk, 2010; Novis et al, 2020; Saros & Anderson, 2015). L. ocellata , which is probably ecologically most similar to the species we observed ( L .…”

Lake snow caused by the invasive diatom Lindavia intermedia can be discriminated from different sites and from other algae using vibrational spectroscopy

“…This is consistent with studies of diatoms and their pigments and exudates. [ 4,21 ] Features that may be associated with lipids were observed in the Raman spectra; bands ranging from 3000 to 2800 cm −1 were observed in the L. intermedia samples but not in Didymosphenia . It is known that lipid content varies with species, geographical location, season, nutrient content and growth phase.…”

“…The geographical positions of the sample collection sites are presented in Table S1. Fresh samples from Lake Wānaka were also collected from three different depths (0–30, 30–60 and 60–90 m) by snow tow [ 4 ] and stored at −20°C prior to analysis. These depth intervals were measured in relation to the length of line towed behind the boat, and therefore, they overestimate the actual depths sampled to some extent.…”

“…Based on the separation in PC scores space and the associated loadings, it appears that the differences observed between the lakes are associated with higher pigment signals in the Lake H awea and Lake Wakatipu samples compared with the Lake W anaka sample with higher relative carotenoid pigments and lipids. Carotenoids would not be present in the lake snow fibres, [4] so these will likely be related to carotenoid content of the L. intermedia cells. [22,31] The same analysis for the IR data is presented in Figure 4.…”

“…[2] Enumeration of L. intermedia is straightforward according to standard microscopic methods and is amenabl to qPCR methodology. [4] However, quantification of its problematic EPS is more difficult. Methods to discriminate the EPS produced by L. intermedia from similar material from other species are particularly needed.…”