Parallelisable non-invasive biomass, fitness and growth measurement of macroalgae and other protists with nephelometry

Abstract

With the exponential development of algal aquaculture and blue biotechnology, there is a strong demand for simple, inexpensive, high-throughput, quantitative phenotyping assays to measure the biomass, growth and fertility of algae and other marine protists. Here, we validate nephelometry, a method that relies on measuring the scattering of light by particles in suspension, as a non-invasive tool to measure in real-time the biomass of aquatic microorganisms , such as microalgae, filamentous algae, as well as non-photosynthetic protists. Nephelometry is equally applicable to optic density and chlorophyll fluorescence measurements for the quantification of some microalgae, but outperforms other spectroscopy methods to quantify the biomass of biofilm-forming and filamentous algae, highly pigmented species and non-photosynthetic eukaryotes. Thanks to its insensitivity to the sample's pigmentation, nephelometry is also the method of choice when chlorophyll content varies between samples or time points, for example due to abiotic stress or pathogen infection. As examples, we illustrate how nephelometry can be combined with fluorometry or image analysis to monitor the quantity and time-course of spore release in fertile kelps or the progression of symptoms in diseased algal cultures.

Real-Time Monitoring of Microalgal Biomass in Pilot-Scale Photobioreactors Using Nephelometry

“…A positive relationship between turbidity and dry weight emerged for all three microalgae (Figure 3ac), showing that nephelometric turbidity can be used as a proxy for biomass density. This result is in line with earlier studies that demonstrate the potential of nephelometry to estimate algal biomass on lab-scale [7,8,20] and is corroborated by our observation that turbidity is positively related with optical density (720 nm) for all three species (Figure 4a-c We considered a broad biomass density range relevant for microalgae culturing in photobioreactors because the dependency of turbidity on biomass density may vary in the same culture over time [8]. Our results confirm this by showing a relatively strong (R² = 0.87-0.93) and nonlinear relationship between turbidity and dry weight for all three species.…”

“…Tight control of microalgal productivity in photobioreactors hinges on a fast, noninvasive and reliable monitoring method to quantify biomass density [5,6]. Over the years, various methods have been used that rely on optical density (spectrophotometry) and chlorophyll fluorescence (fluorometry) as a proxy for biomass [7,8]. However, these methods are inherently confounded by variation in pigment content [7], and do not easily allow for real-time data collection [8].…”

“…Over the years, various methods have been used that rely on optical density (spectrophotometry) and chlorophyll fluorescence (fluorometry) as a proxy for biomass [7,8]. However, these methods are inherently confounded by variation in pigment content [7], and do not easily allow for real-time data collection [8]. Likewise, traditional cell counts or dry weight measurements to more directly quantify microalgal biomass are generally labor-and timeintensive [8,9].…”

“…Nephelometers measure light scatter by suspended particles and are commonly used in various applications including in ecology to assess water turbidity [11], and in medicine and veterinary science to determine the level of proteins in biofluids [12]. This technique was introduced already several decades ago to also quantify algal biomass [13,14] but was never widely implemented due to the low sensitivity, reliability and automatability of the available instruments at the time [7]. Nowadays, these limitations are overcome by several technological improvements, and nephelometry was recently validated on lab-scale to monitor in real time the biomass of aquatic organisms including filamentous fungi [15], macroalgae and microalgae [7].…”

“…This technique was introduced already several decades ago to also quantify algal biomass [13,14] but was never widely implemented due to the low sensitivity, reliability and automatability of the available instruments at the time [7]. Nowadays, these limitations are overcome by several technological improvements, and nephelometry was recently validated on lab-scale to monitor in real time the biomass of aquatic organisms including filamentous fungi [15], macroalgae and microalgae [7]. Consequently, the interest to use nephelometers in larger-scale microalgae photobioreactors is now rapidly increasing.…”