Composition of Extracellular and Intracellular Polymeric Substances Produced by Scenedesmus and Microcystis

Nitrogen Availability and the Nature of Extracellular Organic Matter of Microalgae

“…Three peaks previously associated with protein were identified: two tryptophan-like peaks, A (λ Ex/Em = 275/320 nm) and B (λ Ex/Em = 290/345 nm), and one tyrosine-like peak, C (λ Ex/Em = 245/330 nm). , These protein-like components are mostly associated with the hydrophobic and high molecular weight (>50 kDa) portions of the EOM; , although small, hydrophilic amino acids (e.g., glutamine and lysine) and peptides can also be present . In addition, two organic acid-like peaks were observed: one fulvic acid-like peak, D (λ Ex/Em = 260–360/450–500 nm), and one humic acid-like peak, E (λ Ex/Em = 330/330–390 nm). ,, In the context of soil chemistry, humic acids are typically between 30 and 50 kDa and tend to become hydrophobic at strongly acidic pH, while fulvic acids have a molecular weight of about 10 kDa and are soluble in all pH conditions .…”

“…In order to analyze the total EOM released by N. salina , Chlorella sp., and H. pluvialis , the concentrations of carbohydrates and proteins in all soluble and bound fractions were summed for each individual species and nutritional condition. Commonly, the dissolved fraction of carbohydrates or the total dissolved carbon (DOC) is considered in isolation, without consideration of the protein fraction . While the DOC should represent the total carbon present in the form of both carbohydrates and proteins, the organic carbon concentration in the microalgal monoculture growth curve can be quite inconsistent due to variations associated with the circadian rhythm of the population .…”

“…One exception to this typical approach is the work by Henderson et al in 2008 on Chlorella vulgaris , Microcystis aeruginosa , Asterionella formosa , and Melorisa sp., where protein and carbohydrate concentrations are presented; however, the extraction method used did not recover any tightly bound material . Previous studies have also shown that proteins and acidic carbohydrates make up the largest portion of the total EOM released by other phytoplankton that are likely to affect industrial processing of cultures. ,, Hydroxy, carboxylic, and fatty acids; free amino acids and peptides; and alkyl alcohols, ketones, and aldehydes have also been identified but in much lower concentrations. ,, Thus, the concentrations of carbohydrates and proteins were measured and taken as surrogates for the EOM released by the microalgae across the nutritional conditions tested. In addition, to interpret the EOM data on a cellular basis, the cell concentration and surface area of the algae samples were determined.…”

“…As above, by accounting for changes in cell concentration and size, the magnitudes and variations in F max can be related to cellular differences in the EOM. This approach has not yet been applied to the study of industrially relevant microalgae that are important in carbon capture and utilization likely because most studies used samples of mixed communities for which the accurate estimation of surface areas is challenging. ,, …”

“…Although extremely useful, the EEM/PARAFAC methodology has been mostly applied to investigate the composition of EOM in mixed planktonic communities and in cyanobacterial cultures that are problematic in water processing . Although microalgae and cyanobacteria belong to different phylogenetic branches, the EOM from cyanobacteria is often referred to as algal EOM. , This can be misleading, as the biochemical composition and structure of the cell membrane (and wall, in the case of microalgae) and the metabolic profiles differ between these two distinct groups of phytoplankton. − Conclusions drawn from samples from the water industry indicate that both the amount and composition of the EOM vary as a function of the growth stage of the microbial community . One objective of a water treatment plant is the removal of microbes and associated harmful metabolites, often requiring full chemical characterization of the EOM to ensure strict quality standards. , In microalgae processing, however, the algal slurry contains some entrapped EOM, and the distinction between the size and hydrophilic/hydrophobic fractions of the EOM are commonly more important than a detailed chemical characterization. − …”