Indirect and direct effects of salinity on the quantity and quality of total amino acids in Ulva ohnoi (Chlorophyta)

Abstract

Salinity can affect the quantity and quality of total amino acids (TAAs) in seaweeds indirectly by altering growth rates and thereby diluting or concentrating the amino acid content of the biomass, or directly by altering the synthesis of specific amino acids and osmolytes. This study attempted to partition the indirect and direct effects of salinity on the quantity and quality of TAAs in the green seaweed Ulva ohnoi by culturing it under a range of salinities without nutrient limitation. Both the quantity and quality of TAAs varied across the salinity treatments. Quantity was most strongly related to the growth rate of the seaweed and was highest in the slowest growing seaweed. In contrast, the quality of TAAs (individual amino acids as a proportion of total content) was most strongly related to salinity for all amino acids, although this varied substantially among individual amino acids. Increases in salinity were positively correlated with the proportion of proline (46% increase), tyrosine (36% increase), and histidine (26% increase), whereas there was a negative correlation with alanine (29% decrease). The proportion of methionine, with strong links to the synthesis of the osmolyte dimethylsulfoniopropionate, did not correlate linearly with salinity and instead was moderately higher at the optimal salinities for growth. These results show that salinity simultaneously affects the quantity and quality of TAAs in seaweed through both indirect and direct mechanisms, with growth rates playing the overarching role in determining the quantity of TAAs.

The effect of salinity on the biomass productivity, protein and lipid composition of a freshwater macroalga

“…A reduction in growth and biomass productivity under salinity stress is most likely due to a redirection of available energy towards processes such as osmoregulation rather than cell growth and photosynthesis [2,8,25,48]. Photosynthesis, growth and survival of macroalgae are typically highest at those salinities that the algae are predominantly exposed to in their natural environment [25].…”

“…In addition to affecting the total quantity of protein in the biomass, salinity can also affect the quality of protein (i.e. amino acid composition) [2,30]. More in depth analysis of the quality of protein in Oedogonium biomass cultivated under increased salinity will be necessary, however, to date the composition of amino acids in Oedogonium appears to be relatively hard-wired across environmental conditions, particularly the key essential amino acids of lysine (6.8-7.3% of protein) and methionine (1.6-1.9% of protein) [11].…”

Seaweed as a protein source for mono-gastric livestock

“…Ash contents are comprised of external and internal salts and usually constitute between 20 and 50% of the dry weight (Angell, Mata, de Nys, & Paul, 2015b;McDermid & Stuercke, 2003;McDermid, Stuercke, & Balazs, 2007). Therefore, processing with freshwater has the potential to increase the concentration of protein in seaweeds by an equivalent amount.…”

A comparison of methods for the non-destructive fresh weight determination of filamentous algae for growth rate analysis and dry weight estimation

“…A spinning time of 90 s was adopted for the reticulated spinner. It is recommended that a similar approach is employed when implementing and standardising this method for different algal taxa, varying amounts of algal biomass, or when cultivating in very different conditions, such as extremes of salinity (Angell et al 2015 ).

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“…Variation in the FW/DW ratio is dependent upon the growth conditions. For instance, Angell et al ( 2015 ) found that the FW/DW of Ulva ohnoi was the greatest when cultivated in low to optimal salinities and the lowest when exposed to high salinity. This difference in ratio was most likely caused by a change in osmotic potential.…”