Physiological and biotechnological studies on the microalga Dunaliella, the bacterium Halomonas, and the cyanobacteria Arthrospira and Spirulina.

A bacterial isolate and a microalga were identified to the genus level using 16S and 18S rRNA gene sequences respectively and· phylogenetic trees were constructed. The bacterial isolate belonged to the genus Halomonas and it was called Halomonas sp. NAH1, whereas the microalga was confirmed as belonging to the species Dunalie/la salina GGAP 19/30 which was the source of 18S rRNA gene. Glycerol production by three strains of the unicellular microalga Dunalie/la (D. parva 19/9, D. parva 19/10, and D. salina 19/30) was explored. The strains were grown in batch cultures in a range of salinities (0.1 4.0 M NaCI). Both intracellular and extracellular glycerol concentrations were measured. All three strains grew well over the range of salinities with optimum growth for all strains at 0.1 to 0.4 M NaC1. All strains leak significant amounts of glycerol in batch cultures. Significant leakage of glycerol into the growth medium was found to be an intrinsic property of the three strains tested. Two strains of Dunalie/la salina (GGAP 19/18 and 19/30) were grown in batch cultures and aerated with different concentrations of G02. Strain 19/18 accumulated large amounts of ~-carotene under nitrogen limitation whereas the strain 19/30 did not. Halomonas sp. NAH1 grew optimally at 1.0 M NaCI and utilised glucose, glycerol or betaine as the sole source of carbon. Glucose supported the most rapid growth rate. Sensitivity of NAH1 to antibiotics was determined and tetracycline had the most inhibitory effect on growth. The cyanobacteria Arthrospira fusiformis GGAP 1475/8 and Spirulina platensis UTEX LB 2340 were shown to be only slightly halotolerant with optimum growth for S. platensis at 0.1 M NaC1 and for A. fusiformis at 0.5 M NaC1. Phycobiliprotein content was very low in both strains, but very high protein content (92.9% of the dry weight biomass) was obtained for S. platensis. This strain looks very promising for mass cultivation for food and/or feed purposes. Glucosyl-glycerol was found to be the compatible solute in both A. fusiformis and S. platensis.