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.