Question 15

A symbiotic association between marine microalgae and bacteria of the genus Alteromonas assists the microalgae in the scavenging and uptake of dissolved phosphate from seawater.

A marine biology research team investigated how Alteromonas bacteria affect the growth and phosphorus uptake in microalgae of the species Chlorella.

Wild-type (WT) microalgae have normal, high-density cell-surface phosphate transporters.
Mutant ( $p h o - 1$ ) microalgae have defective, restricted phosphate transporters resulting in a lower phosphate uptake capacity.

Both $p h o - 1$ mutant and wild-type microalgae were cultured in controlled, low-phosphate flasks. Half of the cultures of each strain were inoculated with Alteromonas bacteria, while the other half were left uninoculated. After 14 days, the dry biomass of the culture and the total cellular phosphorus content of the microalgae were measured.

The results are summarised in the table below:

Algal strain	Alteromonas bacterium added	Mean dry biomass ( $L−1\text{mg L}^{-1}$ )	Mean phosphorus content ( $cells)−1\mu\text{g } (10^6 \text{ cells})^{-1}$ )
$p h o - 1$ mutant	No	$14.20 \pm 1.50$	$1.85 \pm 0.15$
$p h o - 1$ mutant	Yes	$22.40 \pm 1.80$	$3.10 \pm 0.25$
Wild type	No	$45.80 \pm 2.40$	$6.40 \pm 0.40$
Wild type	Yes	$40.20 \pm 3.10$	$5.55 \pm 0.50$

The researchers concluded that the addition of the symbiotic bacterium Alteromonas fully compensated for the defective phosphate transporter system in the mutant microalgae.

Evaluate this conclusion using the data provided.