Bacteria are single-celled organisms that must absorb their nutrients by simple diffusion. The dimensions of Thiomargarita namibiensis are several hundred times larger than those of most bacteria, much too large for simple diffusion to operate. How does the bacterium solve this problem?

They have a vacuole inside, that stored the nitrate needed to oxidize sulfide and obtain energy.

Explanation:

Thiomargarita namibiensis is the largest prokaryotic bacterium yet known, it has a spherical shape and reaches up to a size of 0.75 mm wide, which makes it visible to the human eye. It was discovered on the shores of Namibia and It is known as "Sulfur Pearl of Namibia," due to the sulfur granules they store inside and the brightness they produce. The problem with its large dimensions is the larger the surface of the bacteria, the lower the level of nutrient absorption. therefore this bacterium had to develop other mechanisms of nutrient and energy uptake

The survival mechanism of this bacterium is quite particular, first of all, it is an anaerobic bacterium, so it is found in sulfide-rich sediments. Its main feature is a liquid container inside called vacuole, which occupies 98% of its volume. In this vacuole, the nitrate that the bacteria use to oxidize sulfide is stored and thus obtain energy. T. namibiensis is unable to move, so they have to wait until the sea currents transport nitrate-rich seawater to store it in their vacuoles, so they can survive for up to 3 months without any other external substrate.