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Picture Courtesy: PIB

Context:

Freshwater sponges which host diverse microbial communities vital for ecosystem health, have been found to have the potential to act both as bioindicators and absorbents of toxic metals like arsenic, lead, and cadmium and can be a promising solution for bioremediation.

What are Freshwater Sponges?

Freshwater sponges are simple multicellular organisms belonging to the phylum Porifera. They are commonly found attached to rocks, vegetation, or submerged surfaces in lakes, ponds, calm river stretches, and canals.

They are filter feeders, continuously pumping water through their bodies and trapping:

• bacteria
• protozoa
• suspended organic matter

This constant filtration not only helps in feeding but also makes them excellent natural monitors of water quality.

Biology of Sponges:

Freshwater sponges display several unique biological features:

• No true tissues or organs: Their bodies consist of loosely organized cells performing specialized functions.
• Porous body design: The term Porifera literally means pore bearer. Numerous tiny pores allow water to circulate through a network of canals.
• Supporting skeleton of spicules: Their bodies are strengthened by microscopic, needle-shaped spicules, usually made of silica or spongin.
  The structure of these spicules helps in species identification.

Functions of Sponges:

Sponges maintain a continuous flow of water through their bodies:

Water entry: Water enters through small pores called ostia.

Filtration: Specialized cells called choanocytes capture food particles.

Water exit: Cleaned water exits through larger openings called oscula.

A single sponge can filter several litres of water daily, thereby improving the clarity of its environment. 

Relationship between sponges and microbes:

The sponge–microbe relationship is mutualistic:

• Sponges offer shelter, physical protection, and a continuous supply of nutrient-laden water
• Microbes contribute nutrient cycling, chemical defense, and detoxification of pollutants

This cooperation enhances the ability of sponges to survive in contaminated habitats 

Key Findings of the Study:

Effective bioindicators: Freshwater sponges were found to accumulate high concentrations of arsenic, lead, and cadmium, much higher than the surrounding water, making them reliable indicators of metal pollution. 

High bioaccumulation capacity: Sponges function as natural absorbents, storing toxic metals within their tissues—highly relevant for heavy-metal-affected regions of the Gangetic plain.

Distinct microbial communities: Microbes living inside sponges differ significantly from those

present in surrounding water and are influenced by sponge species and habitat characteristics.0 

Metal-adapted microbes: Sponge-associated bacteria possess genes linked to:

• metal ion transport
• resistance to heavy metals
• antimicrobial resistance

These features enable microbes not only to tolerate contamination but also to assist in detoxifying polluted aquatic systems. 

Conclusion:

Sponges, along with their associated microbes, act as natural biofilters that trap, concentrate, and help detoxify heavy metals from water. Their high filtration capacity, ability to bioaccumulate toxic metals, and symbiotic microbial communities make them effective tools for monitoring and mitigating metal pollution, particularly in vulnerable freshwater ecosystems. 

Source: PIB