Multicellular behaviour enables cooperation in microbial cell aggregates.

Area of Science:

• Microbial ecology
• Biophysics
• Computational biology

Background:

• Extracellular hydrolysis of biological materials produces oligosaccharides, acting as common goods that promote cooperative microbial growth.
• Cell-cell aggregation can increase resource availability but also create resource gradients, limiting growth within aggregates.

Purpose of the Study:

• To investigate how bacterial behavior influences cooperative growth and resource accessibility within cell aggregates.
• To compare computational model predictions with experimental observations of alginate-degrading *Vibrio splendidus* strains.

Main Methods:

• Development of a computational model to predict cooperation in cell aggregates based on size and resource gradients.
• Experimental analysis of two *Vibrio splendidus* strains with varying alginate lyase secretion capabilities.
• Observation of aggregate formation, internal structure, and growth patterns under different conditions.

Main Results:

• Model predicted restricted cooperation in aggregates >10 µm due to counter gradients.
• Both *Vibrio splendidus* strains formed large aggregates (<50 µm), overcoming diffusion limitations through structural rearrangement.
• Stronger enzyme producers formed aggregates with channels for resource exchange; weaker producers formed dense aggregates with internal cell mixing.

Conclusions:

• Bacterial behaviors, including aggregate structural rearrangement, channel formation, and active swimming, can mitigate resource limitations within aggregates.
• These behaviors facilitate uniform cell growth, demonstrating how microbes overcome competition imposed by resource gradients.