Endosymbiosis before eukaryotes: mitochondrial establishment in protoeukaryotes

Area of Science:

• Microbiology
• Evolutionary Biology
• Cell Biology

Background:

• Endosymbiosis and organellogenesis are rare in prokaryotes, with mitochondria as the primary example.
• Prokaryotic symbiosis is common, yet other endosymbiotic events remain largely undiscovered.
• The initial interaction and internalization mechanisms for endosymbionts are not fully understood.

Purpose of the Study:

• To explore mechanisms driving unicellular microbial symbiosis evolution, focusing on prokaryote-prokaryote interactions.
• To investigate the evolutionary stability of inter-species microbial interactions.
• To identify challenges in the evolution of stable eukaryotic lineages from endosymbiosis, particularly concerning mitochondria.

Main Methods:

• Review of existing literature on microbial symbiosis and endosymbiosis.
• Analysis of ecological and evolutionary factors influencing symbiotic stability (dependence, proximity, cost-benefit).
• Exploration of various internalization mechanisms (parasitism, engulfment, phagocytosis).

Main Results:

• Symbioses can evolve from exploitative interactions, not necessarily mutualism.
• Cooperation does not automatically lead to stable mutualism.
• Lack of evidence for mutual syntrophy suggests mitochondria originated from parasitic or phagotrophic interactions.

Conclusions:

• Assumptions about initial mutualism in endosymbiosis are perilous.
• Mitochondrial origin likely involved an exploitative interaction rather than mutual syntrophy.
• Further research is needed to understand the diversity and evolution of prokaryotic endosymbiosis.