Scientists have recently found that an archaebacteria belonging to the phylum Lokiarchaeota can be grown only in co-culture along with a Methanobacterium and another aerobic proteobacterium. The archaeon catabolizes amino acids that are secreted out from the Methanobacterium, producing formate. The formate released from the archaeon is utilized by the Methanobacterium as an energy source. The proteobacterium, by scavenging the oxygen in the environment, provides an anaerobic environment for the archaeon. This interaction between the archaea and bacteria could have resulted in the evolution of present-day eukaryotic cell. The interactions between Lokiarchaeon with Methanobacterium and Lokiarcheon/Methanobacterium with proteobacterium, respectively, can be described as:

• Correct answer
  A

  Mutualism and commensalism
• B

  Mutualism and parasitism
• C

  Commensalism and mutualism
• D

  Mutualism and amensalism

Hence, the correct answer is option: 'A'.