Does the presence of bacteria cause diatoms to photosynthesise faster?

Volatile organic compounds (VOCs) are leaked by autotrophs and constitute 30-40% of DOC in the ocean. In order to understand the ecological dynamics surrounding VOCs, Moore et al. (2019) examined a typical primary producer (Thalassiosira pseudonana) and abundant consumer (Pelagibacter ubique) in mono- and co-culture. They established that most VOCs were reduced in co-culture. Increased cellular ATP in P. ubique growing on VOCs ascertained the cause of the observed decrease. Furthermore, P. ubique grew faster in co-culture, while T. pseudonana did not but had a marginally higher photosynthetic rate. When VOCs were artificially removed from diatom monocultures, the same effect was produced. This led the authors to infer that, through its VOC consumption, P. ubique causes T. pseudonana to photosynthesise faster to make up for diffusive VOC leakage. Instead of increasing its own growth it thus seemingly sustains P. ubique.

Moore et al. (2019) provide some evidence that an abundant bacterium is sustained by a ubiquitous diatom. Nonetheless, they seem to ignore that there is no statistical evidence in favour of their main conclusion; namely that the diatom actually photosynthesises faster in co-culture! This experiment would need to be repeated with a larger sample size to formulate a defendable theory.

Moore, E. R., Davie‐Martin, C. L., Giovannoni, S. J., & Halsey, K. H. (2019). Pelagibacter metabolism of diatom‐derived volatile organic compounds imposes an energetic tax on photosynthetic carbon fixation. Environmental Microbiology, 0(0), 0-0.