Microbes influencing the Ecosystem around them.

Algae-microbe interactions are a new expanding field of scientific enquiry with an increasing understanding of what the interactions are at the forefront of current research.

Many clades of bacteria have the metabolic pathways to synthesise vitamin B₁₂ whereas algae do not, relying on the Vitamin B₁₂ from other sources.

Vitamins play an important role as cofactors in enzyme action. They are micronutrients, present in very small concentration across the globe and synthesised by many different species of bacteria. Cobalamin (Vitamin B₁₂ ) is a cofactor of the B12-dependent Methionine synthase (METH) which is an enzyme involved in producing the amino acid Methionine. Some species of algae depend on an external source of Vitamin B₁₂ to produce Methionine, other species of algae use another enzyme METE which does not require vitamin B₁₂ to produce Methionine an important amino acid in protein production. However, without cobalamin, this pathway is less efficient.

Some species of Algae such as the green microalgae Chlamydomous reinhardtii have the capacity to express both forms of the methionine pathway. In the presence of Vitamin B₁₂ in the environment the METE gene is repressed in both laboratory (Helliwell et al 2011) and environmental studies. The METH pathway is utilised for Methionine production in this case. Long-term exposure to cobalamin from vitamin B12 producing bacteria in the environment may lead to a loss of the METE Gene in algal lineages.

The present study aimed to understand the changes in metabolism in relation to the presence of Vitamin B₁₂ producing bacteria and algae grown axenically. The green algae Lobomonas rostrata (closely related to C. reinhardtii) was grown under two different treatments, with the Vitamin B₁₂ producing rhizobia bacteria Mesorhizobium loti which exchanges cobalamin for fixed carbon from Photosynthesis. 

In the second treatment, L. rostrata was grown axenically with the addition of supplemented Vitamin B₁₂.

Proteome analysis was undertaken using a database of peptides that can be matched to experimental mass spectra. Chlamydomonas reinhardtii Proteome (a close relative of Lobomonas rostrata) served as a viable match to compare the proteins against in mass spectrometry.

Isobaric tag for relative and absolute quantitation (ITAQ) is a method used to quantify and determine the different sources of proteins in a single experiment. It uses various chemicals of identical mass which are attached to peptides and uses mass spectrometry to determine the source. Allowing you to see how much protein is being translated from the gene sequence. 

The method revealed a reduction in photosynthesis proteins, amino acid metabolism being produced in co-culture compared to axenic culture with B₁₂ supplements. Indicating that the M. loti only produce enough Vitamin B₁₂ for the algae to survive.

Using this approach of metaproteomics in a laboratory model experiment allows you to take a detailed look at processes of interaction between communities.

References:

Helliwell, K. E., Wheeler, G. L., Leptos, K. C., Goldstein, R. E., & Smith, A. G. (2011). Insights into the evolution of vitamin B12 auxotrophy from sequenced algal genomes. Molecular biology and evolution, 28(10), 2921-2933.

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Article Reviewed:

Helliwell, K. E., Pandhal, J., Cooper, M. B., Longworth, J., Kudahl, U. J., Russo, D. A., ... & Wright, P. C. (2018). Quantitative proteomics of a B12‐dependent alga grown in coculture with bacteria reveals metabolic tradeoffs required for mutualism. New Phytologist, 217(2), 599-612.