Regulatory and metabolic adaptations in the nitrogen assimilation of marine picocyanobacteria

Abstract

Prochlorococcus and Synechococcus are the two most abundant photosynthetic organisms on Earth, with a strong influence on the biogeochemical carbon and nitrogen cycles. Early reports demonstrated the streamlining of regulatory mechanisms in nitrogen metabolism and the removal of genes not strictly essential. The availability of a large series of genomes, and the utilization of latest generation molecular techniques have allowed elucidating the main mechanisms developed by marine picocyanobacteria to adapt to the environments where they thrive, with a particular interest in the strains inhabiting oligotrophic oceans. Given that nitrogen is often limited in those environments, a series of studies have explored the strategies utilized by Prochlorococcus and Synechococcus to exploit the low concentrations of nitrogen-containing molecules available in large areas of the oceans. These strategies include the reduction in the GC and the cellular protein contents; the utilization of truncated proteins; a reduced average amount of N in the proteome; the development of metabolic mechanisms to perceive and utilize nanomolar nitrate concentrations; and the reduced responsiveness of key molecular regulatory systems such as NtcA to 2-oxoglutarate. These findings are in sharp contrast with the large body of knowledge obtained in freshwater cyanobacteria. We will outline the main discoveries, stressing their relevance to the ecological success of these important microorganisms.

Proteomics analysis reveals differential acclimation of coastal and oceanic Synechococcus to climate warming and iron limitation

“…Further, enzymes related to the amino acid glutamate, an essential molecule for N assimilation and metabolism, were significantly reduced under Fe limitation and its combination with warming ( Supplementary Table S2 ). For example, glutamate synthase, a critical enzyme in the GS-GOGAT pathway, is the key regulatory point that assimilates N to synthesize glutamate ( Muro-Pastor et al, 2005 ; Díez et al, 2023 ). The Fe-S center of this enzyme as well as its reliance on reducing power from ferredoxin and ATP from photosynthesis indicate various reasons for the observed decline in the concentration of glutamate synthase under Fe limitation in the oceanic strain.…”

Taxonomic, Phylogenomic and Bioactivity Profiling of Novel Phycosphere Bacterium from Model Cyanobacterium Synechococcus elongatus PCC 7942

“…Different cyanobacterial components (e.g., pigments, proteins, polysaccharides, and lipids) display varied biological availability during the decomposition process. However, the majority of Synechococcus-derived organic matter is easily labile for use by the heterotrophic bacterial community [5]. Thus, through varied interactions, marine phytoplanktons and their heterotrophic bacterial communities compose a closely related regulator alliance in the oceans by acting as the dominant primary producers (phytoplankton) and biogeochemical cycle drivers (bacteria), respectively [6].…”

A genomic view of environmental and life history controls on microbial nitrogen acquisition strategies

“…For example, assimilating one molecule each of nitrite (NO 2 − ) and nitrate (NO 3 − ) consumes six and eight reducing equivalents, respectively. As a result, even in marine waters with plenty of NO 3 − , many phytoplankton preferably use less abundant forms of N such as ammonium, amino acids and urea (reviewed in Díez et al, 2023 ; Hutchins & Capone, 2022 ). BNF, the process by which microbes assimilate atmospheric N 2 , requires 8 reducing equivalents and 16 ATPs per mole of N 2 fixed.…”