Proteomic Analysis of Unicellular Cyanobacterium Crocosphaera subtropica ATCC 51142 under Extended Light or Dark Growth

The daily light–dark cycle is a recurrent and
predictable
environmental phenomenon to which many organisms, including cyanobacteria,
have evolved to adapt. Understanding how cyanobacteria alter their
metabolic attributes in response to subjective light or dark growth
may provide key features for developing strains with improved photosynthetic
efficiency and applications in enhanced carbon sequestration and renewable
energy. Here, we undertook a label-free proteomic approach to investigate
the effect of extended light (LL) or extended dark (DD) conditions
on the unicellular cyanobacterium Crocosphaera subtropica ATCC 51142. We quantified 2287 proteins, of which 603 proteins,
were significantly different between the two growth conditions. These
proteins represent several biological processes, including photosynthetic
electron transport, carbon fixation, stress responses, translation,
and protein degradation. One significant observation is the regulation
of over two dozen proteases, including ATP-dependent Clp-proteases
(endopeptidases) and metalloproteases, the majority of which were
upregulated in LL compared to DD. This suggests that proteases play
a crucial role in the regulation and maintenance of photosynthesis,
especially the PSI and PSII components. The higher protease activity
in LL indicates a need for more frequent degradation and repair of
certain photosynthetic components, highlighting the dynamic nature
of protein turnover and quality control mechanisms in response to
prolonged light exposure. The results enhance our understanding of
how Crocosphaera subtropica ATCC 51142
adjusts its molecular machinery in response to extended light or dark
growth conditions.