Abstract
During phases of nitrogen starvation, the photosynthetic cyanobacterium Synechocystis sp. PCC 6803 produces polyhydroxybutyrate (PHB). This polymer is of high biotechnological relevance because of its potential as biodegradable plastic. Analysis of the Synechocystis genome revealed an operon (slr0058-slr0061) containing several genes, which are putatively related to the PHB metabolism. While Slr0058 show similarities with the regulatory phasin PhaF, the protein Slr0060 could serve as an intracellular PHB depolymerase. Investigation of respective knock-out mutants showed no distinct phenotype for the strain lacking Slr0060, whereas the Δslr0058 mutant displayed a growth impairment as well as a change in pigmentation. During nitrogen starvation, the Δslr0058 mutant produced in average more than twice the amount of PHB granules per cell, while the overall amount of PHB remained the same. This indicates that Slr0058 plays a role in PHB granule formation and controls it surface-to-volume ratio. GFP-tagged Slr0058 did not co-localize with PHB granules during nitrogen starvation but aggregated in distinct foci during vegetative growth. This work helps to better understand the PHB metabolism of Synechocystis sp. PCC 6803, coming closer to a sustainable, industrial production of PHB.
Highlights
Cyanobacteria are a diverse group of bacteria, which are able to perform oxygenic photosynthesis
By analyzing the Synechocystis genome for putative homologies of phasins, we identified an operon of genes of unknown function, containing members that show similarities to phasins from other organisms
The gene product of slr0060 was recently located in the same subcellular region as other PHB-related proteins, indicating a relevance of Slr0060 for the PHB metabolism (Baers et al, 2019)
Summary
Cyanobacteria are a diverse group of bacteria, which are able to perform oxygenic photosynthesis. Due to their phototrophic lifestyle they are considered as potential hosts for the sustainable production of industrially relevant compounds. Synechocystis is an important strain for basic research, due to its diverse lifestyles, as it supports phototrophic, heterotrophic or mixotrophic growth (Zavrel et al, 2017). The last two are relevant under the conditions of nitrogen starvation. For this condition, Synechocystis has evolved a unique adaptation strategy, namely chlorosis (Collier and Grossman, 1992; Krasikov et al, 2012)
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