Biology subjects

Mantovani, O.

Publications and source records attributed to Mantovani, O..

3 recordsLinked to original sources

bioRxiv2023

Diurnal rhythm causes metabolic crises in the cyanobacterial mutants of c-di-AMP signalling cascade

In nature, the photoautotrophic lifestyle of cyanobacteria has to cope with the successive diurnal changes in light supply. Light supply throughout the day enables photosynthesis and glycogen biosynthesis, while night phases require the switch to a heterotrophic-like lifestyle relying on glycogen catabolism. We previously highlighted a unique function of the carbon control protein, SbtB, and its effector molecule c-di-AMP, for the nighttime survival of cyanobacteria through the regulation of glycogen anabolism. However, the extent to which c-di-AMP and SbtB impact the cellular metabolism for day-night survivability remained elusive. To gain better understanding of cellular processes regulated by SbtB or c-di-AMP, we compared the metabolomic and proteomic landscapes of {Delta}sbtB and the c-di-AMP-free ({Delta}dacA) mutants of the model strain Synechocystis sp. PCC 6803. While our results indicate that the cellular role of SbtB is restricted to carbon/glycogen metabolism, the diurnal lethality of {Delta}dacA seems to be a sum of dysregulation of multiple metabolic processes. These processes include photosynthesis and redox regulation, which lead to elevated levels of intracellular ROS and glutathione. Further, we show an impact of c-di-AMP on central carbon as well as on nitrogen metabolism. Effects on nitrogen metabolism are linked to reduced levels of the global nitrogen transcription regulator NtcA and highlighted by an imbalance of the glutamine to glutamate ratio as well as reduced metabolite levels of the arginine pathway. We further identified the HCO3- uptake systems, BicA and BCT1 as novel SbtB targets, in agreement with its broader role in regulating carbon homeostasis.

microbiology↗

bioRxiv2023

PII signal transduction superfamily acts as a valve plug to control bicarbonate and ammonia homeostasis among different bacterial phyla

Life on Earth relies on carbon and nitrogen assimilation by RubisCO and GS-GOGAT enzymes, respectively, whose activities depend on a constant supply of inorganic carbon (Ci) and nitrogen (N). Members of the PII signal transduction superfamily are among the most ancient and widespread cell signaling proteins in nature. One of their most highly conserved functions is controlling Ci- and N-transporters, a feature found in different phyla of the Archaea and in both Gram-positive and Gram-negative bacteria. Recently, we identified the PII-like protein SbtB as Ci-sensing module, mainly controlling the HCO3- transporter SbtA in cyanobacteria. Similar to canonical PII proteins, SbtB is able to bind the adenine nucleotides ATP and ADP. Unlike those, it also binds AMP and preferentially binds the second messenger cAMP and c-di-AMP. The functional significance of the binding of different adenyl-nucleotides to SbtB has remained elusive, particularly in the context of the interaction of SbtB with SbtA. By a combination of structural, biochemical and physiological analysis, we revealed that by binding to SbtA, SbtB acts as unidirectional valve, preventing the reverse transport of intracellular enriched bicarbonate. This mechanistic principle holds true for the PII protein from Bacillus acting on the ammonium transporter AmtB, suggesting an evolutionary conserved role for PII superfamily proteins in controlling unidirectional flow of different transporters.

microbiology↗

bioRxiv2019

High density cultivation for efficient sesquiterpenoid biosynthesis in Synechocystis sp. PCC 6803

Cyanobacteria and microalgae are attractive phototrophic host systems for climate-friendly production of fuels and other high-value chemicals. The biosynthesis of an increasing diversity of industrially relevant compounds such as terpenoids has been demonstrated in recent years. To develop economically feasible and sustainable process designs, major challenges still remain regarding intracellular carbon partitioning, specific metabolic pathway activities and efficient cultivation strategies. Here, we present a technical study on comparative characteristics of sesquiterpene and sesquiterpene alcohol accumulation in engineered strains of Synechocystis sp. PCC 6803 (substrain GT-U) under different growth conditions and cell densities. This study particularly focuses on the basic applicability of a commercial High Density Cultivation platform in the presence of a dodecane overlay, which serves as a standard in-situ extractant and sink for various hydrophobic biochemicals. Significantly, the presented data demonstrate high volumetric productivities of (E)--bisabolene under high-density conditions that are more than two orders of magnitude higher than previously reported for cyanobacteria. Operating in a two-step semi-batch mode over a period of eight days, average final volumetric titers of 179.4 {+/-} 20.7 mg * L-1 were detected. Likewise, the sesquiterpene alcohols (-)-patchoulol and (-)--bisabolol accumulated to many times higher levels in high density cultivation than under standard batch conditions, with final titers of 17.3 {+/-} 1.85 mg * L-1 and 96.3 {+/-} 2.2 mg * L-1, respectively. In contrast, specific product accumulation (mg * L-1 * OD750-1) was compromised particularly for bisabolene in the high density system during phases of high biomass accumulation rates. Volumetric productivities were high during linear growth at high densities, distinctly outperforming standard batch systems. While the presented data highlight the benefits of high-density strategies for highly efficient phototrophic terpenoid production, they further point at the presence of major metabolic bottlenecks for engineered terpenoid biosynthesis and the requirement for systematic and/or targeted strategies to sustainably redirect inherent carbon fluxes in cyanobacteria. Together, our data provide additional insights into growth- and density-related effects on the efficiency of product accumulation, introducing low-scale High Density Cultivation as a rapid and efficient platform for screening of heterologous terpenoid production in cyanobacteria.

bioengineering↗