3-Hydroxybutyrate Derived from Poly-3-Hydroxybutyrate Mobilization Alleviates Protein Aggregation in Heat-Stressed Herbaspirillum seropedicae SmR1

Abstract

<jats:p>Under conditions of carbon starvation, thermal-, osmotic- or oxidative-shocks, mutants affected in the synthesis or mobilisation of PHB are known to survive less well. It is still unclear if the synthesis and accumulation of PHB are sufficient to protect bacteria against stress conditions, or if the stored PHB has to be mobilised. Here, we demonstrated that mobilisation of PHB in <jats:italic>Herbaspirillum seropedicae</jats:italic> SmR1 was heat shock activated at 45°C. The <jats:italic>in situ</jats:italic> proton nuclear magnetic resonance spectroscopy (<jats:sup>1</jats:sup>H-NMR) showed that heat shock increased amounts of 3-hydroxybutyrate (3HB) only in <jats:italic>H. seropedicae</jats:italic> strains able to synthesise and mobilise PHB. <jats:italic>H. seropedicae</jats:italic> SmR1 mutants unable to synthesise or mobilise PHB were more susceptible to heat shock and survived less well than the parental strain. When 100 mM 3-hydroxybutyrate (3HB) was added to the medium, the Δ<jats:italic>phaC1</jats:italic> (<jats:italic>H. seropedicae</jats:italic> mutant unable to synthesise PHB) and Δ<jats:italic>phaZ1.2</jats:italic> (mutant unable to mobilise PHB) partially rescued heat adaptability (from 0 % survival without 3HB to 40 % of the initial viable population). Addition of 200 mM 3HB before the imposition of heat shock reduced protein aggregation to 15 % in Δ<jats:italic>phaC1</jats:italic> and 12 % in Δ<jats:italic>phaZ1.2</jats:italic>. We conclude that <jats:italic>H. seropedicae</jats:italic> SmR1 is naturally protected by 3HB released by PHB mobilisation, while mutants unable to generate high amounts of 3HB under heat shock conditions are less able to cope with heat damage.</jats:p> <jats:p><jats:bold>IMPORTANCE</jats:bold> Bacteria are subject to abrupt changes in environmental conditions for their growth, requiring rapid adaptation. Increasing the concentration of some metabolites can protect bacteria from hostile conditions that lead to protein denaturation and precipitation, and damage to plasma membranes as well. In this work, we demonstrated that under thermal shock the bacterium <jats:italic>Herbaspirillum seropedicae</jats:italic> depolymerised its intracellular stock polymer known as poly-3-hydroxybutyrate (PHB), rapidly increasing the concentration of 3-hydroxybutyrate (3HB), decreasing protein precipitation by thermal denaturation. Mutant <jats:italic>H. seropedicae</jats:italic> strains unable to produce PHB or to depolymerise it suffered irreparable damage during thermal shock, resulting in fast death when incubated at 45°C. Our results will contribute to the development of bacteria better adapted to high temperatures found either in natural conditions or in industrial processes. In the case of <jats:italic>H. seropedicae</jats:italic> and other bacteria that interact beneficially with plants, the understanding of PHB metabolism can be decisive for the development of more competitive strains and their application as biofertilisers in agriculture.</jats:p>

The protective role of PHB and its degradation products against stress situations in bacteria

“…Similarly, the ∆phaC mutant of R. eutropha is reported to be more sensitive to low temperature than the wild type (Nowroth et al 2016). Alves et al (2020) demonstrated that PHB mobilization is the key to survival of H.…”

“…Furthermore, mobilization of PHB in H. seropedicae SmR1 was activated by a heat shock at 45°C, and mutants that lacked the capacity to synthesize or mobilize PHB were more susceptible to heat shock (Alves et al 2020). Recent results showed that Pseudomonas extremaustralis, a highly stress-resistant strain, exhibits a high UV radiation resistance in conditions favoring PHB accumulation.…”

“…Beyond the eminent biotechnological potential as bioplastics with similar physicochemical properties to petrochemical materials, while highly degradable in the environment, PHB has been demonstrated to be a critical biopolymer for microbial physiology (Kim et al 2013;Alves et al 2016;Koskimäki et al 2016;Nowroth et al 2016;Batista et al 2018). Several studies have associated PHB synthesis and degradation to positive fitness in bacteria and protection against abiotic and biotic stressors (Ayub et al 2009;Nowroth et al 2016;Madueño et al 2018;Obruca et al 2018;Alves et al 2020;Tribelli et al 2020). Herein, we present an overview of the biogenesis of PHB granules and their protective role against stressors, the stress-relieving mechanisms, and recent data on how bacteria control the cycle of PHB synthesis and degradation, opening an important window of opportunity to engineer unique microbes for bioprocesses, bioremediation of pollutants, and biofertilization of plants.…”

Cyanobacterium Synechocystis sp. PCC 6803 lacking adc1 gene produces higher polyhydroxybutyrate accumulation under modified nutrients of acetate supplementation and nitrogen-phosphorus starvation

“…PCC 6803 [ 22 , 27 ]. Secondly, the environmental stresses could induce PHB production in microorganisms by supporting bacterial viability under adverse environments, such as heat stress, oxidative stress, high salinity [ 2 , 3 , 7 , 28 ]. Third strategy relates to genetic and/or metabolic engineering approach.…”

The First Insight into Polyhydroxyalkanoates Accumulation in Multi-Extremophilic Rubrobacter xylanophilus and Rubrobacter spartanus

“…From a biological point of view, the main purpose of PHA in bacterial cells is the storage of carbon and energy. Furthermore, it has been recently reported that the presence of PHA granules, as well as a complex PHA metabolism, can also enhance the robustness and resistance of bacterial cells to numerous stress factors, such as fluctuations in osmotic pressure [ 14 ], heating [ 15 ], freezing-thawing [ 16 ], UV irradiation [ 17 ], or oxidative pressure [ 18 ]. Actually, several very recent reviews are dedicated to the stress-protective function of PHA for prokaryotic cells [ 19 , 20 ].…”