Transcriptional response of Bacillus megaterium FDU301 to PEG200-mediated arid stress

Metabolic and protein expression responses of Shewanella baltica in golden pomfret broths to slightly acidic electrolysed water

Shewanella baltica is a specific spoilage organism of golden pomfret. This study aims to explore the antibacterial mechanism of slightly acidic electrolysed water (SAEW) against S. baltica (strains ABa4, ABe2 and BBe1) in golden pomfret broths by metabolomics, proteomics and bioinformatics analyses. S. baltica was decreased by at least 3.94 log CFU/mL after SAEW treatment, and strain ABa4 had the highest resistance. Under SAEW stress, amino acids and organic acids in S. baltica decreased, and nucleotide related compounds degraded. Furthermore, 100 differentially expressed proteins (DEPs) were identified. Most DEPs of strains ABe2 and BBe1 were down-regulated, while some DEPs of strain ABa4 were up-regulated, especially those oxidative stress related proteins. These results suggest that the modes of SAEW against S. baltica can be traced to the inhibition of amino acid, carbon, nucleotide and sulphur metabolisms, and the loss of functional proteins for temperature regulation, translation, motility and protein folding.

Biofouling behaviors of reverse osmosis membrane in the presence of trace plasticizer for circulating cooling water treatment: Characteristics and mechanisms

Reverse osmosis (RO) system has been increasingly applied for circulating cooling water (CCW) reclamation. Plasticizers, which may be dissolved into CCW system in plastic manufacturing industry, cannot be completely removed by the pretreatment prior to RO system, possibly leading to severe membrane biofouling. Deciphering the characteristics and mechanisms of RO membrane biofouling in the presence of trace plasticizers are of paramount importance to the development of effective fouling control strategies. Herein, we demonstrate that exposure to a low concentration (1 - 10 μg/L) of three typical plasticizers (Dibutyl phthalate (DBP), Tributyl phosphate (TBP) and 2,2,4-Trimethylpentane-1,3-diol (TMPD)) detected in pretreated real CCW promoted Escherichia coli biofilm formation. DBP, TBP and TMPD showed the highest stimulation at 5 or 10 μg/L with biomass increasing by 55.7 ± 8.2 %, 35.9 ± 9.5 % and 32.2 ± 14.7 % respectively, relative to the unexposed control. Accordingly, the bacteria upon exposure to trace plasticizers showed enhanced adenosine triphosphate (ATP) activity, stimulated extracellular polymeric substances (EPS) excretion and suppressed intracellular reactive oxygen species (ROS) induction, causing by upregulation of related genes. Long-term study further showed that the RO membranes flowing by the pretreated real CCW in a polypropylene plant exhibited a severer biofouling behavior than exposed control, and DBP and TBP parts played a key role in stimulation effects on bacterial proliferation. Overall, we demonstrate that RO membrane exposure to trace plasticizers in pretreated CCW can upregulate molecular processes and physiologic responses that accelerate membrane biofouling, which provides important implications for biofouling control strategies in membrane-based CCW treatment systems.

Proteomic investigation reveals the role of bacterial laccase from Bacillus pumilus in oxidative stress defense

The wide distribution of laccases in nature makes them involved in different biological processes. However, little information is known about how laccase participates in the defense machinery of bacteria against oxidative stress. The present study aimed to elucidate the oxidative stress response mechanism of Bacillus pumilus ZB1 and the functional role of bacterial laccase in stress defense. The oxidative stress caused by methyl methanesulfonate (MMS) significantly induced laccase activity and its transcript level. The morphological analysis revealed that the defense of B. pumilus ZB1 against oxidative stress was activated. Based on the proteomic study, 114 differentially expressed proteins (DEPs) were up-regulated and 79 DEPs were down-regulated. In COG analysis, 66.40% DEPs were classified into the category "Metabolism". We confirmed that laccase was up-regulated in response to MMS stress and its functional annotation was related to "Secondary metabolites biosynthesis, transport and catabolism". Based on protein-protein interaction prediction, two up-regulated DEPs (YcnJ and GabP) showed interaction with laccase and contributed to the formation of laccase stability and adaptability. The overexpressed laccase might improve the antioxidative property of B. pumilus ZB1. These findings provide an insight and the guidelines for better exploitation of bioremediation using bacterial laccase. SIGNIFICANCE: Bacillus pumilus is a gram-positive bacterium that has the potential for many applications, such as bioremediation. The expression of bacterial laccase is significantly influenced by oxidative stress, while the underlying mechanism of laccase overexpression in bacteria has not been fully studied. Elucidation of the biological process may benefit the bioremediation using bacteria in the future. In this study, the differentially expressed proteins were analyzed using a TMT-labeling proteomic approach when B. pumilus was treated with methyl methanesulfonate (MMS). Reactive oxygen species induced by MMS activated the secondary metabolites biosynthesis, transport, and catabolism in B. pumilus, including laccase overexpression. Moreover, the simultaneously up-regulated YcnJ and GabP may benefit the synthesis and the stability of laccase, then improve the antioxidative property of B. pumilus against environmental stress. Our findings advance the understanding of the adaptive mechanism of B. pumilus to environmental conditions.

Priestia megaterium Metabolism: Isolation, Identification of Naringenin Analogues and Genes Elevated Associated with Nanoparticle Intervention

The impact of gold nanoparticles (AuNPs) on the biosynthetic manipulation of Priestia megaterium metabolism where an existing gene cluster is enhanced to produce and enrich bioactive secondary metabolites has been studied previously. In this research, we aimed to isolate and elucidate the structure of metabolites of compounds 1 and 2 which have been analyzed previously in P. megaterium crude extract. This was achieved through a PREP-ODS C18 column with an HPLC-UV/visible detector. Then, the compounds were subjected to nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), and Fourier-transform infrared spectroscopy (FT-IR) techniques. Furthermore, bioinformatics and transcriptome analysis were used to examine the gene expression for which the secondary metabolites produced in the presence of AuNPs showed significant enhancement in transcriptomic responses. The metabolites of compounds 1 and 2 were identified as daidzein and genistein, respectively. The real-time polymerase chain reaction (RT-PCR) technique was used to assess the expression of three genes (csoR, CHS, and yjiB) from a panel of selected genes known to be involved in the biosynthesis of the identified secondary metabolites. The expression levels of two genes (csoR and yijB) increased in response to AuNP intervention, whereas CHS was unaffected.

A Sporulation-Independent Way of Life for Bacillus thuringiensis in the Late Stages of an Infection

The formation of endospores has been considered the unique survival and transmission mode of sporulating Firmicutes due to the exceptional resistance and persistence of this bacterial form. However, nonsporulated bacteria (Spo^-) were reported at the early stages following the death of a host infected with Bacillus thuringiensis, an entomopathogenic sporulating bacterium. Here, we investigated the characteristics of the bacterial population in the late stages of an infection in the B. thuringiensis/Galleria mellonella infection model. Using fluorescent reporters and molecular markers coupled to flow cytometry, we demonstrated that the Spo^- cells persist and constitute about half of the population 2 weeks post-infection (p.i.). Protein synthesis and growth recovery assays indicated that they are in a metabolically slowed-down state. These bacteria were extremely resistant to the insect cadaver environment, which did not support growth of in vitro-grown vegetative cells and spores. A transcriptomic analysis of this subpopulation at 7 days p.i. revealed a signature profile of this state, and the expression analysis of individual genes at the cell level showed that more bacteria mount an oxidative stress response as their survival time increases, in agreement with the increase of the free radical level in the host cadaver and in the number of reactive oxygen species (ROS)-producing bacteria. Altogether, these data show for the first time that nonsporulated bacteria are able to survive for a prolonged period of time in the context of an infection and indicate that they engage in a profound adaptation process that leads to their persistence in the host cadaver. IMPORTANCE Bacillus thuringiensis is an entomopathogenic bacterium widely used as a biopesticide. It belongs to the Bacillus cereus group, comprising the foodborne pathogen B. cereus sensu stricto and the anthrax agent Bacillus anthracis. Like other Firmicutes when they encounter harsh conditions, these Gram-positive bacteria can form dormant cells called spores. Due to its highly resistant nature, the spore was considered the unique mode of long-term survival, eclipsing any other form of persistence. Breaking this paradigm, we observed that B. thuringiensis was able to persist in its host cadaver in a nonsporulated form for at least 14 days. Our results show that these bacteria survived in the cadaver environment, which proved hostile for actively growing bacteria by engaging in a profound adaptation process. Studying this facet of the life cycle of a sporulating bacterium provides new fundamental knowledge and might lead to the development of strategies to combat sporulating pathogenic species.

A Plant Endophytic Bacterium Priestia megaterium StrainBP-R2 Isolated from the Halophyte Bolboschoenus planiculmis Enhances Plant Growth under Salt and Drought Stresses

Global warming and climate change have contributed to the rise of weather extremes. Severe drought and soil salinization increase because of rising temperatures. Economically important crop production and plant growth and development are hindered when facing various abiotic stresses. Plant endophytic bacteria live inside host plants without causing visible harm and can be isolated from surface-sterilized plant tissues. Using plant endophytic bacteria to stimulate plant growth and increase environmental stress tolerance has become an alternative approach besides using the traditional breeding and genetically modifying approaches to select or create new crop types resistant to different environmental stresses. The plant endophytic bacterium, Priestia megaterium (previously known as Bacillus megaterium) strain BP-R2, was isolated from the surface-sterilized root tissues of the salt marsh halophyte Bolboschoenus planiculmis. The bacteria strain BP-R2 showed high tolerance to different sodium chloride (NaCl) concentrations and produced the auxin plant hormone, indole acetic acid (IAA), under various tested growth conditions. Inoculation of Arabidopsis and pak choi (Brassica rapa L. R. Chinensis Group) plants with the strain BP-R2 greatly enhanced different growth parameters of the host plants under normal and salt and drought stress conditions compared to that of the mock-inoculated plants. Furthermore, the hydrogen peroxide (H₂O₂) content, electrolyte leakage (EL), and malondialdehyde (MDA) concentration accumulated less in the BP-R2-inoculated plants than in the mock-inoculated control plants under salt and drought stresses. In summary, the plant endophytic bacterium strain BP-R2 increased host plant growth and stress tolerance to salt and drought conditions.

Transcriptional response of the xerotolerant Arthrobacter sp. Helios strain to PEG-induced drought stress

A new bacterial strain has been isolated from the microbiome of solar panels and classified as Arthrobacter sp. Helios according to its 16S rDNA, positioning it in the “Arthrobacter citreus group.” The isolated strain is highly tolerant to desiccation, UV radiation and to the presence of metals and metalloids, while it is motile and capable of growing in a variety of carbon sources. These characteristics, together with observation that Arthrobacter sp. Helios seems to be permanently prepared to handle the desiccation stress, make it very versatile and give it a great potential to use it as a biotechnological chassis. The new strain genome has been sequenced and its analysis revealed that it is extremely well poised to respond to environmental stresses. We have analyzed the transcriptional response of this strain to PEG6000-mediated arid stress to investigate the desiccation resistance mechanism. Most of the induced genes participate in cellular homeostasis such as ion and osmolyte transport and iron scavenging. Moreover, the greatest induction has been found in a gene cluster responsible for biogenic amine catabolism, suggesting their involvement in the desiccation resistance mechanism in this bacterium.

High Proportions of Radiation-Resistant Strains in Culturable Bacteria from the Taklimakan Desert

Simple Summary

Radiation-resistant extremophiles have frequently been found in the Taklimakan Desert, which is known for its harsh conditions. However, there is no systemic study investigating the diversity and proportion of radiation-resistant strains among culturable bacteria. The results of this study revealed the distribution of culturable bacteria in the Taklimakan Desert and indicated high proportions of radiation-resistant strains in the culturable bacteria. The study helps to better understand the ecological origin of radio-resistance and to quantitatively describe the desert as a common habitat for radiation-resistant extremophiles.

Abstract

The Taklimakan Desert located in China is the second-largest shifting sand desert in the world and is known for its harsh conditions. Types of γ-rays or UV radiation-resistant bacterial strains have been isolated from this desert. However, there is no information regarding the proportions of the radiation-resistant strains in the total culturable microbes. We isolated 352 bacterial strains from nine sites across the Taklimakan Desert from north to south. They belong to Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes. The phylum Actinobacteria was the most predominant in abundance and Firmicutes had the highest species richness. Bacteroidetes had the lowest abundance and was found in four sites only, while the other three phyla were found in every site but with different distribution profiles. After irradiating with 1000 J/m² and 6000 J/m² UV-C, the strains with survival rates higher than 10% occupied 72.3% and 36.9% of all culturable bacteria, respectively. The members from Proteobacteria had the highest proportions, with survival rates higher than 10%. After radiation with 10 kGy γ-rays, Kocuria sp. TKL1057 and Planococcus sp. TKL1152 showed higher radiation-resistant capabilities than Deinococcus radiodurans R1. Besides obtaining several radiation-resistant extremophiles, this study measured the proportions of the radiation-resistant strains in the total culturable microbes for the first time. This study may help to better understand the origin of radioresistance, especially by quantitatively comparing proportions of radiation-resistant extremophiles from different environments in the future.