The Bacillus subtilis PriA winged helix domain is critical for surviving DNA damage

Comparative genomics-based insights into Pantoea ananatis strains, isolated from white spot diseased leaves of maize with plant growth-promoting attributes

Pantoea ananatis is a member of the Enterobacteriaceae family known for its broad host adaptability. This study isolated 10 P. ananatis strains from white spot (MWS)-diseased leaves of maize (Zea mays) grown in Yunnan Province, China, and analyzed their putative functions, genomic diversity, and variation. The inoculation tests revealed that none of the 10 isolates caused MWS symptoms in maize. Nine maize isolates, except for S47, induced a hypersensitive response (HR) in tobacco and caused rot symptoms in onion. Most isolates exhibited plant growth-promoting characteristics, with strains JCC14, JCY1, and S47 significantly enhancing maize seedling growth parameters. Genomic sequencing of 10 maize isolates and two rice isolates revealed that 12 isolates clustered into three groups, with an open pan-genome identified. Ancestral reconstruction indicated that the genome size increased in Group A and then decreased in Group B, with significant gains in orthologous groups at Node 14, the most recent common ancestor (MRCA) of Group A and Group B, and at Node 19, the MRCA of seven maize-isolated strains and other Group B strains. Additionally, 11 single-copy orthologous groups were under positive selection. Furthermore, the HIVir (high virulence, also known as PASVIL, P. ananatis-specific virulence locus) cluster and type VI secretion system-related genes were conserved in certain P. ananatis strains but were not related to their group divergences. This study not only reveals the diverse functions of MWS-diseased maize P. ananatis isolates, but also enhances our understanding of divergent genome evolution and environmental adaptation across P. ananatis species.IMPORTANCEPantoea ananatis is a bacterium commonly found in various agronomic crops. Maize white spot (MWS) has been one of the most destructive diseases affecting maize, leading to significant economic losses. This study clarified that P. ananatis strains colonized maize leaves but were not the causal agents of MWS in Yunnan Province, China. Moreover, most of these P. ananatis strains exhibited plant growth-promoting (PGP) activities, induced hypersensitive response (HR) activity on tobacco, and caused rot symptoms in onion. Notably, the analysis of divergence throughout the evolutionary process revealed significant genomic evolution and environmental adaptation in these P. ananatis strains. This highlights the genetic exchange that has shaped the genome of P. ananatis. These findings improve our understanding of the functional diversity of P. ananatis strains across different hosts and their positions within the evolutionary lineages of P. ananatis species.

UV-C and hydration state drive pulsed light-induced proteome damage in Bacillus pumilus spores

Introduction

Pulsed light (PL) is a non-thermal processing technology that inactivates microorganisms through high-intensity pulses of polychromatic light, including ultraviolet-C (UV-C). While the germicidal effect of PL has been widely studied, its impact on microbial proteomes remains poorly understood. Here, we investigate the proteomic response of Bacillus pumilus DSM492 (ATCC 27142) spores to PL treatment, comparing it to conventional UV-C 254 nm exposure.

Methods

B. pumilus spores were either suspended in water or sprayed onto a polystyrene surface and exposed to PL or UV-C at fluences achieving a 5-log and a > 7-log reduction in viability. Proteomic changes were analyzed using mass spectrometry to identify proteins with decreased abundance after treatment.

Results

PL treatment induced a significantly greater proteomic alteration compared to UV-C, particularly in spores suspended in water, where the number of proteins with decreased abundance was ~6-fold higher than in spores sprayed on a polystyrene surface. Proteomic analysis revealed that the effect of PL in water was primarily due to UV-C 254 nm, whereas on polystyrene, UV-C 254 nm had no significant impact. Furthermore, proteins most affected by PL were enriched in photosensitive amino acids such as tryptophan, histidine, tyrosine, cysteine, and methionine, suggesting oxidation and photoreactivity as key degradation mechanisms.

Discussion

Although the overall inactivation rate could not be directly correlated with proteome damage, we identified that core proteins involved in DNA and RNA protection and repair were specifically targeted by PL. These findings provide new insights into the molecular mechanisms underlying PL-mediated microbial inactivation and highlight the role of protein photodamage in spore susceptibility.

Processing of stalled replication forks in Bacillus subtilis

Accurate DNA replication and transcription elongation are crucial for preventing the accumulation of unreplicated DNA and genomic instability. Cells have evolved multiple mechanisms to deal with impaired replication fork progression, challenged by both intrinsic and extrinsic impediments. The bacterium Bacillus subtilis, which adopts multiple forms of differentiation and development, serves as an excellent model system for studying the pathways required to cope with replication stress to preserve genomic stability. This review focuses on the genetics, single molecule choreography, and biochemical properties of the proteins that act to circumvent the replicative arrest allowing the resumption of DNA synthesis. The RecA recombinase, its mediators (RecO, RecR, and RadA/Sms) and modulators (RecF, RecX, RarA, RecU, RecD2, and PcrA), repair licensing (DisA), fork remodelers (RuvAB, RecG, RecD2, RadA/Sms, and PriA), Holliday junction resolvase (RecU), nucleases (RnhC and DinG), and translesion synthesis DNA polymerases (PolY1 and PolY2) are key functions required to overcome a replication stress, provided that the fork does not collapse.

Can antimicrobial blue light contribute to resistance development? Genome-wide analysis revealed aBL-protective genes in Escherichia coli

IMPORTANCE

Increasing antibiotic resistance and the lack of new antibiotic-like compounds to combat bacterial resistance are significant problems of modern medicine. The development of new alternative therapeutic strategies is extremely important. Antimicrobial blue light (aBL) is an innovative approach to combat multidrug-resistant microorganisms. aBL has a multitarget mode of action; however, the full mechanism of aBL antibacterial action requires further investigation. In addition, the potential risk of resistance development to this treatment should be considered.

Limited Role of Rhamnolipids on Cadmium Resistance for an Endogenous-Secretion Bacterium

Rhamnolipids, a type of biosurfactant, represent a potential strategy for both enhancing organismic resistance and in situ remediation of heavy metals contaminations. In-depth study of the mechanism of rhamnolipids synthesis in response to heavy metals stress, is indispensable for a wide use of biosurfactant-secreting microbes in bioremediation. In this study, we employed the wild-type and the rhlAB deficient strain (ΔrhlAB) of Pseudomonas aeruginosa, a prototypal rhamnolipids-producing soil microorganism, to investigate its responses to cadmium resistance based on its physicochemical, and physiological properties. Compared with the wild-type strain, the ΔrhlAB were more sensitive to Cd-stress at low Cd concentration (<50 mg/L), whereas there was little difference in sensitivity at higher Cd concentrations, as shown by spot titers and cell viability assays. Secreted rhamnolipids reduced intracellular Cd²⁺ accumulation to alleviate Cd²⁺ stress, whereas endogenous rhamnolipids played a limited role in alleviating Cd²⁺ stress. Synthesized rhamnolipids exhibited a higher critical micelle concentration (CMC) (674.1 mg/L) and lower emulsification index (4.7%) under high Cd-stress, while these parameters showed no obvious changes. High Cd-stress resulted in high hydrophilic wild-type bacterial surface and lower bioremediation ability. This study could advance a deeper understanding of the mechanism of cadmium resistance and provide a theoretical foundation for the application of biosurfactant and biosurfactant-secreted bacterium in contaminant bioremediation.