The cold shock family gene cspD3 is involved in the pathogenicity of Ralstonia solanacearum CQPS-1 to tobacco

Role of cold shock proteins B and D in Aeromonas salmonicida subsp. salmonicida physiology and virulence in lumpfish (Cyclopterus lumpus)

Cold shock proteins (Csp) are pivotal nucleic acid binding proteins known for their crucial roles in the physiology and virulence of various bacterial pathogens affecting plant, insect, and mammalian hosts. However, their significance in bacterial pathogens of teleost fish remains unexplored. Aeromonas salmonicida subsp. salmonicida (hereafter A. salmonicida) is a psychrotrophic pathogen and the causative agent of furunculosis in marine and freshwater fish. Four csp genes (cspB, cspD, cspA, and cspC) have been identified in the genome of A. salmonicida J223 (wild type). Here, we evaluated the role of DNA binding proteins, CspB and CspD, in A. salmonicida physiology and virulence in lumpfish (Cyclopterus lumpus). A. salmonicida ΔcspB, ΔcspD, and the double ΔcspBΔcspD mutants were constructed and characterized. A. salmonicida ΔcspB and ΔcspBΔcspD mutants showed a faster growth at 28°C, and reduced virulence in lumpfish. A. salmonicida ΔcspD showed a slower growth at 28°C, biofilm formation, lower survival in low temperatures and freezing conditions (-20°C, 0°C, and 4°C), deficient in lipopolysaccharide synthesis, and low virulence in lumpfish. Additionally, ΔcspBΔcspD mutants showed less survival in the presence of bile compared to the wild type. Transcriptome analysis revealed that 200, 37, and 921 genes were differentially expressed in ΔcspB, ΔcspD, and ΔcspBΔcspD, respectively. In ΔcspB and ΔcspBΔcspD virulence genes in the chromosome and virulence plasmid were downregulated. Our analysis indicates that CspB and CspD mostly act as a transcriptional activator, influencing cell division (e.g., treB), virulence factors (e.g., aexT), and ultimately virulence.

Natural variation of immune epitopes reveals intrabacterial antagonism

Plants and animals detect biomolecules termed microbe-associated molecular patterns (MAMPs) and induce immunity. Agricultural production is severely impacted by pathogens which can be controlled by transferring immune receptors. However, most studies use a single MAMP epitope and the impact of diverse multicopy MAMPs on immune induction is unknown. Here, we characterized the epitope landscape from five proteinaceous MAMPs across 4,228 plant-associated bacterial genomes. Despite the diversity sampled, natural variation was constrained and experimentally testable. Immune perception in both Arabidopsis and tomato depended on both epitope sequence and copy number variation. For example, Elongation Factor Tu is predominantly single copy, and 92% of its epitopes are immunogenic. Conversely, 99.9% of bacterial genomes contain multiple cold shock proteins, and 46% carry a nonimmunogenic form. We uncovered a mechanism for immune evasion, intrabacterial antagonism, where a nonimmunogenic cold shock protein blocks perception of immunogenic forms encoded in the same genome. These data will lay the foundation for immune receptor deployment and engineering based on natural variation.

Natural variation of immune epitopes reveals intrabacterial antagonism

Plants and animals detect biomolecules termed Microbe-Associated Molecular Patterns (MAMPs) and induce immunity. Agricultural production is severely impacted by pathogens which can be controlled by transferring immune receptors. However, most studies use a single MAMP epitope and the impact of diverse multi-copy MAMPs on immune induction is unknown. Here we characterized the epitope landscape from five proteinaceous MAMPs across 4,228 plant-associated bacterial genomes. Despite the diversity sampled, natural variation was constrained and experimentally testable. Immune perception in both Arabidopsis and tomato depended on both epitope sequence and copy number variation. For example, Elongation Factor Tu is predominantly single copy and 92% of its epitopes are immunogenic. Conversely, 99.9% of bacterial genomes contain multiple Cold Shock Proteins and 46% carry a non-immunogenic form. We uncovered a new mechanism for immune evasion, intrabacterial antagonism, where a non-immunogenic Cold Shock Protein blocks perception of immunogenic forms encoded in the same genome. These data will lay the foundation for immune receptor deployment and engineering based on natural variation.

From Stress Tolerance to Virulence: Recognizing the Roles of Csps in Pathogenicity and Food Contamination

Be it for lab studies or real-life situations, bacteria are constantly exposed to a myriad of physical or chemical stresses that selectively allow the tolerant to survive and thrive. In response to environmental fluctuations, the expression of cold shock domain family proteins (Csps) significantly increases to counteract and help cells deal with the harmful effects of stresses. Csps are, therefore, considered stress adaptation proteins. The primary functions of Csps include chaperoning nucleic acids and regulating global gene expression. In this review, we focus on the phenotypic effects of Csps in pathogenic bacteria and explore their involvement in bacterial pathogenesis. Current studies of csp deletions among pathogenic strains indicate their involvement in motility, host invasion and stress tolerance, proliferation, cell adhesion, and biofilm formation. Through their RNA chaperone activity, Csps regulate virulence-associated genes and thereby contribute to bacterial pathogenicity. Additionally, we outline their involvement in food contamination and discuss how foodborne pathogens utilize the stress tolerance roles of Csps against preservation and sanitation strategies. Furthermore, we highlight how Csps positively and negatively impact pathogens and the host. Overall, Csps are involved in regulatory networks that influence the expression of genes central to stress tolerance and virulence.

Mutation in phcA Enhanced the Adaptation of Ralstonia solanacearum to Long-Term Acid Stress

Bacterial wilt, caused by the plant pathogen Ralstonia solanacearum, occurs more severely in acidified soil according to previous reports. However, R. solanacearum cannot grow well in acidic environments under barren nutrient culture conditions, especially when the pH is lower than 5. With the worsening acidification of farmland, further determination of how R. solanacearum adapts to the long-term acidic environment is worthwhile. In this study, experimental evolution was applied to evaluate the adaptability and mechanism of the R. solanacearum experimental population responding to long-term acid stress. We chose the CQPS-1 strain as the ancestor, and minimal medium (MM medium) with different pH values as the culture environment to simulate poor soil. After 1500 generations of serial passage experiments in pH 4.9 MM, acid-adapted experimental strains (denoted as C49 strains) were obtained, showing significantly higher growth rates than the growth rates of control experimental strains (serial passage experiment in pH 6.5 MM, denoted as C65 strains). Competition experiments showed that the competitive indices (CIs) of all selected clones from C49 strains were superior to the ancestor in acidic environment competitiveness. Based on the genome variation analysis and functional verification, we confirmed that loss of function in the phcA gene was associated with the acid fitness gain of R. solanacearum, which meant that the inactivation of the PhcA regulator caused by gene mutation mediated the population expansion of R. solanacearum when growing in an acidic stress environment. Moreover, the swimming motility of acid evolution strains and the phcA deletion mutant was significantly enhanced compared to CQPS-1. This work provided evidence for understanding the adaptive strategy of R. solanacearum to the long-term acidic environment.

Regulated strategies of cold-adapted microorganisms in response to cold: a review

There are a large number of active cold-adapted microorganisms in the perennial cold environment. Due to their high-efficiency and energy-saving catalytic properties, cold-adapted microorganisms have become valuable natural resources with potential in various biological fields. In this study, a series of cold response strategies for microorganisms were summarized. This mainly involves the regulation of cell membrane fluidity, synthesis of cold adaptation proteins, regulators and metabolic changes, energy supply, and reactive oxygen species. Also, the potential of biocatalysts produced by cold-adapted microorganisms including cold-active enzymes, ice-binding proteins, polyhydroxyalkanoates, and surfactants was introduced, which provided a guidance for expanding its application values. Overall, new insights were obtained on response strategies of microorganisms to cold environments in this review. This will deepen the understanding of the cold tolerance mechanism of cold-adapted microorganisms, thus promoting the establishment and application of low-temperature biotechnology.

Mobile genetic elements mediate the mixotrophic evolution of novel Alicyclobacillus species for acid mine drainage adaptation

Alicyclobacillus species inhabit diverse environments and have adapted to broad ranges of pH and temperature. However, their adaptive evolutions remain elusive, especially regarding the role of mobile genetic elements (MGEs). Here, we characterized the distributions and functions of MGEs in Alicyclobacillus species across five environments, including acid mine drainage (AMD), beverages, hot springs, sediments, and soils. Nine Alicyclobacillus strains were isolated from AMD and possessed larger genome sizes and more genes than those from other environments. Four AMD strains evolved to be mixotrophic and fell into distinctive clusters in phylogenetic tree. Four types of MGEs including genomic island (GI), insertion sequence (IS), prophage, and integrative and conjugative element (ICE) were widely distributed in Alicyclobacillus species. Further, AMD strains did not possess CRISPR-Cas systems, but had more GI, IS, and ICE, as well as more MGE-associated genes involved in the oxidation of iron and sulfide and the resistance of heavy metal and low temperature. These findings highlight the differences in phenotypes and genotypes between strains isolated from AMD and other environments and the important role of MGEs in rapid environment niche expansions.