A census of membrane-bound and intracellular signal transduction proteins in bacteria: bacterial IQ, extroverts and introverts

The primary carbon metabolism in cyanobacteria and its regulation

Cyanobacteria are the only prokaryotes capable of performing oxygenic photosynthesis. Many cyanobacterial strains can live in different trophic modes, ranging from photoautotrophic and heterotrophic to mixotrophic growth. However, the regulatory mechanisms allowing a flexible switch between these lifestyles are poorly understood. As anabolic fixation of CO2 in the Calvin-Benson-Bassham (CBB) cycle and catabolic sugar-degradation pathways share intermediates and enzymatic capacity, a tight regulatory network is required to enable simultaneous opposed metabolic fluxes. The Entner-Doudoroff (ED) pathway was recently predicted as one glycolytic route, which cooperates with other pathways in glycogen breakdown. Despite low carbon flux through the ED pathway, metabolite analyses of mutants deficient in the ED pathway revealed a distinct phenotype pointing at a strong regulatory impact of this route. The small Cp12 protein downregulates the CBB cycle in darkness by inhibiting phosphoribulokinase and glyceraldehyde 3-phosphate dehydrogenase. New results of metabolomic and redox level analyses on strains with Cp12 variants extend the known role of Cp12 regulation towards the acclimation to external glucose supply under diurnal conditions as well as to fluctuations in CO2 levels in the light. Moreover, carbon and nitrogen metabolism are closely linked to maintain an essential C/N homeostasis. The small protein PirC was shown to be an important regulator of phosphoglycerate mutase, which identified this enzyme as central branching point for carbon allocation from CBB cycle towards lower glycolysis. Altered metabolite levels in the mutant ΔpirC during nitrogen starvation experiments confirm this regulatory mechanism. The elucidation of novel mechanisms regulating carbon allocation at crucial metabolic branching points could identify ways for targeted redirection of carbon flow towards desired compounds, and thus help to further establish cyanobacteria as green cell factories for biotechnological applications with concurrent utilization of sunlight and CO2.

Tailoring regulatory components for metabolic engineering in cyanobacteria

The looming climate crisis has prompted an ever-growing interest in cyanobacteria due to their potential as sustainable production platforms for the synthesis of energy carriers and value-added chemicals from CO2 and sunlight. Nonetheless, cyanobacteria are yet to compete with heterotrophic systems in terms of space-time yields and consequently production costs. One major drawback leading to the low production performance observed in cyanobacteria is the limited ability to utilize the full capacity of the photosynthetic apparatus and its associated systems, i.e. CO2 fixation and the directly connected metabolism. In this review, novel insights into various levels of metabolic regulation of cyanobacteria are discussed, including the potential of targeting these regulatory mechanisms to create a chassis with a phenotype favorable for photoautotrophic production. Compared to conventional metabolic engineering approaches, minor perturbations of regulatory mechanisms can have wide-ranging effects.

Changes in bacterial community composition in the uterus of Holstein cow with endometritis before and after treatment with oxytetracycline

It is important to study the bacteria that cause endometritis to identify effective therapeutic drugs for dairy cows. In this study, 20% oxytetracycline was used to treat Holstein cows (n = 6) with severe endometritis. Additional 10 Holstein cows (5 for healthy cows, 5 for cows with mild endometritis) were also selected. At the same time, changes in bacterial communities were monitored by high-throughput sequencing. The results show that Escherichia coli, Staphylococcus aureus and other common pathogenic bacteria could be detected by traditional methods in cows both with and without endometritis. However, 16S sequencing results show that changes in the abundance of these bacteria were not significant. Endometritis is often caused by mixed infections in the uterus. Oxytetracycline did not completely remove existing bacteria. However, oxytetracycline could effectively inhibit endometritis and had a significant inhibitory effect on the genera Bacteroides, Trueperella, Peptoniphilus, Parvimonas, Porphyromonas, and Fusobacterium but had no significant inhibitory effect on the bacterial genera Marinospirillum, Erysipelothrix, and Enteractinococcus. During oxytetracycline treatment, the cell motility, endocrine system, exogenous system, glycan biosynthesis and metabolism, lipid metabolism, metabolism of terpenoids, polyketides, cofactors and vitamins, signal transduction, and transport and catabolism pathways were affected.

Comprehensive virulence profiling and evolutionary analysis of specificity determinants in Staphylococcus aureus two-component systems

In the Staphylococcus aureus genome, a set of highly conserved two-component systems (TCSs) composed of histidine kinases (HKs) and their cognate response regulators (RRs) sense and respond to environmental stimuli, which drive the adaptation of the bacteria. This study investigates the complex interplay between TCSs in S. aureus USA300, a predominant methicillin-resistant S. aureus strain, revealing shared and unique virulence regulatory pathways and genetic variations mediating signal specificity within TCSs. Using TCS-related mutants from the Nebraska Transposon Mutant Library, we analyzed the effects of inactivated TCS HKs and RRs on the production of various virulence factors, in vitro infection abilities, and adhesion assays. We found that the TCSs' influence on virulence determinants was not associated with their phylogenetic relationship, indicating divergent functional evolution. Using the co-crystallized structure of the DesK-DesR from Bacillus subtilis and the modeled structures of the four NarL TCSs in S. aureus, we identified interacting residues, revealing specificity determinants and conservation within the same TCS, even from different strain backgrounds. The interacting residues were highly conserved within strains but varied between species due to selection pressures and the coevolution of cognate pairs. This study unveils the complex interplay and divergent functional evolution of TCSs, highlighting their potential for future experimental exploration of phosphotransfer between cognate and non-cognate recombinant HK and RRs.IMPORTANCEGiven the widespread conservation of two-component systems (TCSs) in bacteria and their pivotal role in regulating metabolic and virulence pathways, they present a compelling target for anti-microbial agents, especially in the face of rising multi-drug-resistant infections. Harnessing TCSs therapeutically necessitates a profound understanding of their evolutionary trajectory in signal transduction, as this underlies their unique or shared virulence regulatory pathways. Such insights are critical for effectively targeting TCS components, ensuring an optimized impact on bacterial virulence, and mitigating the risk of resistance emergence via the evolution of alternative pathways. Our research offers an in-depth exploration of virulence determinants controlled by TCSs in S. aureus, shedding light on the evolving specificity determinants that orchestrate interactions between their cognate pairs.

Microbial sensor variation across biogeochemical conditions in the terrestrial deep subsurface

Microbes can be found in abundance many kilometers underground. While microbial metabolic capabilities have been examined across different geochemical settings, it remains unclear how changes in subsurface niches affect microbial needs to sense and respond to their environment. To address this question, we examined how microbial extracellular sensor systems vary with environmental conditions across metagenomes at different Deep Mine Microbial Observatory (DeMMO) subsurface sites. Because two-component systems (TCSs) directly sense extracellular conditions and convert this information into intracellular biochemical responses, we expected that this sensor family would vary across isolated oligotrophic subterranean environments that differ in abiotic and biotic conditions. TCSs were found at all six subsurface sites, the service water control, and the surface site, with an average of 0.88 sensor histidine kinases (HKs) per 100 genes across all sites. Abundance was greater in subsurface fracture fluids compared with surface-derived fluids, and candidate phyla radiation (CPR) bacteria presented the lowest HK frequencies. Measures of microbial diversity, such as the Shannon diversity index, revealed that HK abundance is inversely correlated with microbial diversity (r2 = 0.81). Among the geochemical parameters measured, HK frequency correlated most strongly with variance in dissolved organic carbon (r2 = 0.82). Taken together, these results implicate the abiotic and biotic properties of an ecological niche as drivers of sensor needs, and they suggest that microbes in environments with large fluctuations in organic nutrients (e.g., lacustrine, terrestrial, and coastal ecosystems) may require greater TCS diversity than ecosystems with low nutrients (e.g., open ocean).IMPORTANCEThe ability to detect extracellular environmental conditions is a fundamental property of all life forms. Because microbial two-component sensor systems convert information about extracellular conditions into biochemical information that controls their behaviors, we evaluated how two-component sensor systems evolved within the deep Earth across multiple sites where abiotic and biotic properties vary. We show that these sensor systems remain abundant in microbial consortia at all subterranean sampling sites and observe correlations between sensor system abundances and abiotic (dissolved organic carbon variation) and biotic (consortia diversity) properties. These results suggest that multiple environmental properties may drive sensor protein evolution and highlight the need for further studies of metagenomic and geochemical data in parallel to understand the drivers of microbial sensor evolution.

Principles of cognitive biology and the concept of biocivilisations

A range of studies published in the last few decades promotes the cognitive aspects of life: all organisms, from bacteria to mammals, are capable of sensing/perception, decision-making, problem-solving, learning, and other cognitive functions, including sentience and consciousness. In this paper I present a scientific and philosophical synthesis of these studies, leading to an integrated view of cognitive biology. This view is expressed through the four principles applicable to all living systems: (1) sentience and consciousness, (2) autopoiesis, (3) free energy principle and relational biology, and (4) cognitive repertoire. The principles are circular, and they reinforce themselves. The circularity is not rigid, meaning that hierarchical and heterarchical shifts are widespread in the biosphere. The above principles emerged at the dawn of life, with the first cells, bacteria and archaea. All biogenic forms and functions that emerged since then can be traced to the first cells - indivisible units of biological agency. Following these principles, I developed the concept of biocivilisations to explain various forms of social intelligence in different kingdoms of life. The term biociviloisations draws on the human interpretation of the concept of civilisation, which searches for non-human equivalents of communication, engineering, science, medicine, art, and agriculture, in all kingdoms of life by applying the principles of cognitive biology. Potential avenues for testing the concept of biocivilisations are highlighted.

REC protein family expansion by the emergence of a new signaling pathway

IMPORTANCE

We explore when and why large classes of proteins expand into new sequence space. We used an unsupervised machine learning approach to observe the sequence landscape of REC domains of bacterial response regulator proteins. We find that within-gene recombination can switch effector domains and, consequently, change the regulatory context of the duplicated protein.

Genome features of a novel hydrocarbonoclastic Chryseobacterium oranimense strain and its comparison to bacterial oil-degraders and to other C. oranimense strains

For the first time, we report the whole genome sequence of a hydrocarbonoclastic Chryseobacterium oranimense strain isolated from Trinidad and Tobago (COTT) and its genes involved in the biotransformation of hydrocarbons and xenobiotics through functional annotation. The assembly consisted of 11 contigs with 2,794 predicted protein-coding genes which included a diverse group of gene families involved in aliphatic and polycyclic hydrocarbon degradation. Comparative genomic analyses with 18 crude-oil degrading bacteria in addition to two C. oranimense strains not associated with oil were carried out. The data revealed important differences in terms of annotated genes involved in the hydrocarbon degradation process that may explain the molecular mechanisms of hydrocarbon and xenobiotic biotransformation. Notably, many gene families were expanded to explain COTT's competitive ability to manage habitat-specific stressors. Gene-based evidence of the metabolic potential of COTT supports the application of indigenous microbes for the remediation of polluted terrestrial environments and provides a genomic resource for improving our understanding of how to optimize these characteristics for more effective bioremediation.

Natural intelligence and the 'economy' of social emotions: A connection with AI sentiment analysis

By approaching the concept of Natural Intelligence a new path may be open in a variety of theoretical and applied problems on social emotions. There is no doubt that intelligence emerges as a biological/informational phenomenon, although paradoxically a consistent elaboration of that concept has been missing. Regarding emotions, they have been keeping an unclear status, being often restricted to the anthropological or to ethological approaches closer to the behaviorist paradigm. Herein we propose a different track, centered in the life cycle advancement. The life cycle in its integrity becomes the nucleus of natural intelligence's informational processes, including the consistent expression of emotions along the maximization of fitness occasions. In human societies, the overall 'economy' of social emotions is manifest, showing up in the conspicuous interplay between bonding processes and different classes of social emotions. The essential link between natural intelligence, emotions, and the life cycle of individuals may harmonize with current progresses - and blind spots - of artificial intelligence fields such as 'sentiment analysis.'

Chromosomal gene of hybrid multisensor histidine kinase is involved in motility regulation in the rhizobacterium Azospirillum baldaniorum Sp245 under mechanical and water stress

Azospirillum alphaproteobacteria, which live in the rhizosphere of many crops, are used widely as biofertilizers. Two-component signal transduction systems (TCSs) mediate the bacterial perception of signals and the corresponding adjustment of behavior facilitating the adaptation of bacteria to their habitats. In this study, we obtained the A. baldaniorum Sp245 mutant for the AZOBR_150176 gene, which encodes the TCS of the hybrid histidine kinase/response sensory regulator (HSHK-RR). Inactivation of this gene affected bacterial morphology and motility. In mutant Sp245-HSHKΔRR-Km, the cells were still able to synthesize a functioning polar flagellum (Fla), were shorter than those of strain Sp245, and were impaired in aerotaxis, elaboration of inducible lateral flagella (Laf), and motility in semiliquid media. The mutant showed decreased transcription of the genes encoding the proteins of the secretion apparatus, which ensures the assembly of Laf, Laf flagellin, and the repressor protein of translation of the Laf flagellin's mRNA. The study examined the effects of polyethylene glycol 6000 (PEG 6000), an agent used to simulate osmotic stress and drought conditions. Under osmotic stress, the mutant was no longer able to use collective motility in semiliquid media but formed more biofilm biomass than did strain Sp245. Introduction into mutant cells of the AZOBR_150176 gene as part of an expression vector led to recovery of the lost traits, including those mediating bacterial motility under mechanical stress induced by increased medium density. The results suggest that the HSHK-RR under study modulates the response of A. baldaniorum Sp245 to mechanical and osmotic/water stress.

Gas and light: triggers of c-di-GMP-mediated regulation

The widespread bacterial second messenger c-di-GMP is responsible for regulating many important physiological functions such as biofilm formation, motility, cell differentiation, and virulence. The synthesis and degradation of c-di-GMP in bacterial cells depend, respectively, on diguanylate cyclases and c-di-GMP-specific phosphodiesterases. Since c-di-GMP metabolic enzymes (CMEs) are often fused to sensory domains, their activities are likely controlled by environmental signals, thereby altering cellular c-di-GMP levels and regulating bacterial adaptive behaviors. Previous studies on c-di-GMP-mediated regulation mainly focused on downstream signaling pathways, including the identification of CMEs, cellular c-di-GMP receptors, and c-di-GMP-regulated processes. The mechanisms of CME regulation by upstream signaling modules received less attention, resulting in a limited understanding of the c-di-GMP regulatory networks. We review here the diversity of sensory domains related to bacterial CME regulation. We specifically discuss those domains that are capable of sensing gaseous or light signals and the mechanisms they use for regulating cellular c-di-GMP levels. It is hoped that this review would help refine the complete c-di-GMP regulatory networks and improve our understanding of bacterial behaviors in changing environments. In practical terms, this may eventually provide a way to control c-di-GMP-mediated bacterial biofilm formation and pathogenesis in general.

Cloning and Functional Analysis of the VfRR17 Gene from tung tree (Vernicia fordii)

Tung tree (Vernicia fordii) is one of the four major woody oilseed species in China. However, its fruit yield is severely hampered by the low number of female flowers and the imbalanced male-to-female flower ratio, which is a problem that restricts the development of the oilseed industry. Previous research has demonstrated that the exogenous application of cytokinins can significantly augment the number of female flowers, although the underlying regulatory mechanism remains elusive. To elucidate the involvement of VfRR17, a member of the A-type ARRs family, in the exogenous cytokinin regulation of flower sexual differentiation in tung tree, this study conducted a comprehensive bioinformatic analysis of the physicochemical properties, structural characteristics, and evolutionary relationships of the protein encoded by VfRR17. Additionally, gene function analysis was performed using subcellular localization, qRT-PCR, and genetic transformation techniques. The findings revealed that the VfRR17 gene's coding region spanned 471 bp, encoding an unstable protein of 156 amino acids with a relative molecular mass of 17.4 kDa. Phylogenetic analysis demonstrated a higher similarity between VfRR17 of the tung tree and the RR17 gene of Jatropha curcas, Ricinus communis, Hevea brasiliensis, and other species within the Euphorbiaceae family compared to other species, with the greatest similarity of 86% observed with the RR17 gene of Jatropha curcas. The qRT-PCR analysis indicated that VfRR17 exhibited high expression levels during the early stage of tung tree inflorescence buds following 6-BA treatment, peaking at 24 h and displaying a 3.47-fold increase compared to that at 0 h. In female and male flowers of the tung tree, the expression in female flowers during the 1 DBF period was significantly higher than in male flowers, exhibiting a difference of approximately 47.91-fold. Furthermore, notable differential expression was observed in the root, leaf, and petiole segments of the tung tree under low-temperature stress at the 12-h time point. In transgenic Arabidopsis, the VfRR17 lines and wild-type lines exhibited significantly different flowering times under an exogenous 6-BA treatment at a concentration of 2 mg/L, with the VfRR17 lines experiencing an 11-day delay compared to the wild-type lines. Additionally, the number of fruit pods in VfRR17 transgenic Arabidopsis lines was significantly reduced by 28 compared to the wild-type lines at a 6-BA concentration of 3 mg/L. These findings suggest that VfRR17 likely plays a critical role in regulating flower development in response to exogenous 6-BA, providing valuable insights into the mechanisms underlying exogenous 6-BA-mediated regulation of female flower development in the tung tree.

The role of sensory kinase proteins in two-component signal transduction

Two-component systems (TCSs) are modular signaling circuits that regulate diverse aspects of microbial physiology in response to environmental cues. These molecular circuits comprise a sensor histidine kinase (HK) protein that contains a conserved histidine residue, and an effector response regulator (RR) protein with a conserved aspartate residue. HKs play a major role in bacterial signaling, since they perceive specific stimuli, transmit the message across the cytoplasmic membrane, and catalyze their own phosphorylation, and the trans-phosphorylation and dephosphorylation of their cognate response regulator. The molecular mechanisms by which HKs co-ordinate these functions have been extensively analyzed by genetic, biochemical, and structural approaches. Here, we describe the most common modular architectures found in bacterial HKs, and address the operation mode of the individual functional domains. Finally, we discuss the use of these signaling proteins as drug targets or as sensing devices in whole-cell biosensors with medical and biotechnological applications.

Microbial degradation of polyethylene terephthalate: a systematic review

Plastic pollution levels have increased rapidly in recent years, due to the accumulation of plastic waste, including polyethylene terephthalate (PET). Both high production and the lack of efficient methods for disposal and recycling affect diverse aquatic and terrestrial ecosystems owing to the high accumulation rates of plastics. Traditional chemical and physical degradation techniques have caused adverse effects on the environment; hence, the use of microorganisms for plastic degradation has gained importance recently. This systematic review was conducted for evaluating the reported findings about PET degradation by wild and genetically modified microorganisms to make them available for future work and to contribute to the eventual implementation of an alternative, an effective, and environmentally friendly method for the management of plastic waste such as PET. Both wild and genetically modified microorganisms with the metabolic potential to degrade this polymer were identified, in addition to the enzymes and genes used for genetic modification. The most prevalent wild-type PET-degrading microorganisms were bacteria (56.3%, 36 genera), followed by fungi (32.4%, 30 genera), microalgae (1.4%; 1 genus, namely Spirulina sp.), and invertebrate associated microbiota (2.8%). Among fungi and bacteria, the most prevalent genera were Aspergillus sp. and Bacillus sp., respectively. About genetically modified microorganisms, 50 strains of Escherichia coli, most of them expressing PETase enzyme, have been used. We emphasize the pressing need for implementing biological techniques for PET waste management on a commercial scale, using consortia of microorganisms. We present this work in five sections: an Introduction that highlights the importance of PET biodegradation as an effective and sustainable alternative, a section on Materials and methods that summarizes how the search for articles and manuscripts in different databases was done, and another Results section where we present the works found on the subject, a final part of Discussion and analysis of the literature found and finally we present a Conclusion and prospects.

Adaptation to Environmental Extremes Structures Functional Traits in Biological Soil Crust and Hypolithic Microbial Communities

Biological soil crusts (biocrusts) are widespread in drylands and deserts. At the microhabitat scale, they also host hypolithic communities that live under semitranslucent stones. Both environmental niches experience exposure to extreme conditions such as high UV radiation, desiccation, temperature fluctuations, and resource limitation. However, hypolithic communities are somewhat protected from extremes relative to biocrust communities. Conditions are otherwise similar, so comparing them can answer outstanding questions regarding adaptations to environmental extremes. Using metagenomic sequencing, we assessed the functional potential of dryland soil communities and identified the functional underpinnings of ecological niche differentiation in biocrusts versus hypoliths. We also determined the effect of the anchoring photoautotroph (moss or cyanobacteria). Genes and pathways differing in abundance between biocrusts and hypoliths indicate that biocrust communities adapt to the higher levels of UV radiation, desiccation, and temperature extremes through an increased ability to repair damaged DNA, sense and respond to environmental stimuli, and interact with other community members and the environment. Intracellular competition appears to be crucial to both communities, with biocrust communities using the Type VI Secretion System (T6SS) and hypoliths favoring a diversity of antibiotics. The dominant primary producer had a reduced effect on community functional potential compared with niche, but an abundance of genes related to monosaccharide, amino acid, and osmoprotectant uptake in moss-dominated communities indicates reliance on resources provided to heterotrophs by mosses. Our findings indicate that functional traits in dryland communities are driven by adaptations to extremes and we identify strategies that likely enable survival in dryland ecosystems. IMPORTANCE Biocrusts serve as a keystone element of desert and dryland ecosystems, stabilizing soils, retaining moisture, and serving as a carbon and nitrogen source in oligotrophic environments. Biocrusts cover approximately 12% of the Earth's terrestrial surface but are threatened by climate change and anthropogenic disturbance. Given their keystone role in ecosystem functioning, loss will have wide-spread consequences. Biocrust microbial constituents must withstand polyextreme environmental conditions including high UV exposure, desiccation, oligotrophic conditions, and temperature fluctuations over short time scales. By comparing biocrust communities with co-occurring hypolithic communities (which inhabit the ventral sides of semitranslucent stones and are buffered from environmental extremes), we identified traits that are likely key adaptations to extreme conditions. These include DNA damage repair, environmental sensing and response, and intracellular competition. Comparison of the two niches, which differ primarily in exposure levels to extreme conditions, makes this system ideal for understanding how functional traits are structured by the environment.

Genome Analysis Coupled With Transcriptomics Reveals the Reduced Fitness of a Hot Spring Cyanobacterium Mastigocladus laminosus UU774 Under Exogenous Nitrogen Supplement

The present study focuses on the stress response of a filamentous, AT-rich, heterocystous cyanobacterium Mastigocladus laminosus UU774, isolated from a hot spring, Taptapani, located in the eastern part of India. The genome of UU774 contains an indispensable fragment, scaffold_38, of unknown origin that is implicated during severe nitrogen and nutrition stress. Prolonged exposure to nitrogen compounds during starvation has profound adverse effects on UU774, leading to loss of mobility, loss of ability to fight pathogens, reduced cell division, decreased nitrogen-fixing ability, reduced ability to form biofilms, reduced photosynthetic and light-sensing ability, and reduced production of secreted effectors and chromosomal toxin genes, among others. Among genes showing extreme downregulation when grown in a medium supplemented with nitrogen with the fold change > 5 are transcriptional regulator gene WalR, carbonic anhydrases, RNA Polymerase Sigma F factor, fimbrial protein, and twitching mobility protein. The reduced expression of key enzymes involved in the uptake of phosphate and enzymes protecting oxygen-sensitive nitrogenases is significant during the presence of nitrogen. UU774 is presumed to withstand heat by overexpressing peptidases that may be degrading abnormally folded proteins produced during heat. The absence of a key gene responsible for heterocyst pattern formation, patS, and an aberrant hetN without a functional motif probably lead to the formation of a chaotic heterocyst pattern in UU774. We suggest that UU774 has diverged from Fischerella sp. PCC 9339, another hot spring species isolated in the United States.

Ancestral reconstruction of duplicated signaling proteins reveals the evolution of signaling specificity

Gene duplication is crucial to generating novel signaling pathways during evolution. However, it remains unclear how the redundant proteins produced by gene duplication ultimately acquire new interaction specificities to establish insulated paralogous signaling pathways. Here, we used ancestral sequence reconstruction to resurrect and characterize a bacterial two-component signaling system that duplicated in α-proteobacteria. We determined the interaction specificities of the signaling proteins that existed before and immediately after this duplication event and then identified key mutations responsible for establishing specificity in the two systems. Just three mutations, in only two of the four interacting proteins, were sufficient to establish specificity of the extant systems. Some of these mutations weakened interactions between paralogous systems to limit crosstalk. However, others strengthened interactions within a system, indicating that the ancestral interaction, although functional, had the potential to be strengthened. Our work suggests that protein-protein interactions with such latent potential may be highly amenable to duplication and divergence.

An Extracytoplasmic Function Sigma Factor Required for Full Virulence in Xanthomonas citri pv. citri

The genus Xanthomonas includes more than 30 phytopathogenic species that infect a wide range of plants and cause severe diseases that greatly impact crop productivity. These bacteria are highly adapted to the soil and plant environment, being found in decaying material, as epiphytes, and colonizing the plant mesophyll. Signal transduction mechanisms involved in the responses of Xanthomonas to environmental changes are still poorly characterized. Xanthomonad genomes typically encode several representatives of the extracytoplasmic function σ (σ^ECF) factors, whose physiological roles remain elusive. In this work, we functionally characterized the Xanthomonas citri pv. citri EcfL, a σ^ECF factor homologous to members of the iron-responsive FecI-like group. We show that EcfL is not required or induced during iron starvation, despite presenting the common features of other FecI-like σ^ECF factors. EcfL positively regulates one operon composed of three genes that encode a TonB-dependent receptor involved in cell surface signaling, an acid phosphatase, and a lectin-domain containing protein. Furthermore, we demonstrate that EcfL is required for full virulence in citrus, and its regulon is induced inside the plant mesophyll and in response to acid stress. Together, our study suggests a role for EcfL in the adaptation of X. citri to the plant environment, in this way contributing to its ability to cause citrus canker disease. IMPORTANCE The Xanthomonas genus comprises a large number of phytopathogenic species that infect a wide variety of economically important plants worldwide. Bacterial adaptation to the plant and soil environment relies on their repertoire of signal transduction pathways, including alternative sigma factors of the extracytoplasmic function family (σ^ECF). Here, we describe a new σ^ECF factor found in several Xanthomonas species, demonstrating its role in Xanthomonas citri virulence to citrus plants. We show that EcfL regulates a single operon containing three genes, which are also conserved in other Xanthomonas species. This study further expands our knowledge on the functions of the widespread family of σ^ECF factors in phytopathogenic bacteria.

Evolutionary Principles of Bacterial Signaling Capacity and Complexity

Microbes rely on signal transduction systems to sense and respond to environmental changes for survival and reproduction. It is generally known that niche adaptation plays an important role in shaping the signaling repertoire. However, the evolution of bacterial signaling capacity lacks systematic studies with a temporal direction. In particular, it is unclear how complexity evolved from simplicity or vice versa for signaling networks. Here, we examine the evolutionary processes of major signal transduction systems in Campylobacterota (formerly Epsilonproteobacteria), a phylum with sufficient evolutionary depth and ecological diversity. We discovered that chemosensory system increases complexity by horizontal gene transfer (HGT) of entire chemosensory classes, and different chemosensory classes rarely mix their components. Two-component system gains complexity by atypical histidine kinases fused with receiver domain to achieve multistep or branched signal transduction process. The presence and complexity of c-di-GMP-mediated system is related to the size of signaling network, and c-di-GMP pathways are easy to rewire, since enzymes and effectors can be linked without direct protein-protein interaction. Overall, signaling capacity and complexity rise and drop together in Campylobacterota, determined by sensory demand, genetic resources, and coevolution within the genomic context. These findings reflect plausible evolutionary principles for other cellular networks and genome evolution of the Bacteria domain.

Comparative Genomics of Cyclic di-GMP Metabolism and Chemosensory Pathways in Shewanella algae Strains: Novel Bacterial Sensory Domains and Functional Insights into Lifestyle Regulation

Shewanella spp. play important ecological and biogeochemical roles, due in part to their versatile metabolism and swift integration of stimuli. While Shewanella spp. are primarily considered environmental microbes, Shewanella algae is increasingly recognized as an occasional human pathogen. S. algae shares the broad metabolic and respiratory repertoire of Shewanella spp. and thrives in similar ecological niches. In S. algae, nitrate and dimethyl sulfoxide (DMSO) respiration promote biofilm formation strain specifically, with potential implication of taxis and cyclic diguanosine monophosphate (c-di-GMP) signaling. Signal transduction systems in S. algae have not been investigated. To fill these knowledge gaps, we provide here an inventory of the c-di-GMP turnover proteome and chemosensory networks of the type strain S. algae CECT 5071 and compare them with those of 41 whole-genome-sequenced clinical and environmental S. algae isolates. Besides comparative analysis of genetic content and identification of laterally transferred genes, the occurrence and topology of c-di-GMP turnover proteins and chemoreceptors were analyzed. We found S. algae strains to encode 61 to 67 c-di-GMP turnover proteins and 28 to 31 chemoreceptors, placing S. algae near the top in terms of these signaling capacities per Mbp of genome. Most c-di-GMP turnover proteins were predicted to be catalytically active; we describe in them six novel N-terminal sensory domains that appear to control their catalytic activity. Overall, our work defines the c-di-GMP and chemosensory signal transduction pathways in S. algae, contributing to a better understanding of its ecophysiology and establishing S. algae as an auspicious model for the analysis of metabolic and signaling pathways within the genus Shewanella.

IMPORTANCEShewanella spp. are widespread aquatic bacteria that include the well-studied freshwater model strain Shewanella oneidensis MR-1. In contrast, the physiology of the marine and occasionally pathogenic species Shewanella algae is poorly understood. Chemosensory and c-di-GMP signal transduction systems integrate environmental stimuli to modulate gene expression, including the switch from a planktonic to sessile lifestyle and pathogenicity. Here, we systematically dissect the c-di-GMP proteome and chemosensory pathways of the type strain S. algae CECT 5071 and 41 additional S. algae isolates. We provide insights into the activity and function of these proteins, including a description of six novel sensory domains. Our work will enable future analyses of the complex, intertwined c-di-GMP metabolism and chemotaxis networks of S. algae and their ecophysiological role.

A Large-Scale Genome-Based Survey of Acidophilic Bacteria Suggests That Genome Streamlining Is an Adaption for Life at Low pH

The genome streamlining theory suggests that reduction of microbial genome size optimizes energy utilization in stressful environments. Although this hypothesis has been explored in several cases of low-nutrient (oligotrophic) and high-temperature environments, little work has been carried out on microorganisms from low-pH environments, and what has been reported is inconclusive. In this study, we performed a large-scale comparative genomics investigation of more than 260 bacterial high-quality genome sequences of acidophiles, together with genomes of their closest phylogenetic relatives that live at circum-neutral pH. A statistically supported correlation is reported between reduction of genome size and decreasing pH that we demonstrate is due to gene loss and reduced gene sizes. This trend is independent from other genome size constraints such as temperature and G + C content. Genome streamlining in the evolution of acidophilic bacteria is thus supported by our results. The analyses of predicted Clusters of Orthologous Genes (COG) categories and subcellular location predictions indicate that acidophiles have a lower representation of genes encoding extracellular proteins, signal transduction mechanisms, and proteins with unknown function but are enriched in inner membrane proteins, chaperones, basic metabolism, and core cellular functions. Contrary to other reports for genome streamlining, there was no significant change in paralog frequencies across pH. However, a detailed analysis of COG categories revealed a higher proportion of genes in acidophiles in the following categories: "replication and repair," "amino acid transport," and "intracellular trafficking". This study brings increasing clarity regarding the genomic adaptations of acidophiles to life at low pH while putting elements, such as the reduction of average gene size, under the spotlight of streamlining theory.

The Regulatory Hierarchy Following Signal Integration by the CbrAB Two-Component System: Diversity of Responses and Functions

CbrAB is a two-component system, unique to bacteria of the family Pseudomonaceae, capable of integrating signals and involved in a multitude of physiological processes that allow bacterial adaptation to a wide variety of varying environmental conditions. This regulatory system provides a great metabolic versatility that results in excellent adaptability and metabolic optimization. The two-component system (TCS) CbrA-CbrB is on top of a hierarchical regulatory cascade and interacts with other regulatory systems at different levels, resulting in a robust output. Among the regulatory systems found at the same or lower levels of CbrAB are the NtrBC nitrogen availability adaptation system, the Crc/Hfq carbon catabolite repression cascade in Pseudomonas, or interactions with the GacSA TCS or alternative sigma ECF factor, such as SigX. The interplay between regulatory mechanisms controls a number of physiological processes that intervene in important aspects of bacterial adaptation and survival. These include the hierarchy in the use of carbon sources, virulence or resistance to antibiotics, stress response or definition of the bacterial lifestyle. The multiple actions of the CbrAB TCS result in an important competitive advantage.

The Response Regulator FlmD Regulates Biofilm Formation in Comamonas testosteroni through the Transcriptional Activator SoxR

Biofilm formation is a survival strategy by which microorganisms adapt to environmental challenges. It is regulated by various signals, such as the second messenger c-di-GMP. We previously found that the Flm chemosensory pathway could respond to chemical signals and regulate biofilm formation. This regulation is independent of c-di-GMP. A previous study revealed that the response regulator FlmD is involved in biofilm formation; however, how chemical signals are transmitted downstream of FlmD remained unclear. In the present study, transcriptome analysis and gel shift assay reveal that SoxR, a transcriptional activator of the efflux transporter acrAB-tolC operon, mediates the downstream signaling of FlmD. Phosphorylated FlmD interacts with SoxR and disrupts the interaction between SoxR and the acrAB-tolC operon. It causes a decrease in the expression of acrAB-tolC operon. The downregulation of acrA, acrB, or tolC gene expression results in making less biofilm formation. In conclusion, we identified that the transcription regulator SoxR plays a role in the c-di-GMP independent regulation of biofilm formation in Comamonas testosteroni.

Allostery and protein plasticity: the keystones for bacterial signaling and regulation

Bacteria sense intracellular and environmental signals using an array of proteins as antennas. The information is transmitted from such sensory modules to other protein domains that act as output effectors. Sensor and effector can be part of the same polypeptide or instead be separate diffusible proteins that interact specifically. The output effector modules regulate physiologic responses, allowing the cells to adapt to the varying conditions. These biological machineries are known as signal transduction systems (STSs). Despite the captivating architectural diversity exhibited by STS proteins, a universal feature is their allosteric regulation: signal binding at one site modifies the activity at a physically distant site. Allostery requires protein plasticity, precisely encoded within their 3D structures, and implicating programmed molecular motions. This review summarizes how STS proteins connect stimuli to specific responses by exploiting allostery and protein plasticity. Illustrative examples spanning a wide variety of protein folds will focus on one- and two-component systems (TCSs). The former encompass the entire transmission route within a single polypeptide, whereas TCSs have evolved as separate diffusible proteins that interact specifically, sometimes including additional intermediary proteins in the pathway. Irrespective of their structural diversity, STS proteins are able to modulate their own molecular motions, which can be relatively slow, rigid-body movements, all the way to fast fluctuations in the form of macromolecular flexibility, thus spanning a continuous protein dynamics spectrum. In sum, STSs rely on allostery to steer information transmission, going from simple two-state switching to rich multi-state conformational order/disorder transitions.

The Signaling Pathway That cGAMP Riboswitches Found: Analysis and Application of Riboswitches to Study cGAMP Signaling in Geobacter sulfurreducens

The Hypr cGAMP signaling pathway was discovered via the function of the riboswitch. In this study, we show the development of a method for affinity capture followed by sequencing to identify non-coding RNA regions that bind nucleotide signals such as cGAMP. The RNAseq of affinity-captured cGAMP riboswitches from the Geobacter sulfurreducens transcriptome highlights general challenges that remain for this technique. Furthermore, by applying riboswitch reporters in vivo, we identify new growth conditions and transposon mutations that affect cGAMP levels in G. sulfurreducens. This work reveals an extensive regulatory network and supports a second functional cGAMP synthase gene in G. sulfurreducens. The activity of the second synthase was validated using riboswitch-based fluorescent biosensors, and is the first known example of an active enzyme with a variant GGDDF motif.

A core and pan gene map of Leptospira genus and its interactions with human host

Leptospira species are the etiological agent of an emerging zoonotic disease known as "Leptospirosis" that substantially affects both human health and economy across the globe. Despite the global importance of the disease, pathogenetic features, host-adaptation and proper diagnosis of this bacteria remains lacking. To accomplish these gaps, pan-genome of Leptospira genus was explored in the present study. The pan-genome of Leptospira genus was comprised of core (692) and accessory parts (softcore:1804, shell:6432, cloud:16,600). The functional analysis revealed the abundancy of "Translation, ribosomal structure and biogenesis" COG class in core-genes; whereas in accessory parts, genes involved in signal transduction was the most abundant. Furthermore, pathogen-host interaction (PHI) analysis of core and accessory proteins with human proteins showed the presence of a total of 599 and 510 interactions, respectively. There were eight hubs in core PHI network and five hubs in PHI network of accessory proteins. The human's proteins involved in these interactions were found functionally enriched in metabolic processes, responses to stimulus and immune system processes. Further, pan-genome based phylogeny separated the Leptospira genus in three major clades (belonging to P1, P2 and S) which relates with their pathogenicity level. Additionally, pathogenic and saprophytic clade specific genes of Leptospira have also been identified and functionally annotated for COG, KEGG and virulence factors. The results revealed the presence of 102 pathogenic and 215 saprophytic group specific gene clusters. The COG functional annotation of pathogen specific genes showed that defence mechanism followed by signal transduction mechanisms category were most significantly enriched COG categories; whereas in saprophytic group, signal transduction mechanisms was the most abundant COG, suggesting their role in adaptation and hence important for microbe's evolution and survival. In conclusion, this study provides a new insight of genomic features of Leptospira genus which may further be implemented for development of better control actions of the disease.

From Molecular Recognition to the "Vehicles" of Evolutionary Complexity: An Informational Approach

Countless informational proposals and models have explored the singular characteristics of biological systems: from the initial choice of information terms in the early days of molecular biology to the current bioinformatic avalanche in this “omic” era. However, this was conducted, most often, within partial, specialized scopes or just metaphorically. In this paper, we attempt a consistent informational discourse, initially based on the molecular recognition paradigm, which addresses the main stages of biological organization in a new way. It considers the interconnection between signaling systems and information flows, between informational architectures and biomolecular codes, between controlled cell cycles and multicellular complexity. It also addresses, in a new way, a central issue: how new evolutionary paths are opened by the cumulated action of multiple variation engines or mutational ‘vehicles’ evolved for the genomic exploration of DNA sequence space. Rather than discussing the possible replacement, extension, or maintenance of traditional neo-Darwinian tenets, a genuine informational approach to evolutionary phenomena is advocated, in which systemic variation in the informational architectures may induce differential survival (self-construction, self-maintenance, and reproduction) of biological agents within their open ended environment.

Exploring the expression and functionality of the rsm sRNAs in Pseudomonas syringae pv. tomato DC3000

The Gac-rsm pathway is a global regulatory network that governs mayor lifestyle and metabolic changes in gamma-proteobacteria. In a previous study, we uncovered the role of CsrA proteins promoting growth and repressing motility, alginate production and virulence in the model phytopathogen Pseudomonas syringae pv. tomato (Pto) DC3000. Here, we focus on the expression and regulation of the rsm regulatory sRNAs, since Pto DC3000 exceptionally has seven variants (rsmX1-5, rsmY and rsmZ). The presented results offer further insights into the functioning of the complex Gac-rsm pathway and the interplay among its components. Overall, rsm expressions reach maximum levels at high cell densities, are unaffected by surface detection, and require GacA for full expression. The rsm levels of expression and GacA-dependence are determined by the sequences found in their -35/-10 promoter regions and GacA binding boxes, respectively. rsmX5 stands out for being the only rsm in Pto DC3000 whose high expression does not require GacA, constituting the main component of the total rsm pool in a gacA mutant. The deletion of rsmY and rsmZ had minor effects on Pto DC3000 motility and virulence phenotypes, indicating that rsmX1-5 can functionally replace them. On the other hand, rsmY or rsmZ overexpression in a gacA mutant did not revert its phenotype. Additionally, a negative feedback regulatory loop in which the CsrA3 protein promotes its own titration by increasing the levels of several rsm RNAs in a GacA-dependent manner has been disclosed as part of this work.

Towards the Idea of Molecular Brains

How can single cells without nervous systems perform complex behaviours such as habituation, associative learning and decision making, which are considered the hallmark of animals with a brain? Are there molecular systems that underlie cognitive properties equivalent to those of the brain? This review follows the development of the idea of molecular brains from Darwin’s “root brain hypothesis”, through bacterial chemotaxis, to the recent discovery of neuron-like r-protein networks in the ribosome. By combining a structural biology view with a Bayesian brain approach, this review explores the evolutionary labyrinth of information processing systems across scales. Ribosomal protein networks open a window into what were probably the earliest signalling systems to emerge before the radiation of the three kingdoms. While ribosomal networks are characterised by long-lasting interactions between their protein nodes, cell signalling networks are essentially based on transient interactions. As a corollary, while signals propagated in persistent networks may be ephemeral, networks whose interactions are transient constrain signals diffusing into the cytoplasm to be durable in time, such as post-translational modifications of proteins or second messenger synthesis. The duration and nature of the signals, in turn, implies different mechanisms for the integration of multiple signals and decision making. Evolution then reinvented networks with persistent interactions with the development of nervous systems in metazoans. Ribosomal protein networks and simple nervous systems display architectural and functional analogies whose comparison could suggest scale invariance in information processing. At the molecular level, the significant complexification of eukaryotic ribosomal protein networks is associated with a burst in the acquisition of new conserved aromatic amino acids. Knowing that aromatic residues play a critical role in allosteric receptors and channels, this observation suggests a general role of π systems and their interactions with charged amino acids in multiple signal integration and information processing. We think that these findings may provide the molecular basis for designing future computers with organic processors.

Bioluminescence and Photoreception in Unicellular Organisms: Light-Signalling in a Bio-Communication Perspective

Bioluminescence, the emission of light catalysed by luciferases, has evolved in many taxa from bacteria to vertebrates and is predominant in the marine environment. It is now well established that in animals possessing a nervous system capable of integrating light stimuli, bioluminescence triggers various behavioural responses and plays a role in intra- or interspecific visual communication. The function of light emission in unicellular organisms is less clear and it is currently thought that it has evolved in an ecological framework, to be perceived by visual animals. For example, while it is thought that bioluminescence allows bacteria to be ingested by zooplankton or fish, providing them with favourable conditions for growth and dispersal, the luminous flashes emitted by dinoflagellates may have evolved as an anti-predation system against copepods. In this short review, we re-examine this paradigm in light of recent findings in microorganism photoreception, signal integration and complex behaviours. Numerous studies show that on the one hand, bacteria and protists, whether autotrophs or heterotrophs, possess a variety of photoreceptors capable of perceiving and integrating light stimuli of different wavelengths. Single-cell light-perception produces responses ranging from phototaxis to more complex behaviours. On the other hand, there is growing evidence that unicellular prokaryotes and eukaryotes can perform complex tasks ranging from habituation and decision-making to associative learning, despite lacking a nervous system. Here, we focus our analysis on two taxa, bacteria and dinoflagellates, whose bioluminescence is well studied. We propose the hypothesis that similar to visual animals, the interplay between light-emission and reception could play multiple roles in intra- and interspecific communication and participate in complex behaviour in the unicellular world.

PdeA is required for the rod shape morphology of Brucella abortus

Cyclic-di-GMP plays crucial role in the cell cycle regulation of the α-Proteobacterium Caulobacter crescentus. Here we investigated its role in the α-Proteobacterium Brucella abortus, a zoonotic intracellular pathogen. Surprisingly, deletion of all predicted cyclic-di-GMP synthesizing or degrading enzymes did not drastically impair the growth of B. abortus, nor its ability to grow inside cell lines. As other Rhizobiales, B. abortus displays unipolar growth from the new cell pole generated by cell division. We found that the phosphodiesterase PdeA, the ortholog of the essential polar growth factor RgsP of the Rhizobiale Sinorhizobium meliloti, is required for rod shape integrity but is not essential for B. abortus growth. Indeed, the radius of the pole is increased by 31 ± 1.7% in a ΔpdeA mutant, generating a coccoid morphology. A mutation in the cyclic-di-GMP phosphodiesterase catalytic site of PdeA does not generate the coccoid morphology and the ΔpdeA mutant kept the ability to recruit markers of new and old poles. However, the presence of PdeA is required in an intra-nasal mouse model of infection. In conclusion, we propose that PdeA contributes to bacterial morphology and virulence in B. abortus, but it is not crucial for polarity and asymmetric growth.

Complete genome sequence and identification of polyunsaturated fatty acid biosynthesis genes of the myxobacterium Minicystis rosea DSM 24000T

Background

Myxobacteria harbor numerous biosynthetic gene clusters that can produce a diverse range of secondary metabolites. Minicystis rosea DSM 24000^T is a soil-dwelling myxobacterium belonging to the suborderSorangiineae and family Polyangiaceae and is known to produce various secondary metabolites as well as polyunsaturated fatty acids (PUFAs). Here, we use whole-genome sequencing to explore the diversity of biosynthetic gene clusters in M. rosea.

Results

Using PacBio sequencing technology, we assembled the 16.04 Mbp complete genome of M. rosea DSM 24000^T, the largest bacterial genome sequenced to date. About 44% of its coding potential represents paralogous genes predominantly associated with signal transduction, transcriptional regulation, and protein folding. These genes are involved in various essential functions such as cellular organization, diverse niche adaptation, and bacterial cooperation, and enable social behavior like gliding motility, sporulation, and predation, typical of myxobacteria. A profusion of eukaryotic-like kinases (353) and an elevated ratio of phosphatases (8.2/1) in M. rosea as compared to other myxobacteria suggest gene duplication as one of the primary modes of genome expansion. About 7.7% of the genes are involved in the biosynthesis of a diverse array of secondary metabolites such as polyketides, terpenes, and bacteriocins. Phylogeny of the genes involved in PUFA biosynthesis (pfa) together with the conserved synteny of the complete pfa gene cluster suggests acquisition via horizontal gene transfer from Actinobacteria.

Conclusion

Overall, this study describes the complete genome sequence of M. rosea, comparative genomic analysis to explore the putative reasons for its large genome size, and explores the secondary metabolite potential, including the biosynthesis of polyunsaturated fatty acids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07955-x.

Spatial organization enhances versatility and specificity in cyclic di-GMP signaling

The second messenger cyclic di-GMP regulates a variety of processes in bacteria, many of which are centered around the decision whether to adopt a sessile or a motile life style. Regulatory circuits include pathogenicity, biofilm formation, and motility in a wide variety of bacteria, and play a key role in cell cycle progression in Caulobacter crescentus. Interestingly, multiple, seemingly independent c-di-GMP pathways have been found in several species, where deletions of individual c-di-GMP synthetases (DGCs) or hydrolases (PDEs) have resulted in distinct phenotypes that would not be expected based on a freely diffusible second messenger. Several recent studies have shown that individual signaling nodes exist, and additionally, that protein/protein interactions between DGCs, PDEs and c-di-GMP receptors play an important role in signaling specificity. Additionally, subcellular clustering has been shown to be employed by bacteria to likely generate local signaling of second messenger, and/or to increase signaling specificity. This review highlights recent findings that reveal how bacteria employ spatial cues to increase the versatility of second messenger signaling.

Cyclic di-GMP signaling controlling the free-living lifestyle of alpha-proteobacterial rhizobia

Cyclic-di-GMP (c-di-GMP) is a ubiquitous bacterial second messenger which has been associated with a motile to sessile lifestyle switch in many bacteria. Here, we review recent insights into c-di-GMP regulated processes related to environmental adaptations in alphaproteobacterial rhizobia, which are diazotrophic bacteria capable of fixing nitrogen in symbiosis with their leguminous host plants. The review centers on Sinorhizobium meliloti, which in the recent years was intensively studied for its c-di-GMP regulatory network.

Nitrate- and Nitrite-Sensing Histidine Kinases: Function, Structure, and Natural Diversity

Under anaerobic conditions, bacteria may utilize nitrates and nitrites as electron acceptors. Sensitivity to nitrous compounds is achieved via several mechanisms, some of which rely on sensor histidine kinases (HKs). The best studied nitrate- and nitrite-sensing HKs (NSHKs) are NarQ and NarX from Escherichia coli. Here, we review the function of NSHKs, analyze their natural diversity, and describe the available structural information. In particular, we show that around 6000 different NSHK sequences forming several distinct clusters may now be found in genomic databases, comprising mostly the genes from Beta- and Gammaproteobacteria as well as from Bacteroidetes and Chloroflexi, including those from anaerobic ammonia oxidation (annamox) communities. We show that the architecture of NSHKs is mostly conserved, although proteins from Bacteroidetes lack the HAMP and GAF-like domains yet sometimes have PAS. We reconcile the variation of NSHK sequences with atomistic models and pinpoint the structural elements important for signal transduction from the sensor domain to the catalytic module over the transmembrane and cytoplasmic regions spanning more than 200 Å.

Functional trait relationships demonstrate life strategies in terrestrial prokaryotes

Functional, physiological traits are the underlying drivers of niche differentiation. A common framework related to niches occupied by terrestrial prokaryotes is based on copiotrophy or oligotrophy, where resource investment is primarily in either rapid growth or stress tolerance, respectively. A quantitative trait-based approach sought relationships between taxa, traits and niche in terrestrial prokaryotes. With 175 taxa from 11 Phyla and 35 Families (n = 5 per Family), traits were considered as discrete counts of shared genome-encoded proteins. Trait composition strongly supported non-random functional distributions as preferential clustering of related taxa via unweighted pair-group method with arithmetic mean. Trait similarity between taxa increased as taxonomic rank decreased. A suite of Random Forest models identified traits significantly enriched or depleted in taxonomic groups. These traits conveyed functions related to rapid growth, nutrient acquisition and stress tolerance consistent with their presence in copiotroph-oligotroph niches. Hierarchical clustering of traits identified a clade of competitive, copiotrophic Families resilient to oxidative stress versus glycosyltransferase-enriched oligotrophic Families resistant to antimicrobials and environmental stress. However, the formation of five clades suggested a more nuanced view to describe niche differentiation in terrestrial systems is necessary. We suggest considering traits involved in both resource investment and acquisition when predicting niche.

Genomic and molecular evolutionary dynamics of transcriptional response regulator genes in bacterial species of the Harveyi clade of Vibrio

Transcriptional response regulators (TRR) are the most abundant signal transducers in prokaryotic systems that mediate intracellular changes in response to environmental signals. They are involved in a wide range of biological processes that allow bacteria to persist in particular habitats. There is strong evidence that the bacterial habitat and their lifestyle influence the size of their TRR genetic repertoire. Therefore, it would be expected that the evolution of bacterial genomes could be linked to natural selection processes. To test this hypothesis, we explored the evolutionary dynamics of TRR genes of the widely studied Harveyi clade of the genus Vibrio at the molecular and genomic levels. Our results suggest that the TRR genetic repertoire of the species belonging to the Harveyi clade is a product of genomic reduction and expansion. The gene loss and gains that drive their genomic reduction and expansion could be attributed to natural selection and random genetic drift. It seems that natural selection acts to maintain the ancestral state of core TRR genes (shared by all species) by purifying processes and could be driving the loss of some accessory (found in certain species) genes through the diversification of sequences. The neutrality observed in gene gain could be attributed to spontaneous events as horizontal gene transfer driven by stochastic events as occurs in random genetic drift.

Novel Two-Component System-Like Elements Reveal Functional Domains Associated with Restriction-Modification Systems and paraMORC ATPases in Bacteria

Two-component systems (TCS) are important types of machinery allowing for efficient signal recognition and transmission in bacterial cells. The majority of TCSs utilized by bacteria is composed of a sensor histidine kinase (HK) and a cognate response regulator (RR). In the present study, we report two newly predicted protein domains—both to be included in the next release of the Pfam database: Response_reg_2 (PF19192) and HEF_HK (PF19191)—in bacteria which exhibit high structural similarity, respectively, with typical domains of RRs and HKs. Additionally, the genes encoding for the novel predicted domains exhibit a 91.6% linkage observed across 644 genomic regions recovered from 628 different bacterial strains. The remarkable adjacent colocalization between genes carrying Response_reg_2 and HEF_HK in addition to their conserved structural features, which are highly similar to those from well-known HKs and RRs, raises the possibility of Response_reg_2 and HEF_HK constituting a new TCS in bacteria. The genomic regions in which these predicted two-component systems-like are located additionally exhibit an overrepresented presence of restriction–modification (R–M) systems especially the type II R–M. Among these, there is a conspicuous presence of C-5 cytosine-specific DNA methylases which may indicate a functional association with the newly discovered domains. The solid presence of R–M systems and the presence of the GHKL family domain HATPase_c_3 across most of the HEF_HK-containing genes are also indicative that these genes are evolutionarily related to the paraMORC family of ATPases.

The novel PII-interactor PirC identifies phosphoglycerate mutase as key control point of carbon storage metabolism in cyanobacteria

Nitrogen limitation imposes a major transition in the lifestyle of nondiazotrophic cyanobacteria that is controlled by a complex interplay of regulatory factors involving the pervasive signal processor PII Immediately upon nitrogen limitation, newly fixed carbon is redirected toward glycogen synthesis. How the metabolic switch for diverting fixed carbon toward the synthesis of glycogen or of cellular building blocks is operated was so far poorly understood. Here, using the nondiazotrophic cyanobacterium Synechocystis sp. PCC 6803 as model system, we identified a novel PII interactor, the product of the sll0944 gene, which we named PirC. We show that PirC binds to and inhibits the activity of 2,3-phosphoglycerate-independent phosphoglycerate mutase (PGAM), the enzyme that deviates newly fixed CO2 toward lower glycolysis. The binding of PirC to either PII or PGAM is tuned by the metabolite 2-oxoglutarate (2-OG), which accumulates upon nitrogen starvation. In these conditions, the high levels of 2-OG dissociate the PirC-PII complex to promote PirC binding to and inhibition of PGAM. Accordingly, a PirC-deficient mutant showed strongly reduced glycogen levels upon nitrogen deprivation, whereas polyhydroxybutyrate granules were overaccumulated compared to wild-type. Metabolome analysis revealed an imbalance in 3-phosphoglycerate to pyruvate levels in the pirC mutant, confirming that PirC controls the carbon flux in cyanobacteria via mutually exclusive interaction with either PII or PGAM.

Pangenome Analytics Reveal Two-Component Systems as Conserved Targets in ESKAPEE Pathogens

The ESKAPEE pathogens are the leading cause of health care-associated infections worldwide. Two-component systems (TCSs) can be used as effective targets against pathogenic bacteria since they are ubiquitous and manage various vital functions such as antibiotic resistance, virulence, biofilms, quorum sensing, and pH balance, among others.

The two-component system (TCS) helps bacteria sense and respond to environmental stimuli through histidine kinases and response regulators. TCSs are the largest family of multistep signal transduction processes, and they are involved in many important cellular processes such as antibiotic resistance, pathogenicity, quorum sensing, osmotic stress, and biofilms. Here, we perform the first comprehensive study to highlight the role of TCSs as potential drug targets against ESKAPEE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp., and Escherichia coli) pathogens through annotation, mapping, pangenomic status, gene orientation, and sequence variation analysis. The distribution of the TCSs is group specific with regard to Gram-positive and Gram-negative bacteria, except for KdpDE. The TCSs among ESKAPEE pathogens form closed pangenomes, except for Pseudomonas aeruginosa. Furthermore, their conserved nature due to closed pangenomes might make them good drug targets. Fitness score analysis suggests that any mutation in some TCSs such as BaeSR, ArcBA, EvgSA, and AtoSC, etc., might be lethal to the cell. Taken together, the results of this pangenomic assessment of TCSs reveal a range of strategies deployed by the ESKAPEE pathogens to manifest pathogenicity and antibiotic resistance. This study further suggests that the conserved features of TCSs might make them an attractive group of potential targets with which to address antibiotic resistance.

IMPORTANCE The ESKAPEE pathogens are the leading cause of health care-associated infections worldwide. Two-component systems (TCSs) can be used as effective targets against pathogenic bacteria since they are ubiquitous and manage various vital functions such as antibiotic resistance, virulence, biofilms, quorum sensing, and pH balance, among others. This study provides a comprehensive overview of the pangenomic status of the TCSs among ESKAPEE pathogens. The annotation and pangenomic analysis of TCSs show that they are significantly distributed and conserved among the pathogens, as most of them form closed pangenomes. Furthermore, our analysis also reveals that the removal of the TCSs significantly affects the fitness of the cell. Hence, they may be used as promising drug targets against bacteria.

The Journey from Two-Step to Multi-Step Phosphorelay Signaling Systems

BACKGROUND

The two-component signaling (TCS) system is an important signal transduction machinery in prokaryotes and eukaryotes, excluding animals, that uses a protein phosphorylation mechanism for signal transmission.

CONCLUSION

Prokaryotes have a primitive type of TCS machinery, which mainly comprises a membrane-bound sensory histidine kinase (HK) and its cognate cytoplasmic response regulator (RR). Hence, it is sometimes referred to as two-step phosphorelay (TSP). Eukaryotes have more sophisticated signaling machinery, with an extra component - a histidine-containing phosphotransfer (HPT) protein that shuttles between HK and RR to communicate signal baggage. As a result, the TSP has evolved from a two-step phosphorelay (His-Asp) in simple prokaryotes to a multi-step phosphorelay (MSP) cascade (His-Asp-His-Asp) in complex eukaryotic organisms, such as plants, to mediate the signaling network. This molecular evolution is also reflected in the form of considerable structural modifications in the domain architecture of the individual components of the TCS system. In this review, we present TCS system's evolutionary journey from the primitive TSP to advanced MSP type across the genera. This information will be highly useful in designing the future strategies of crop improvement based on the individual members of the TCS machinery.

Signal transduction schemes in Pseudomonas syringae

To cope with their continually fluctuating surroundings, pathovars of the unicellular phytopathogen Pseudomonas syringae have developed rapid and sophisticated signalling networks to sense extracellular stimuli, which allow them to adjust their cellular composition to survive and cause diseases in host plants. Comparative genomic analyses of P. syringae strains have identified various genes that encode several classes of signalling proteins, although how this bacterium directly perceives these environmental cues remains elusive. Recent work has revealed new mechanisms of a cluster of bacterial signal transduction systems that mainly include two-component systems (such as RhpRS, GacAS, CvsRS and AauRS), extracytoplasmic function sigma factors (such as HrpL and AlgU), nucleotide-based secondary messengers, methyl-accepting chemotaxis sensor proteins and several other intracellular surveillance systems. In this review, we compile a list of the signal transduction mechanisms that P. syringae uses to monitor and respond in a timely manner to intracellular and external conditions. Further understanding of these surveillance processes will provide new perspectives from which to combat P. syringae infections.

Searching Hit Potential Antimicrobials in Natural Compounds Space against Biofilm Formation

Biofilms are communities of microorganisms that can colonize biotic and abiotic surfaces and thus play a significant role in the persistence of bacterial infection and resistance to antimicrobial. About 65% and 80% of microbial and chronic infections are associated with biofilm formation, respectively. The increase in infections by multi-resistant bacteria instigates the need for the discovery of novel natural-based drugs that act as inhibitory molecules. The inhibition of diguanylate cyclases (DGCs), the enzyme implicated in the synthesis of the second messenger, cyclic diguanylate (c-di-GMP), involved in the biofilm formation, represents a potential approach for preventing the biofilm development. It has been extensively studied using PleD protein as a model of DGC for in silico studies as virtual screening and as a model for in vitro studies in biofilms formation. This study aimed to search for natural products capable of inhibiting the Caulobacter crescentus enzyme PleD. For this purpose, 224,205 molecules from the natural products ZINC15 database, have been evaluated through molecular docking and molecular dynamic simulation. Our results suggest trans-Aconitic acid (TAA) as a possible starting point for hit-to-lead methodologies to obtain new inhibitors of the PleD protein and hence blocking the biofilm formation.

Computation in bacterial communities

Bacteria across many scales are involved in a dynamic process of information exchange to coordinate activity and community structure within large and diverse populations. The molecular components bacteria use to communicate have been discovered and characterized, and recent efforts have begun to understand the potential for bacterial signal exchange to gather information from the environment and coordinate collective behaviors. Such computations made by bacteria to coordinate the action of a population of cells in response to information gathered by a multitude of inputs is a form of collective intelligence. These computations must be robust to fluctuations in both biological, chemical, and physical parameters as well as to operate with energetic efficiency. Given these constraints, what are the limits of computation by bacterial populations and what strategies have evolved to ensure bacterial communities efficiently work together? Here the current understanding of information exchange and collective decision making that occur in microbial populations will be reviewed. Looking toward the future, we consider how a deeper understanding of bacterial computation will inform future direction in microbiology, biotechnology, and biophysics.

Complete genome sequence of fish-pathogenic Aeromonas hydrophila HX-3 and a comparative analysis: insights into virulence factors and quorum sensing

The gram-negative, aerobic, rod-shaped bacterium Aeromonas hydrophila, the causative agent of motile aeromonad septicaemia, has attracted increasing attention due to its high pathogenicity. Here, we constructed the complete genome sequence of a virulent strain, A. hydrophila HX-3 isolated from Pseudosciaena crocea and performed comparative genomics to investigate its virulence factors and quorum sensing features in comparison with those of other Aeromonas isolates. HX-3 has a circular chromosome of 4,941,513 bp with a 61.0% G + C content encoding 4483 genes, including 4318 protein-coding genes, and 31 rRNA, 127 tRNA and 7 ncRNA operons. Seventy interspersed repeat and 153 tandem repeat sequences, 7 transposons, 8 clustered regularly interspaced short palindromic repeats, and 39 genomic islands were predicted in the A. hydrophila HX-3 genome. Phylogeny and pan-genome were also analyzed herein to confirm the evolutionary relationships on the basis of comparisons with other fully sequenced Aeromonas genomes. In addition, the assembled HX-3 genome was successfully annotated against the Cluster of Orthologous Groups of proteins database (76.03%), Gene Ontology database (18.13%), and Kyoto Encyclopedia of Genes and Genome pathway database (59.68%). Two-component regulatory systems in the HX-3 genome and virulence factors profiles through comparative analysis were predicted, providing insights into pathogenicity. A large number of genes related to the AHL-type 1 (ahyI, ahyR), LuxS-type 2 (luxS, pfs, metEHK, litR, luxOQU) and QseBC-type 3 (qseB, qseC) autoinducer systems were also identified. As a result of the expression of the ahyI gene in Escherichia coli BL21 (DE3), combined UPLC-MS/MS profiling led to the identification of several new N-acyl-homoserine lactone compounds synthesized by AhyI. This genomic analysis determined the comprehensive QS systems of A. hydrophila, which might provide novel information regarding the mechanisms of virulence signatures correlated with QS.

Carbon/nitrogen homeostasis control in cyanobacteria

Carbon/nitrogen (C/N) balance sensing is a key requirement for the maintenance of cellular homeostasis. Therefore, cyanobacteria have evolved a sophisticated signal transduction network targeting the metabolite 2-oxoglutarate (2-OG), the carbon skeleton for nitrogen assimilation. It serves as a status reporter for the cellular C/N balance that is sensed by transcription factors NtcA and NdhR and the versatile PII-signaling protein. The PII protein acts as a multitasking signal-integrating regulator, combining the 2-OG signal with the energy state of the cell through adenyl-nucleotide binding. Depending on these integrated signals, PII orchestrates metabolic activities in response to environmental changes through binding to various targets. In addition to 2-OG, other status reporter metabolites have recently been discovered, mainly indicating the carbon status of the cells. One of them is cAMP, which is sensed by the PII-like protein SbtB. The present review focuses, with a main emphasis on unicellular model strains Synechoccus elongatus and Synechocystis sp. PCC 6803, on the physiological framework of these complex regulatory loops, the tight linkage to metabolism and the molecular mechanisms governing the signaling processes.

Systematic Reconstruction of the Complete Two-Component Sensorial Network in Staphylococcus aureus

Bacteria are able to sense environmental conditions and respond accordingly. Their sensorial system relies on pairs of sensory and regulatory proteins, known as two-component systems (TCSs). The majority of bacteria contain dozens of TCSs, each of them responsible for sensing and responding to a different range of signals. Traditionally, the function of each TCS has been determined by analyzing the changes in gene expression caused by the absence of individual TCSs. Here, we used a bacterial strain deprived of the complete TC sensorial system to introduce, one by one, the active form of every TCS. This gain-of-function strategy allowed us to identify the changes in gene expression conferred by each TCS without interference of other members of the family.

In bacteria, adaptation to changes in the environment is mainly controlled through two-component signal transduction systems (TCSs). Most bacteria contain dozens of TCSs, each of them responsible for sensing a different range of signals and controlling the expression of a repertoire of target genes (regulon). Over the years, identification of the regulon controlled by each individual TCS in different bacteria has been a recurrent question. However, limitations associated with the classical approaches used have left our knowledge far from complete. In this report, using a pioneering approach in which a strain devoid of the complete nonessential TCS network was systematically complemented with the constitutively active form of each response regulator, we have reconstituted the regulon of each TCS of S. aureus in the absence of interference between members of the family. Transcriptome sequencing (RNA-Seq) and proteomics allowed us to determine the size, complexity, and insulation of each regulon and to identify the genes regulated exclusively by one or many TCSs. This gain-of-function strategy provides the first description of the complete TCS regulon in a living cell, which we expect will be useful to understand the pathobiology of this important pathogen.

IMPORTANCE Bacteria are able to sense environmental conditions and respond accordingly. Their sensorial system relies on pairs of sensory and regulatory proteins, known as two-component systems (TCSs). The majority of bacteria contain dozens of TCSs, each of them responsible for sensing and responding to a different range of signals. Traditionally, the function of each TCS has been determined by analyzing the changes in gene expression caused by the absence of individual TCSs. Here, we used a bacterial strain deprived of the complete TC sensorial system to introduce, one by one, the active form of every TCS. This gain-of-function strategy allowed us to identify the changes in gene expression conferred by each TCS without interference of other members of the family.

Sensing, Signaling, and Secretion: A Review and Analysis of Systems for Regulating Host Interaction in Wolbachia

Wolbachia (Anaplasmataceae) is an endosymbiont of arthropods and nematodes that resides within host cells and is well known for manipulating host biology to facilitate transmission via the female germline. The effects Wolbachia has on host physiology, combined with reproductive manipulations, make this bacterium a promising candidate for use in biological- and vector-control. While it is becoming increasingly clear that Wolbachia's effects on host biology are numerous and vary according to the host and the environment, we know very little about the molecular mechanisms behind Wolbachia's interactions with its host. Here, I analyze 29 Wolbachia genomes for the presence of systems that are likely central to the ability of Wolbachia to respond to and interface with its host, including proteins for sensing, signaling, gene regulation, and secretion. Second, I review conditions under which Wolbachia alters gene expression in response to changes in its environment and discuss other instances where we might hypothesize Wolbachia to regulate gene expression. Findings will direct mechanistic investigations into gene regulation and host-interaction that will deepen our understanding of intracellular infections and enhance applied management efforts that leverage Wolbachia.