Klebsiella variicola and Klebsiella quasipneumoniae with capacity to adapt to clinical and plant settings

Pathogen Profile of Klebsiella variicola, the Causative Agent of Banana Sheath Rot

Banana (Musa spp.) is an important fruit and food crop worldwide. In recent years, banana sheath rot has become a major problem in banana cultivation, causing plant death and substantial economic losses. Nevertheless, the pathogen profile of this disease has not been fully characterized. Klebsiella variicola is a versatile bacterium capable of colonizing different hosts, such as plants, humans, insects, and animals, and is recognized as an emerging pathogen in various hosts. In this study, we obtained 12 bacterial isolates from 12 different banana samples showing banana sheath rot in Guangdong and Guangxi Provinces, China. Phylogenetic analysis based on 16S rRNA sequences confirmed that all 12 isolates were K. variicola strains. We sequenced the genomes of these strains, performed comparative genomic analysis with other sequenced K. variicola strains, and found a lack of consistency in accessory gene content among these K. variicola strains. However, prediction based on the pan-genome of K. variicola revealed 22 unique virulence factors carried by the 12 pathogenic K. variicola isolates. Microbiome and microbial interaction network analysis of endophytes between the healthy tissues of diseased plants and healthy plants of two cultivars showed that Methanobacterium negatively interacts with Klebsiella in banana plants and that Herbaspirillum might indirectly inhibit Methanobacterium to promote Klebsiella growth. These results suggest that banana sheath rot is caused by the imbalance of plant endophytes and opportunistic pathogenic bacteria, providing an important basis for research and control of this disease.[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Molecular insights into novel environmental strains of Klebsiella quasipneumoniae harboring different antimicrobial-resistance genes

Introduction

The emergence of bacterial pathogens in environmental hosts represents a major risk to public health. This study aimed at characterizing seven novel environmental strains of K. quasipneumoniae using a genomic approach which was misidentified by phenotypic methods in a previous batch of 27 species thought to be K. pneumoniae.

Methods

Whole-genome sequencing was performed using the Illumina platform, and the generated raw reads were de novo assembled. Comparative genomic, resistome, virulome, mobilome, and phylogeny were then investigated using dierent bioinformatics tools.

Results

Six strains were identified as K. quasipneumoniae subsp similipneumoniae and one as K. quasipneumoniae subsp. quasipneumoniae. All isolates were resistant to ampicillin, cephalexin, and amoxicillin-clavulanic acid and harbored the fosA, bla _OKP types, oqxB, and oqxA genes. One isolate additionally harbored a gene cassettes consisting of bla _SHV-1, bla _OXA-1, aac(6')-Ib-cr, catB genes. The aminoglycoside-modifying enzyme gene aph(3")-Ia was bracketed by two insertion elements. Plasmid analyses showed that IncFIB_K was the most prevalent plasmid, circulating in six isolates, while one isolate exhibited seven different plasmids. The isolates have virulence genes responsible for capsule formation, lipopolysaccharide, iron uptake aerobactin (iutA), salmochelins (iroE, iroN), enterobactin siderophore, adherence, and biofilm formation (mrkA, mrkB, mrkC, mrkD, mrkF, and mrkH).

Conclusion

Our study highlights the ecology and transmission of K. quasipneumoniae (which have the ability to disseminate to other environmental sources including animals) outside the clinical setting and the contribution of water, vegetables, and table surfaces as potential reservoirs of farm-to-fork transmission of disease via local markets in Khartoum, Sudan.

Analysis of a novel class A β-lactamase OKP-B-6 of Klebsiella quasipneumoniae: structural characterisation and interaction with commercially available drugs

BACKGROUND

Gram-negative and Gram-positive bacteria produce beta-lactamase as factors to overcome beta-lactam antibiotics, causing their hydrolysis and impaired antimicrobial action. Class A beta-lactamase contains the chromosomal sulfhydryl reagent variable (SHV, point mutation variants of SHV-1), LEN (Klebsiella pneumoniae strain LEN-1), and other K. pneumoniae beta-lactamase (OKP) found mostly in Klebsiella’s phylogroups. The SHV known as extended-spectrum β-lactamase can inactivate most beta-lactam antibiotics. Class A also includes the worrisome plasmid-encoded Klebsiella pneumoniae carbapenemase (KPC-2), a carbapenemase that can inactivate most beta-lactam antibiotics, carbapenems, and some beta-lactamase inhibitors.

OBJECTIVES

So far, there is no 3D crystal structure for OKP-B, so our goal was to perform structural characterisation and molecular docking studies of this new enzyme.

METHODS

We applied a homology modelling method to build the OKP-B-6 structure, which was compared with SHV-1 and KPC-2 according to their electrostatic potentials at the active site. Using the DockThor-VS, we performed molecular docking of the SHV-1 inhibitors commercially available as sulbactam, tazobactam, and avibactam against the constructed model of OKP-B-6.

FINDINGS

From the point of view of enzyme inhibition, our results indicate that OKP-B-6 should be an extended-spectrum beta-lactamase (ESBL) susceptible to the same drugs as SHV-1.

MAIN CONCLUSIONS

This conclusion advantageously impacts the clinical control of the bacterial pathogens encoding OKP-B in their genome by using any effective, broad-spectrum, and multitarget inhibitor against SHV-containing bacteria.

Effects of feeding on different parts of Ailanthus altissima on the intestinal microbiota of Eucryptorrhynchus scrobiculatus and Eucryptorrhynchus brandti (Coleoptera: Curculionidae)

Eucryptorrhynchus brandti and Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae) are two monophagous weevil pests that feed on Ailanthus altissima (Mill.) Swingle but differ in their diet niche. In the field, adults of E. brandti prefer to feed on the trunk of A. altissima, whereas adults of E. scrobiculatus prefer to feed on the tender parts. We conducted Illumina sequencing of 16S rRNA to examine changes in bacterial diversity in the adults of these two weevil species after they fed on different parts of A. altissima (trunk, 2–3-year-old branches, annual branches, and petioles). Proteobacteria, Tenericutes, and Firmicutes were the dominant phyla in E. brandti (relative abundance was 50.64, 41.56, and 5.63%, respectively) and E. scrobiculatus (relative abundance was 78.63, 11.91, and 7.41%, respectively). At the genus level, Spiroplasma, endosymbionts2, Unclassified Enterobacteriaceae, and Lactococcus were dominant in E. brandti, and Unclassified Enterobacteriaceae, Wolbachia and Spiroplasma, and endosymbionts2 were dominant in E. scrobiculatus. Linear discriminant analysis effect size analysis revealed microbial biomarkers in the different treatment group of adults of both weevil species. Adults of E. brandti may require the trunk, and adults of E. scrobiculatus may require the petioles and annual branches to maintain the high diversity of their gut microbes. The results of this study indicate that feeding on different parts of A. altissima affects the composition and function of the microbes of E. brandti and the microbial composition of E. scrobiculatus. Variation in the abundance of Wolbachia and Spiroplasma in E. brandti and E. scrobiculatus is associated with dietary niche changes, and this might explain the evolution of reproductive isolation between these two sibling weevil species.

Molecular characterization of endophytic and ectophytic plant growth promoting bacteria isolated from tomato plants (Solanum lycopersicum L.) grown in different soil types

Background

Successful rhizosphere colonization by plant growth promoting rhizobacteria (PGPR) is of crucial importance to perform the desired plant growth promoting activities. Since rhizocompetence is a dynamic process influenced by surrounding environmental conditions. In the present study, we hypothesized that bacterial isolates obtained from different tomato plant microhabitats (balk soil, rhizosphere, endorhiza, phyllosphere, and endoshoot) grown in different soils (sand, clay, and peat moss) will show different rhizocompetence abilities.

Results

To evaluate this hypothesis, bacterial isolates were obtained from different plant microhabitats and screened for their phosphate solubilizing and nitrogen fixing activates. BOX-PCR fingerprint profiles showed high genotypic diversity among the tested isolates and that same genotypes were shared between different soils and/or plant microhabitats. 16S rRNA gene sequences of 25 PGP isolates, representing different plant spheres and soil types, were affiliated to eight genera: Enterobacter, Paraburkholderia, Klebsiella, Bacillus, Paenibacillus, Stenotrophomonas, Pseudomonas, and Kosakonia. The rhizocompetence of each isolate was evaluated in the rhizosphere of tomato plants grown on a mixture of the three soils. Different genotypes of the same bacterial species displayed different rhizocompetence potentials. However, isolates obtained from the above-ground parts of the plant showed high rhizocompetence. In addition, biological control-related genes, ituD and srfC, were detected in the obtained spore forming bacterial isolates.

Conclusion

This study evaluates, for the first time, the relationship between plant microhabitat and the rhizocompetence ability in tomato rhizosphere. The results indicated that soil type and plant sphere can influence both the genotypic diversity and rhizocompetence ability of the same bacterial species. Bacterial isolates obtained in this study are promising to be used as an environmentally friendly substitution of chemical fertilizers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00361-0.

Enabling Biological Nitrogen Fixation for Cereal Crops in Fertilized Fields

Agricultural productivity relies on synthetic nitrogen fertilizers, yet half of that reactive nitrogen is lost to the environment. There is an urgent need for alternative nitrogen solutions to reduce the water pollution, ozone depletion, atmospheric particulate formation, and global greenhouse gas emissions associated with synthetic nitrogen fertilizer use. One such solution is biological nitrogen fixation (BNF), a component of the complex natural nitrogen cycle. BNF application to commercial agriculture is currently limited by fertilizer use and plant type. This paper describes the identification, development, and deployment of the first microbial product optimized using synthetic biology tools to enable BNF for corn (Zea mays) in fertilized fields, demonstrating the successful, safe commercialization of root-associated diazotrophs and realizing the potential of BNF to replace and reduce synthetic nitrogen fertilizer use in production agriculture. Derived from a wild nitrogen-fixing microbe isolated from agricultural soils, Klebsiella variicola 137-1036 ("Kv137-1036") retains the capacity of the parent strain to colonize corn roots while increasing nitrogen fixation activity 122-fold in nitrogen-rich environments. This technical milestone was then commercialized in less than half of the time of a traditional biological product, with robust biosafety evaluations and product formulations contributing to consumer confidence and ease of use. Tested in multi-year, multi-site field trial experiments throughout the U.S. Corn Belt, fields grown with Kv137-1036 exhibited both higher yields (0.35 ± 0.092 t/ha ± SE or 5.2 ± 1.4 bushels/acre ± SE) and reduced within-field yield variance by 25% in 2018 and 8% in 2019 compared to fields fertilized with synthetic nitrogen fertilizers alone. These results demonstrate the capacity of a broad-acre BNF product to fix nitrogen for corn in field conditions with reliable agronomic benefits.

Plant-microbe-microbe interactions influence the faba bean nodule colonization by diverse endophytic bacteria

Legume root nodules harbor rhizobia and other non-nodulating endophytes known as nodule-associated bacteria (NAB) whose role in the legume symbiosis is still unknown. We analysed the genetic diversity of 34 NAB isolates obtained from the root nodules of faba bean grown under various soil conditions in Egypt using 16S rRNA and concatenated sequences of three housekeeping genes. All isolates were identified as members of the family Enterobacteriaceae belonging to the genera Klebsiella, Enterobacter and Raoultella. We identified nine enterobacterial genospecies, most of which have not been previously reported as NAB. All isolated strains harbored nifH gene sequences and most of them possessed plant growth-promoting (PGP) traits. Upon co-inoculation with an N2 fixing rhizobium (Rlv NGB-FR128), two strains (Enterobacter sichanensis NGB-FR97 and Klebsiella variicola NGB-FR116) significantly increased nodulation, growth and N-uptake of faba bean plants over the single treatments or the uninoculated control. The presence of these enterobacteria in nodules was significantly affected by the host plant genotype, symbiotic rhizobium genotype and endophyte genotype, indicating that the nodule colonization process is regulated by plant-microbe-microbe interactions. This study emphasizes the importance of nodule-associated enterobacteria and suggests their potential role in improving the effectiveness of rhizobial inoculants.

We and herbivores eat endophytes

Health depends on the diet and a vegetal diet promotes health by providing fibres, vitamins and diverse metabolites. Remarkably, plants may also provide microbes. Fungi and bacteria that reside inside plant tissues (endophytes) seem better protected to survive digestion; thus, we investigated the reported evidence on the endophytic origin of some members of the gut microbiota in animals such as panda, koala, rabbits and tortoises and several herbivore insects. Data examined here showed that some members of the herbivore gut microbiota are common plant microbes, which derived to become stable microbiota in some cases. Endophytes may contribute to plant fibre or antimetabolite degradation and synthesis of metabolites with the plethora of enzymatic activities that they display; some may have practical applications, for example, Lactobacillus plantarum found in the intestinal tract, plants and in fermented food is used as a probiotic that may defend animals against bacterial and viral infections as other endophytic-enteric bacteria do. Clostridium that is an endophyte and a gut bacterium has remarkable capabilities to degrade cellulose by having cellulosomes that may be considered the most efficient nanomachines. Cellulose degradation is a challenge in animal digestion and for biofuel production. Other endophytic-enteric bacteria may have cellulases, pectinases, xylanases, tannases, proteases, nitrogenases and other enzymatic capabilities that may be attractive for biotechnological developments, indeed many endophytes are used to promote plant growth. Here, a cycle of endophytic-enteric-soil-endophytic microbes is proposed which has relevance for health and comprises the fate of animal faeces as natural microbial inoculants for plants that constitute bacterial sources for animal guts.

Comprehensive genomic analysis and characterization of a new ST 174 type Klebsiella variicola strain isolated from chicken embryos

Klebsiella variicola is a widespread opportunistic pathogen that causes infections in humans and animals. Herein a novel Klebsiella strain, AHKv-S01, was isolated and identified from dead chicken embryos in Anhui, China. Its genome contained a circular chromosome of 5,505,304 bp, with 5244 protein-coding genes, and an integrative conjugative element region containing 79 ORF sequences. AHKv-S01 was given a new sequence type number-174. Phylogenetic analyses showed that rpoB partial nucleotide sequences were highly reliable for identifying Klebsiella spp. Most of the 340 unique genes of AHKv-S01 were involved in cell envelop biogenesis, transcription, transport, and metabolic processes. Moreover, AHKv-S01 was sensitive to several antibiotics, but it showed strong resistance to penicillins, macrolides, and lincosamide. The genome contained three drug efflux pump superfamilies, β-lactamase genes, and fosfomycin resistance-related genes. Most drug resistance genes showed amino acid mutations. Multiple virulence and pathogenic factors were also identified, and they were mainly related to adhesion, secretion, iron acquisition, and immune evasion. Chicken embryo lethality assay results revealed that the 7-day chicken embryo lethality rate was 80%, 40%, and 50% for AHKv-S01, K. pneumoniae ATCC10031, and K. pneumoniae CICC24714, respectively. The median lethal dose of AHKv-S01 was 39.9 CFU/embryo. Even low infection levels of AHKv-S01 caused a significant reduction in chicken embryo hatchability. Severe pathological changes to the liver, heart, and brain tissues of embryos infected with AHKv-S01 were observed, and these changes appeared earlier in the heart and brain than in the liver. To conclude, our results provide a foundation for further studies aiming to assess the potential risk of K. variicola to poultry populations and production yields.

A Klebsiella variicola Plasmid Confers Hypermucoviscosity-Like Phenotype and Alters Capsule Production and Virulence

Hypermucoviscosity (hmv) is a capsule-associated phenotype usually linked with hypervirulent Klebsiella pneumoniae strains. The key components of this phenotype are the RmpADC proteins contained in non-transmissible plasmids identified and studied in K. pneumoniae. Klebsiella variicola is closely related to K. pneumoniae and recently has been identified as an emergent human pathogen. K. variicola normally contains plasmids, some of them carrying antibiotic resistance and virulence genes. Previously, we described a K. variicola clinical isolate showing an hmv-like phenotype that harbors a 343-kb pKV8917 plasmid. Here, we investigated whether pKV8917 plasmid carried by K. variicola 8917 is linked with the hmv-like phenotype and its contribution to virulence. We found that curing the 343-kb pKV8917 plasmid caused the loss of hmv, a reduction in capsular polysaccharide (P < 0.001) and virulence. In addition, pKV8917 was successfully transferred to Escherichia coli and K. variicola strains via conjugation. Notably, when pKV8917 was transferred to K. variicola, the transconjugants displayed an hmv-like phenotype, and capsule production and virulence increased; these phenotypes were not observed in the E. coli transconjugants. These data suggest that the pKV8917 plasmid carries novel hmv and capsule determinants. Whole-plasmid sequencing and analysis revealed that pKV8917 does not contain rmpADC/rmpA2 genes; thus, an alternative mechanism was searched. The 343-kb plasmid contains an IncFIB backbone and shares a region of ∼150 kb with a 99% identity and 49% coverage with a virulence plasmid from hypervirulent K. variicola and multidrug-resistant K. pneumoniae. The pKV8917-unique region harbors a cellulose biosynthesis cluster (bcs), fructose- and sucrose-specific (fru/scr) phosphotransferase systems, and the transcriptional regulators araC and iclR, respectively, involved in membrane permeability. The hmv-like phenotype has been identified more frequently, and recent evidence supports the existence of rmpADC/rmpA2-independent hmv-like pathways in this bacterial genus.

Evaluation of two rapid molecular test systems to establish an algorithm for fast identification of bacterial pathogens from positive blood cultures

Fast identification of pathogens directly from positive blood cultures is of highest importance to supply an adequate therapy of bloodstream infections (BSI). There are several platforms providing molecular-based identification, detection of antimicrobial resistance genes, or even a full antimicrobial susceptibility testing (AST). Two of such test systems allowing rapid diagnostics were assessed in this study: The Biofire FilmArray® and the Genmark ePlex®, both fully automated test system with a minimum of hands-on time. Overall 137 BSI episodes were included in our study and compared to conventional culture–based reference methods. The FilmArray® is using one catridge including a panel for the most common bacterial and fungal BSI pathogens as well as selected resistance markers. The ePlex® offers three different cartridges for detection of Gram-positives, Gram-negatives, and fungi resulting in a broader panel including also rare pathogens, putative contaminants, and more genetic resistance markers. The FilmArray® and ePlex® were evaluated for all 137 BSI episodes with FilmArray® detecting 119 and ePlex® detecting 128 of these. For targets on the respective panel of the system, the FilmArray® generated a sensitivity of 98.9% with 100% specificity on Gram-positive isolates. The ePlex® system generated a sensitivity of 94.7% and a specificity of 90.7% on Gram-positive isolates. In each case, the two systems performed with 100% sensitivity and specificity for the detection of Gram-negative specimens covered by each panel. In summary, both evaluated test systems showed a satisfying overall performance for fast pathogen identification and are beneficial tools for accelerating blood culture diagnostics of sepsis patients.

Identification of Klebsiella Variicola T29A Genes Involved In Tolerance To Desiccation

Introduction:

Several plant-beneficial bacteria have the capability to promote the growth of plants through different mechanisms. The survival of such bacteria could be affected by environmental abiotic factors compromising their capabilities of phytostimulation. One of the limiting abiotic factors is low water availability.

Materials and Methods:

In extreme cases, bacterial cells can suffer desiccation, which triggers harmful effects on cells. Bacteria tolerant to desiccation have developed different strategies to cope with these conditions; however, the genes involved in these processes have not been sufficiently explored.Klebsiella variicolaT29A is a beneficial bacterial strain that promotes the growth of corn plants and is highly tolerant to desiccation. In the present work, we investigated genes involved in desiccation tolerance.

Results & Discussion:

As a result, a library of 8974 mutants of this bacterial strain was generated by random mutagenesis with mini-Tn5 transposon, and mutants that lost the capability to tolerate desiccation were selected. We found 14 sensitive mutants; those with the lowest bacterial survival rate contained mini-Tn5 transposon inserted into genes encoding a protein domain related to BetR, putative secretion ATPase and dihydroorotase. The mutant in the betR gene had the lowest survival; therefore, the mutagenized gene was validated using specific amplification and sequencing.

Conclusion:

Trans complementation with the wild-type gene improved the survival of the mutant under desiccation conditions, showing that this gene is a determinant for the survival ofK. variicolaT29A under desiccation conditions.

Molecular epidemiology of Klebsiella variicola obtained from different sources

Klebsiella variicola is considered an emerging pathogen in humans and has been described in different environments. K. variicola belongs to Klebsiella pneumoniae complex, which has expanded the taxonomic classification and hindered epidemiological and evolutionary studies. The present work describes the molecular epidemiology of K. variicola based on MultiLocus Sequence Typing (MLST) developed for this purpose. In total, 226 genomes obtained from public data bases and 28 isolates were evaluated, which were mainly obtained from humans, followed by plants, various animals, the environment and insects. A total 166 distinct sequence types (STs) were identified, with 39 STs comprising at least two isolates. The molecular epidemiology of K. variicola showed a global distribution for some STs was observed, and in some cases, isolates obtained from different sources belong to the same ST. Several examples of isolates corresponding to kingdom-crossing bacteria from plants to humans were identified, establishing this as a possible route of transmission. goeBURST analysis identified Clonal Complex 1 (CC1) as the clone with the greatest distribution. Whole-genome sequencing of K. variicola isolates revealed extended-spectrum β-lactamase- and carbapenemase-producing strains with an increase in pathogenicity. MLST of K. variicola is a strong molecular epidemiological tool that allows following the evolution of this bacterial species obtained from different environments.

Klebsiella variicola: an emerging pathogen in humans

The Klebsiella pneumoniae complex comprises seven K. pneumoniae-related species, including K. variicola. K. variicola is a versatile bacterium capable of colonizing different hosts such as plants, humans, insects and animals. Currently, K. variicola is gaining recognition as a cause of several human infections; nevertheless, its virulence profile is not fully characterized. The clinical significance of K. variicola infection is hidden by imprecise detection methods that underestimate its real prevalence; however, several methods have been developed to correctly identify this species. Recent studies of carbapenemase-producing and colistin-resistant strains demonstrate a potential reservoir of multidrug-resistant genes. This finding presents an imminent scenario for spreading antimicrobial resistant genes among close relatives and, more concerningly, in clinical and environmental settings. Since K. variicola was identified as a novel bacterial species, different research groups have contributed findings elucidating this pathogen; however, important details about its epidemiology, pathogenesis and ecology are still missing. This review highlights the most significant aspects of K. variicola, discussing its different phenotypes, mechanisms of resistance, and virulence traits, as well as the types of infections associated with this pathogen.

Population Structure, Antibiotic Resistance, and Uropathogenicity of Klebsiella variicola

Infections caused by antibiotic-resistant bacterial pathogens are a growing public health threat. Understanding of pathogen relatedness and biology is imperative for tracking outbreaks and developing therapeutics. Here, we detail the phylogenetic structure of 145 K. variicola genomes from different continents. Our results have important clinical ramifications as high-risk antibiotic resistance genes are present in K. variicola genomes from a variety of geographic locations and as we demonstrate that K. variicola clinical isolates can establish higher bladder titers than K. pneumoniae. Differential presence of these pilus genes inK. variicola isolates may indicate adaption for specific environmental niches. Therefore, due to the potential of multidrug resistance and pathogenic efficacy, identification of K. variicola and K. pneumoniae to a species level should be performed to optimally improve patient outcomes during infection. This work provides a foundation for our improved understanding of K. variicola biology and pathogenesis.

Klebsiella variicola is a member of the Klebsiella genus and often misidentified as Klebsiella pneumoniae or Klebsiella quasipneumoniae. The importance of K. pneumoniae human infections has been known; however, a dearth of relative knowledge exists for K. variicola. Despite its growing clinical importance, comprehensive analyses of K. variicola population structure and mechanistic investigations of virulence factors and antibiotic resistance genes have not yet been performed. To address this, we utilized in silico, in vitro, and in vivo methods to study a cohort of K. variicola isolates and genomes. We found that the K. variicola population structure has two distant lineages composed of two and 143 genomes, respectively. Ten of 145 K. variicola genomes harbored carbapenem resistance genes, and 6/145 contained complete virulence operons. While the β-lactam bla_LEN and quinolone oqxAB antibiotic resistance genes were generally conserved within our institutional cohort, unexpectedly 11 isolates were nonresistant to the β-lactam ampicillin and only one isolate was nonsusceptible to the quinolone ciprofloxacin. K. variicola isolates have variation in ability to cause urinary tract infections in a newly developed murine model, but importantly a strain had statistically significant higher bladder CFU than the model uropathogenic K. pneumoniae strain TOP52. Type 1 pilus and genomic identification of altered fim operon structure were associated with differences in bladder CFU for the tested strains. Nine newly reported types of pilus genes were discovered in the K. variicola pan-genome, including the first identified P-pilus in Klebsiella spp.

Nitrogen Fixation in Cereals

Cereals such as maize, rice, wheat and sorghum are the most important crops for human nutrition. Like other plants, cereals associate with diverse bacteria (including nitrogen-fixing bacteria called diazotrophs) and fungi. As large amounts of chemical fertilizers are used in cereals, it has always been desirable to promote biological nitrogen fixation in such crops. The quest for nitrogen fixation in cereals started long ago with the isolation of nitrogen-fixing bacteria from different plants. The sources of diazotrophs in cereals may be seeds, soils, and even irrigation water and diazotrophs have been found on roots or as endophytes. Recently, culture-independent molecular approaches have revealed that some rhizobia are found in cereal plants and that bacterial nitrogenase genes are expressed in plants. Since the levels of nitrogen-fixation attained with nitrogen-fixing bacteria in cereals are not high enough to support the plant’s needs and never as good as those obtained with chemical fertilizers or with rhizobium in symbiosis with legumes, it has been the aim of different studies to increase nitrogen-fixation in cereals. In many cases, these efforts have not been successful. However, new diazotroph mutants with enhanced capabilities to excrete ammonium are being successfully used to promote plant growth as commensal bacteria. In addition, there are ambitious projects supported by different funding agencies that are trying to genetically modify maize and other cereals to enhance diazotroph colonization or to fix nitrogen or to form nodules with nitrogen-fixing symbiotic rhizobia.

Draft Genome Sequences of Endophytic Isolates of Klebsiella variicola and Klebsiella pneumoniae Obtained from the Same Sugarcane Plant

Endophytic Klebsiella variicola KvMx2 and Klebsiella pneumoniae KpMx1 isolates obtained from the same sugarcane stem were used for whole-genome sequencing. The genomes revealed clear differences in essential genes for plant growth, development, and detoxification, as well as nitrogen fixation, catalases, cellulases, and shared virulence factors described in the K. pneumoniae pathogen.