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In the present investigation, five novel Cr(VI) reducing bacteria were isolated from tannery effluents and solid wastes and identified as Kosakonia cowanii MKPF2, Klebsiella pneumonia MKPF5, Acinetobacter gerneri MKPF7, Klebsiella variicola MKPF8 and Serratia marcescens MKPF12 by 16S rDNA gene sequence analysis. The maximum tolerance concentration of Cr(VI) as K2Cr2O7 of the bacterial isolates was varying up to 2000 mg/L. Among the investigated bacterial isolates, A. gerneri MKPF7 was best in terms of reduction rate. The optimum temperatures for growth and Cr(VI) reduction by the bacterial isolates were 35 and 40 °C, respectively except A. gerneri MKPF7 which grew and reduced Cr(VI) optimally at 40 °C. The optimum pH for growth and Cr(VI) reduction by K. cowanii MKPF2, A. gerneri MKPF7 and S. marcescens MKPF12 was 7.0 whereas the optimum pH for growth and Cr(VI) reduction by K. pneumoniae MKPF5 and K. variicola MKPF8 were 7.0, 8.0 and 6.0, 7.0, respectively. All the bacterial isolates showed maximum tolerance against Ni2+ and Zn2+ whereas minimum tolerance was observed against Hg2+ and Cd2+. The bacteria isolated in the present study thus can be used as eco-friendly biological expedients for the remediation and detoxification of Cr(VI) from the contaminated environments.

The purpose of this study is to enhance the biodegradability of atrazine with FH-1 and NJ-1 alone by selecting the mixing ratio, optimizing the culture medium and conditions. The results showed that FH-1 and NJ-1 have the best biodegradation effect on atrazine being mixed in a volume ratio of 3:2. In a single factor experiment, sucrose and NH4Cl provided carbon and nitrogen sources for the mixed bacteria. Subsequently, composition of fermentation medium was further optimized using Box-Behnken design of response surface methodology. Based on the results, growth of mixed bacteria and biodegradation of atrazine performed best effects with a biodegradation rate of 85.6% when sucrose and NH4Cl amounts were 35.30 g/L and 10.28 g/L. The optimal medium condition was 10% inoculum of mixed bacteria, with initial atrazine concentration of 50 mg/L, neutral or weakly alkaline pH value, 30°C. The biodegradation rate reached 97.4%, 11.8% higher than the unoptimized condition.

Background Klebsiella variicola and K. quasipneumoniae are new species distinguishable from K. pneumoniae but they are often misidentified as K. pneumoniae in clinical settings. Several reports have demonstrated the possibility that the virulence factors and clinical features differ among these three phylogroups. In this study, we aimed to clarify whether there were differences in clinical and bacterial features between the three phylogroups isolated from patients with bloodstream infections (BSIs) in Japan. Methods Isolates from all patients with BSIs caused by K. pneumoniae admitted to two hospitals between 2014 and 2017 ( n  = 119) were included in the study. Bacterial species were identified via sequence analysis, and their virulence factors and serotypes were analyzed via multiplex PCR results. Clinical data were retrieved from medical records. Results Of the 119 isolates, 21 (17.7%) were identified as K. variicola and 11 (9.2%) as K. quasipneumoniae ; K1 serotype was found in 16 (13.4%), and K2 serotype in 13 (10.9%). Significant differences in the prevalence of rmpA , iutA , ybtS , entB and kfu ( p  < 0.001), and allS genes ( p  < 0.05) were found between the three phylogroups. However, there were no significant differences in clinical features, including the 30-day mortality rate, between the three organisms, although K. variicola was more frequently detected in patients over 80 years old compared with other Klebsiella species ( p  < 0.005), and K. quasipneumoniae more frequently occurred in patients with malignancy ( p  < 0.05). Conclusions Our findings demonstrated the differences in bacterial pathogenicity and clinical features among these three phylogroups. Further epidemiological studies into BSI caused by Klebsiella species are warranted.

Nitrogen (N) is an essential plant nutrient, but low and variable plant‐available N levels in agricultural soils often limit maximum grain production. The objective of this study was to determine if a free‐living nitrogen‐fixing bacterial inoculant (NFI) could supply biologically‐fixed N as an additional N source and if this enhances maize (Zea mays L.) N uptake and grain yield. Maize was grown at four site‐years in Illinois during 2019–2021. The NFI, a mixture of edited Klebsiella variicola and Kosakonia sacchari, was applied in furrow at planting with urea‐N rates from 0 to 225 kg N ha−1. Using quadratic regression models, across N rates, the NFI supplemented the fertilizer‐N equivalent of 38.5 or 12.1 kg N ha−1 at V8 or R1, respectively. Increases in N accumulation were observed in all plant fractions, and δ15N abundance measurements confirmed that some of this additional N was derived from biological N fixation. The NFI treatment increased N accumulation by an average of 4.8% and 3.7% at V8 and R1, respectively, which was the result of greater biomass, with no effect on plant N concentration. Application of NFI resulted in an average of 1.5% more kernels m−2 and 0.11 Mg ha−1 more grain yield. This work reveals that NFI can provide an additional source of N for maize production but identifies that the season‐long benefit of fixed‐N from an NFI is yet to be fully optimized. Core Ideas N‐fixing inoculant supplements maize with atmospheric N2 during vegetative growth. Inoculant‐supplied N increases are a function of plant biomass, not tissue concentration. Biomass response to inoculation is greatest at V8 (+4.8%) but diminishes by maturity. Averaged over N rates, grain yield was increased by 1.2% when inoculated. Plain Language Summary Nitrogen is often the most limiting nutrient for increased maize yields, but extra fertilizer may be lost to waterways and the air. Nitrogen‐fixing bacterial inoculants can convert nitrogen from the air into a usable form in the soil near the plant roots. Yet, maize plants need nitrogen at certain times and amounts to be useful to grow and make yield. We wanted to know if a nitrogen‐fixing bacteria inoculation mix can replace some reliance on fertilizer, when maize takes up this nitrogen and where it goes in the plant, and if grain yield changes. Supplying the inoculant at planting in combination with low rates of fertilizer (45–135 kg nitrogen ha−1) increased maize vegetative growth, nitrogen accumulation, kernel number, and yield (on average 0.11 Mg ha−1 more yield) and was equal to 12–38 kg nitrogen ha−1 of fertilizer. This nitrogen‐fixing inoculant mix added to the nitrogen fertilizer, mostly early, for small, but significant, increases in maize plant growth and yield.

We report a clonal outbreak of multidrug-resistant (MDR) Klebsiella variicola (sequence type [ST] 771) in a Bangladeshi neonatal unit from October 2016 to January 2017, associated with high mortality (54.5%). During the outbreak, K. variicola ST771 acquired an MDR plasmid harboring blaNDM-1, linked to high exposure to ceftriaxone and amikacin.

Klebsiella variicola is considered a newly emerging human pathogen. Clinical isolates of carbapenemase and broad-spectrum β-lactamase-producing K. variicola remain relatively uncommon. A strain of K. variicola 4253 was isolated from a clinical sample, and was identified to carry the bla and bla genes. This study aims to discern its antibiotic resistance phenotype and genomic characteristics. Species identification was conducted using MALDI-TOF/MS. PCR identification confirmed the presence of the bla and bla genes. Antibiotic resistance phenotype and genomic characteristics were detected by antimicrobial susceptibility testing and whole-genome sequencing. Plasmid characterization was carried out through S1-PFGE, conjugation experiments, Southern blot, and comparative genomic analysis. K. variicola 4253 belonged to ST347, and demonstrated resistance to broad-spectrum β-lactamase drugs and tigecycline while being insensitive to imipenem and meropenem. The bla and bla genes harbored on the plasmid p4253-imp. The replicon type of p4253-imp was identified as IncHI5B, representing a multidrug-resistant plasmid capable of horizontal transfer and mediating the dissemination of drug resistance. The bla gene was located on the In809-like integrative element (Intl1-bla -aacA4-catB3), which circulates in Acinetobacter and Enterobacteriaceae. This study reports the presence of a strain of K. variicola, which is insensitive to tigecycline, carrying a plasmid harboring bla and bla . It is highly likely that the strain acquired this plasmid through horizontal transfer. The bla array (Intl1-bla -aacA4-catB3) is also mobile in Acinetobacter and Enterobacteriaceae. So it is essential to enhance clinical awareness and conduct epidemiological surveillance on multidrug-resistant K. variicola, conjugative plasmids carrying bla , and the In809 integrative element.

The present study investigated biodegradation and removal of Reactive Red 198 (RR198) dye from aqueous environments using a new bacterial consortium isolated from textile wastewater sludge on laboratory scale via batch study. Two bacterial species, Enterococcus faecalis (EF) and Klebsiella variicola (KV), were identified after isolation, through biochemical assays, Polymerase chain reaction (PCR), and 16S rRNA gene sequencing. To determine their ability to biodegrade RR198 dye, physicochemical parameters, including bacterial concentration, time, pH, and temperature, were tested; the results showed that the best conditions included a bacterial concentration of 3.5 mL × 105 cells/mL and incubation time of 72 h. Under such conditions, the removal efficiency of RR198 dye at an initial concentration of 10–25 mg/L was more than 98%; however, for concentrations of 50, 75, and 100 mg/L, removal efficiency was reduced to 55.62%, 25.82%, and 15.42%, respectively (p = 0.005). The highest removal efficiency occurred at pH 8.0, reaching 99.26% after 72 h of incubation. With increasing the incubation temperature from 25 °C to 37 °C, removal efficiency increased from 71.71 to 99.26% after 72 h of incubation, and increasing the temperature from 37 to 45 °C, the removal efficiency was reduced (p ≤ 0.001). Therefore, the EF–KV bacterial consortium can be used for efficient removal of RR198 dye from textile effluent.

Phosphorus (P) is an essential macronutrient for plant growth that plays a critical role in photosynthesis, DNA synthesis, and energy transfer. Phosphorus deficiency is a major limitation to plant growth and agricultural productivity globally. This deficiency arises from a combination of soil composition, agricultural practices, plant physiological responses, and environmental factors. Understanding these factors is crucial for developing strategies to mitigate phosphorus deficiency and improve crop yields. The isolation, characterization, and application of potent indigenous bacteria capable of phosphorus solubilization are of significant importance in acidic soils to overcome the challenges posed by phosphorus fixation. In this study, we report the genome sequencing of Klebsiella variicola strain PSEG-1, isolated from the gut of the earthworm Aporrectodea sp. that exhibits notable phosphorus solubilization ability. Genomic analysis reveals that the PSEG-1 genome comprises a single chromosome of 5.69 Mb, with a GC content of 57.07%, and encodes 5,596 protein-coding sequences, 4 rRNA genes, and 80 tRNA genes. Functional annotation of the genome identified 19 distinct categories of protein-coding genes, with a notable representation of genes involved in amino acid transport and metabolism, carbohydrate transport and metabolism, and transcriptional regulation. Notably, the genetic repertoire of PSEG-1 comprises 37 genes implicated in organic acid metabolism, 5 genes associated with phosphatase activity, and 2 genes directly involved in phosphate metabolism. These findings highlight the potential of K. variicola PSEG-1 to enhance phosphorus availability in nutrient-deficient environments.

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 in K. 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. IMPORTANCE 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 in K. 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.

Background Klebsiella variicola is an emerging multidrug‑resistant opportunistic pathogen that is often misidentified as K. pneumoniae in clinical laboratories. Here, we investigated four NDM‑9-producing K. variicola ST363‑KL151 isolates from patients treated at a tertiary-care centre in China. Methods Whole-genome sequencing and genomic analyses were performed to confirm species identity, define molecular characteristics, and identify resistance determinants. Core-genome SNP analysis was used to assess phylogenetic relatedness to international strains. Carbapenem-resistance transferability was evaluated by conjugation to E. coli . Biofilm formation, epithelial-cell invasion/cytotoxicity, serum bactericidal resistance, and virulence in a Galleria mellonella infection model were assessed. Results Antimicrobial susceptibility testing revealed a broad resistance profile encompassing β‑lactams (including carbapenems), aminoglycosides, fluoroquinolones, and fosfomycin, while retaining susceptibility to tigecycline. One isolate demonstrated elevated polymyxin resistance with an MIC of 64 mg/L, mediated by mgrB truncation (p.Gln30*). Whole‑genome sequencing identified a IncHI2A plasmid carrying a unique IS 26 ‑flanked bla NDM‑9 composite transposon adjacent to a mercury resistance operon, and conjugation assays confirmed transferable carbapenem resistance. Phylogenetic analysis placed the ST363-KL151 isolates in a monophyletic clade with a Norwegian strain collected in 2015. Although hypervirulence plasmids and classical virulence loci were absent, the isolates showed substantial biofilm formation and serum resistance, but only moderate cytotoxicity in epithelial cells and limited lethality in Galleria mellonella compared with the hypervirulent control NTUH-K2044. Conclusions These findings identify NDM‑9‑producing K. variicola ST363‑KL151 as a multidrug‑resistant lineage, emphasizing the need for accurate species identification and genome‑based surveillance to prevent its further clinical spread.