Isolation and characterization of a newly chrysene-degrading Achromobacter aegrifaciens.

Polycyclic aromatic hydrocarbons (PAHs) are considered substances of potential human health hazards because of their resistance to biodegradation and carcinogenic index. Chrysene is a PAH with a high molecular weight (HMW) that poses challenges for its elimination from the environment. However, bacterial degradation is an effective, environmentally friendly, and cost-effective solution. In our study, we isolated a potential chrysene-degrading bacteria from crude oil-contaminated seawater (Bizerte, Tunisia). Based on 16SrRNA analysis, the isolate S5 was identified as Achromobacter aegrifaciens. Furthermore, the results revealed that A. aegrifaciens S5 produced a biofilm on polystyrene at 20 °C and 30 °C, as well as at the air-liquid (A-L) interface. Moreover, this isolate was able to swim and produce biosurfactants with an emulsification activity (E24%) over 53%. Chrysene biodegradation by isolate S5 was clearly assessed by an increase in the total viable count. Confirmation was obtained via gas chromatography-mass spectrometry (GC-MS) analyses. A. aegrifaciens S5 could use chrysene as its sole carbon and energy source, exhibiting an 86% degradation of chrysene on day 7. In addition, the bacterial counts reached their highest level, over 25 × 1020 CFU/mL, under the conditions of pH 7.0, a temperature of 30 °C, and a rotary speed of 120 rpm. Based on our findings, A. aegrifaciens S5 can be a potential candidate for bioremediation in HMW-PAH-contaminated environments.

Comparative genomics reveals the acquisition of mobile genetic elements by the plant growth-promoting Pantoea eucrina OB49 in polluted environments.

Heavy metal-tolerant plant growth-promoting bacteria (PGPB) have gained popularity in bioremediation in recent years. A genome-assisted study of a heavy metal-tolerant PGPB Pantoea eucrina OB49 isolated from the rhizosphere of wheat grown on a heavy metal-contaminated site is presented. Comparative pan-genome analysis indicated that OB49 acquired heavy metal resistance genes through horizontal gene transfer. On contigs S10 and S12, OB49 has two arsRBCH operons that give arsenic resistance. On the S12 contig, an arsRBCH operon was discovered in conjunction with the merRTPCADE operon, which provides mercury resistance. P. eucrina OB49 may be involved in an ecological alternative for heavy metal remediation and growth promotion of wheat grown in metal-polluted soils. Our results suggested the detection of mobile genetic elements that harbour the ars operon and the fluoride resistance genes adjacent to the mer operon.

First Report of IMI-2-Producing Enterobacter bugandensis and CTX-M-55-Producing Escherichia coli isolated from Healthy Volunteers in Tunisia.

The aim of this study was to characterize the prevalence of fecal carriage of extended-spectrum beta-lactamases and carbapenemase-producing Gram-negative bacteria among healthy humans in Tunisia. Fifty-one rectal swabs of healthy volunteers were plated on MacConkey agar plates supplemented with cefotaxime or imipenem. The occurrences of resistance genes, integrons, and phylogroup typing were investigated using PCR and sequencing. The genetic relatedness of isolates was determined by pulsed-field-gel-electrophoresis (PFGE) and multilocus-sequence-typing (MLST). Whole-genome-sequencing (WGS) was performed for the carbapenem-resistant isolate. Sixteen ESBL-producing Escherichia coli isolates and one carbapenem-resistant Enterobacter bugandensis were detected out of the fifty-one fecal samples. The ESBL-producing E. coli strains contained genes encoding CTX-M-15 (n = 9), CTX-M-1 (n = 3), CTX-M-27 (n = 3), and CTX-M-55 (n = 1). Three CTX-M-1-producers were of lineages ST131, ST7366, and ST1158; two CTX-M-15-producers belonged to lineage ST925 and ST5100; one CTX-M-27-producer belonged to ST2887, and one CTX-M-15-producer belonged to ST744. Six isolates contained class 1 integrons with the following four gene cassette arrangements: dfrA5 (two isolates), dfrA12-orf-aadA2 (two isolates), dfrA17-aadA5 (one isolate), and aadA1 (one isolate). E. bugandensis belonged to ST1095, produced IMI-2 carbapenemase, and contained qnrE1 and fosA genes. A genome-sequence analysis of the E. bugandensis strain revealed new mutations in the blaACT and qnr genes. Our results reveal an alarming rate of ESBL-E. coli in healthy humans in Tunisia and the first description of IMI-2 in E. bugandensis.

First insights into the microbiome of Tunisian Hyalomma ticks gained through next-generation sequencing with a special focus on H. scupense.

Ticks are one of the most important vectors of several pathogens affecting humans and animals. In addition to pathogens, ticks carry diverse microbiota of symbiotic and commensal microorganisms. In this study, we have investigated the first Tunisian insight into the microbial composition of the most dominant Hyalomma species infesting Tunisian cattle and explored the relative contribution of tick sex, life stage, and species to the diversity, richness and bacterial species of tick microbiome. In this regard, next generation sequencing for the 16S rRNA (V3-V4 region) of tick bacterial microbiota and metagenomic analysis were established. The analysis of the bacterial diversity reveals that H. marginatum and H. excavatum have greater diversity than H. scupense. Furthermore, microbial diversity and composition vary according to the tick's life stage and sex in the specific case of H. scupense. The endosymbionts Francisella, Midichloria mitochondrii, and Rickettsia were shown to be the most prevalent in Hyalomma spp. Rickettsia, Francisella, Ehrlichia, and Erwinia are the most common zoonotic bacteria found in Hyalomma ticks. Accordingly, Hyalomma ticks could represent potential vectors for these zoonotic bacterial agents.

Fungal Community Investigation from Propolis Natural Products: Diversity and Antibacterial Activities Evaluation.

Discovering new species and interesting bioactive metabolites from customary sources is becoming progressively laborious. Propolis constitutes the largest diversified reserve of microbial constituents in the beehive. However, fungal communities associated with these environments remain insufficiently established. We present the first detailed investigation of the cultivable fungal community associated with Tunisian propolis, and we evaluate its antibacterial properties against pathogenic bacteria. A total of 80 fungal strains were isolated from propolis samples derived from seven different Tunisian locations. The majority of the isolated fungi were classified as Ascomycota (97.5%), and only 2.5% belonged to Basidiomycota. Our collection was clustered into 15 genera, among which Coniochaeta (36.25%), Aspergillus (15%), Penicillium (13.75%), Cladosporium (10%), Fusarium (7.5%), Didymella (5%), and Alternaria (3.75%) were the most common. Evaluation of the antibacterial activity revealed that 25.6% of the total community showed a broad range of antibacterial activity. Particularly, the Penicillium griseofulvum CC8 strain has manifested the strongest inhibitory effects against all the tested bacteria.

Molecular signature of phylogenetic relationships and demographic history of Tunisian Mactra stultorum: Evidence from mitochondrial and nuclear DNA data.

The genetic structure of Mactra stultorum is inferred from partial sequence of a mitochondrial cox1gene and of the internal transcribed spacer region ITS1. The samples with two colors of shell (white and brown) were collected from three sites belonging to the Tunisian coasts: Kalaât El Andalous (KA) and Soliman (SM) and Gabes (GM)). The phylogenetic trees obtained from the 2 markers are similar and subdivided samples into 3 distinct clades; clade (1) regrouped GM, clade (2) regrouped KS (KS contains samples from SM and KAa) and clade (3) is formed by KAb. Using the external sequences from genbank, it can be suggested that M. stultorum from the three clades KS, GM and KAb are three subspecies. The two sympatric M. stultorum from KA (KAa and KAb) appear to be genetically isolated showing a high genetic distance and no common haplotypes where the shell color serves for segregating marker. A total of 29 and 18 haplotypes were detected in the examined cox1 and ITS1 regions, respectively. Our study revealed higher levels of genetic diversity for ITS1 compared to cox1. For both markers, significant clinal changes in haplotypes frequencies between the north and the south populations supported by the absence of common haplotypes were observed. The demographic history of M. stultorum populations has been assessed using neutral tests and mismatch distribution for cox1 marker. A unimodal curve of the Mismatch's distribution and negative significant neutral tests suggested a recent sudden demographic expansion for GM.

Pseudomonas knackmussii MLR6, a rhizospheric strain isolated from halophyte, enhances salt tolerance in Arabidopsis thaliana.

AIMS: The study aimed for evaluate the efficacy of Pseudomonas knackmussii MLR6 on growth promotion, photosynthetic responses, pigment contents and gene expression of the plant model Arabidopsis thaliana under NaCl stress. METHODS AND RESULTS: The strain MLR6 was isolated from the rhizopshere of the halophyte Salsola tetrandra collected from a natural saline Algerian soil. Results showed the ability of MLR6 to induce plant growth promoting traits even under NaCl stress. The inoculation with MLR6 improved the stomatal conductance, the transpiration rate, the total chlorophyll and carotenoids contents under salt stress. It conferred also an increase of fresh/dry weight as well as plant height. MLR6 inoculation further provided a positive effect on cell membrane stability by reducing the electrolyte leakage and priming the ROS accumulation after the salt exposition. Additionally, the expression of NHX1, HKT1, SOS2, and SOS3 as well as SAG13 and PR1 was maintained in MLR6-bacterized plant at a similar level of controls. CONCLUSIONS: The inoculation of Arabidopsis thaliana with MLR6 improves plant growth and reduces damages caused by salt stress. SIGNIFICANCE AND IMPACT OF STUDY: The use of Pseudomonas knackmussii MLR6 appears as a promising strategy to improve the sustainable agriculture under saline conditions. This article is protected by copyright. All rights reserved.