Analysis of endophytic actinobacteria species diversity in the stem of <Emphasis Type="Italic">Gynura cusimbua</Emphasis> by 16S rRNA gene clone library

Endophytic actinobacteria that lived in any associations with plant tissues represented a rather unexplored area of actinobacteria compared with soils. Gynura cusimbua was a kind of medicinal plant which had prevention effects for high blood pressure, coronary heart disease, Alzheimer’s disease, atherosclerosis, etc. Endophytic actinobacteria of G. cusimbua might produce some secondary metabolites which had the same function as their host. Stem samples of G. cusimbua collected from Hainan Province were used to study their endophytic actinobacteria to find some new compounds. In order to avoid vast proportions of the host plant DNA in the metagenomic library, the strategies of enrichment of the microorganism cells after tissue digestion and exclusion of 16S rRNA gene derived from the plastid by digested with PvuII were used. Two sets of actinobacteria specific primers were used for targeting endophytic actinobacteria from metagenomic library. 63 positive clones of actinobacteria were selected for sequencing and constructing the phylogenetic tree of 16S rRNA gene, and the 16S rRNA gene sequence of 59 strains among them had higher similar to the closest type strain and belonged to Microbacterium, Arthrobacter, Micrococcus, Curtobacterium, Okibacterium, Quadrisphaera and Kineococcus, respectively. Others were in low similarity and belonged to unclassified Micrococcineae, unclassified Intrasporangiaceae and unclassified Microbacteriaceae.     

Diversity of endophytic fungal and bacterial communities in <Emphasis Type="Italic">Ilex paraguariensis</Emphasis> grown under field conditions

The composition and diversity of the endophytic community associated with yerba mate (Ilex paraguariensis) was investigated using culture-depending methods. Fungi were identified based on their micromorphological characteristics and internal transcribed spacer rDNA sequence analysis; for bacteria 16S rDNA sequence analysis was used. Fungal and bacterial diversity did not show significant differences between organ age. The highest fungal diversity was registered during fall season and the lowest in winter. Bacterial diversity was higher in stems and increased from summer to winter, in contrast with leaves, which decreased. The most frequently isolated fungus was Fusarium, followed by Colletotrichum; they were both present in all the sampling seasons and organ types assayed. Actinobacteria represented 57.5 % of all bacterial isolates. The most dominant bacterial taxa were Curtobacterium and Microbacterium. Other bacteria frequently found were Methylobacterium, Sphingomonas, Herbiconiux and Bacillus. Nitrogen fixation and phosphate solubilization activity, ACC deaminase production and antagonism against plant fungal pathogens were assayed in endophytic bacterial strains. In the case of fungi, strains of Trichoderma, Penicillium and Aspergillus were assayed for antagonism against pathogenic Fusarium sp. All microbial isolates assayed showed at least one growth promoting activity. Strains of Bacillus, Pantoea, Curtobacterium, Methylobacterium, Brevundimonas and Paenibacillus had at least two growth-promoting activities, and Bacillus, Paenibacillus and the three endophytic fungi showed high antagonistic activity against Fusarium sp. In this work we have made a wide study of the culturable endophytic community within yerba mate plants and found that several microbial isolates could be considered as potential inoculants useful for improving yerba mate production.     

Production of vineomycin A1 and chaetoglobosin A by <Emphasis Type="Italic">Streptomyces</Emphasis> sp. PAL114

An actinobacteria strain PAL114, isolated from a Saharan soil in Algeria, produces bioactive compounds. Morphological and chemical studies indicated that this strain belongs to the genus Streptomyces. Analysis of the 16S rRNA gene sequence showed a similarity level of 99.8 % with S. griseoflavus LMG 19344^T, the most closely related species. Two bioactive compounds, named P44 and P40, were extracted by dichloromethane from the cell-free supernatant broth and were purified by HPLC. Minimum inhibitory concentrations (MIC) of the compounds were determined against pathogenic and toxigenic microorganisms, most of which are multiresistant to antibiotics. The P40 fraction showed a strong activity especially against Candida albicans, Bacillus subtilis, and Staphylococcus aureus and has lower MIC values than those of P44 against most microorganisms tested. Chemical structures of compounds were determined based on spectroscopic and spectrometric analyses (UV-visible, mass, ¹H, and ¹³C NMR spectra). The compounds P44 and P40 were identified as vineomycin A1 and chaetoglobosin A, respectively. Vineomycin A1 is known to be produced by some Streptomyces species. However, chaetoglobosin A is known to be produced only by fungi belonging to the genera Chaetomium, Penicillium, and Calonectria. This is the first time that chaetoglobosin A, known for its antimicrobial, anticancer, and cytotoxic effects, is reported in prokaryotes.     

Biotechnological potential of a rhizosphere <Emphasis Type="Italic">Pseudomonas</Emphasis><Emphasis Type="Italic">aeruginosa</Emphasis> strain producing phenazine-1-carboxylic acid and phenazine-1-carboxamide

Bacterial phenazine metabolites belong to a group of nitrogen-containing heterocyclic compounds with antimicrobial activities. In this study, a rhizosphere Pseudomonas aeruginosa strain PA1201 was isolated and identified through 16S rDNA sequence analysis and fatty acid profiling. PA1201 inhibited the growth of various pathogenic microorganisms, including Rhizotonia solani, Magnaporthe grisea, Fusarium graminearum, Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicola, and Staphylococcus aureus. High Performance Liquid Chromatography showed that PA1201 produced high levels of phenazine-1-carboxylic acid (PCA), a registered green fungicide ‘Shenqinmycin’ with the fermentation titers of 81.7 mg/L in pigment producing medium (PPM) and 926.9 mg/L in SCG medium containing soybean meal, corn steep liquor and glucose. In addition, PA1201 produced another antifungal metabolite, phenazine-1-carboxaminde (PCN), a derivative of PCA, with the fermentation titers of 18.1 and 489.5 mg/L in PPM and SCG medium respectively. To the best of our knowledge, PA1201 is a rhizosphere originating P. aeruginosa strain that congenitally produces the highest levels of PCA and PCN among currently reported P. aeruginosa isolates, which endows it great biotechnological potential to be transformed to a biopesticide-producing engineering strain.     

Madurastatin B3, a rare aziridine derivative from actinomycete <Emphasis Type="Italic">Nocardiopsis</Emphasis> sp. LS150010 with potent anti-tuberculosis activity

Since the discovery of the first antibiotic, natural products have played an important role in chemistry, biology and medicine. To explore the potential of bioactive compounds from microbes isolated from the southeast of Tibet, China, a crude extract library was constructed and screened against Staphylococcus aureus. The strain Nocardiopsis sp. LS150010 was scaled up and subjected to further chemical studies, resulting in the identification of N-salicyloyl-2-aminopropan-1,3-diol (2) and its rare aziridine derivative, madurastatin B3 (1). Their structures were determined by detailed analysis of 1D, 2D NMR and HRMS data. Compounds 1 and 2 displayed significant inhibitory activity against S. aureus and methicillin resistant S. aureus, with MIC values of 6.25 µg/mL. Compound 1 also showed potent inhibitory activity against Bacillus subtilis and Escherichia coli, as well as activity in a Mycobacterium tuberculosis Bacillus Calmette-Guérin infected THP-1 cell model.     

Use of a mixed culture strategy to isolate halophilic bacteria with antibacterial and cytotoxic activity from the Manaure solar saltern in Colombia

Background

Water evaporation in solar salterns creates salinity gradients that promote the adaptation of microbial species to different salinities. This competitive habitat challenges the metabolic capabilities of microorganisms and promotes alterations in their production of secondary metabolites. Thus, solar salterns are a potentially important source of new natural products. In Colombia, the most important and representative solar saltern is located in Manaure (La Guajira) in the north of Colombia. The aim of this study was to develop an alternative screening strategy to select halophilic bacteria as producers of bioactive compounds from mixed microbial cultures rather than individual environmental isolates. Brine and sediment samples from different ponds (across a salinity gradient) were inoculated in seven different culture media to grow bacteria and archaea, allowing for a total of 40 different mixed cultures. An organic extract from each mixed culture was obtained and tested against multidrug resistant pathogens, including Klebsiella pneumoniae, vancomycin-resistant Enterococcus faecium, methicillin-resistant Staphylococcus aureus and Bacillus subtilis. In addition, the extracts were tested against two human cancer cell lines, cervical adenocarcinoma (SiHa) and lung carcinoma (A-549).

Results

Twenty-four of the forty extracts from mixed cultures obtained from brine and sediment samples from the Manaure solar saltern showed antibacterial activity against Bacillus subtilis. Two extracts, referred to as A1SM3–29 and A1SM3–36, were also active against a methicillin-resistant Staphylococcus aureus, with the latter extract also showing slight cytotoxic activity against the assayed human lung cancer cell line. From this mixed culture, nine isolates were cultivated, and their extracts were tested against the same pathogens, resulting in the identification of a Vibrio sp. strain (A1SM3–36-8) with antimicrobial activity that was similar to that observed for the mixed culture extract. The extract of this strain was subjected to a bioautography assay, and 3 different fractions exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus. Based on the amount obtained for each fraction, F3 was selected to isolate and identify its metabolites. The major compound was identified by NMR and HRMS as 13-cis-docosenamide, an amide that has been previously reported to be an antimicrobial and cytotoxic compound.

Conclusions

Our results shows the utility of our strategy in detecting bioactive molecules in initial mixed cultures by biological assays, resulting in the isolation and characterization of Vibrio sp. A1SM3–36-8, a halophilic strain with great antibacterial and cytotoxic potential.

     

The genus <Emphasis Type="Italic">Diaporthe</Emphasis>: a rich source of diverse and bioactive metabolites

The genus Diaporthe (asexual state: Phomopsis) comprises pathogenic, endophytic and saprobic species with both temperate and tropical distributions. Although species of Diaporthe have in the past chiefly been distinguished based on host association, studies have confirmed several taxa to have wide host ranges, suggesting that they move freely between hosts, frequently co-colonizing diseased or dead tissue, while some species are known to be host-specific. They are also very frequently isolated as endophytes of seed plants. Due to their importance as plant pathogens, the genus has been thoroughly investigated for secondary metabolites, including during screening programs aimed at the discovery of novel bioactive natural products, but the respective information has never been compiled. Therefore, we have examined the relevant literature to explore and highlight the major classes of metabolites of Diaporthe and their Phomopsis conidial states. These fungi predominantly produce a large number of polyketides, but cytochalasins and other types of commonly encountered fungal secondary metabolites are also predominant in some species. Interestingly, not a single metabolite which is also known from the host plant has ever been isolated as a major component from an endophytic Diaporthe strain, despite the fact that many of the recent studies were targeting endophytic fungi of medicinal plants.     

Synthesis and Anti-Infective Activity of 2-Heteroaryl(Acyl)-9,10,12,13-Tetramethoxy-3-Methyl-4,5-Dihydro-3<Emphasis Type="Italic">H</Emphasis>-Phenanthro[1,2-<Emphasis Type="Italic">d</Emphasis>]Azepines

2-Hetaryl- and 2-acyl-9,10,12,13-tetramethoxy-3-methyl-4,5-dihydro-3H-phenanthro[1,2-d]-azepines have been synthesized from 8,9,11,12-tetramethoxy-2-methyl-3,4-dihydronaphtho[2,1-f]isoquinolinium perchlorate by pyridine-azepine recyclization. The resulting compounds have revealed a pronounced antibacterial activity against Staphylococcus aureus (strain P-209) and Escherichia coli (field strain 078). Some of these compounds have a moderate fungistatic activity against Peniciliium italicum fungi. Two compounds have shown a certain activity in relation to the Colpoda steinii protozoa.     

Probiotic Evaluation of Antimicrobial <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> VJC38 Isolated from the Crop of Broiler Chicken

The aim of this study was to evaluate probiotic properties of antimicrobial Lactobacillus plantarum VJC38 in vitro. L. plantarum VJC38 was isolated from the crop of broiler chicken and characterized using dnaK gene sequence. The inhibitory activities of L. plantarum VJC38 against bacterial and fungal pathogens were evaluated. Antifungal compounds secreted by the strain VJC38 were identified using Gas Chromatography and Mass Spectrometry (GC-MS). The strain was evaluated for its tolerance to low pH, resistance to bile salts, auto-aggregation, co-aggregation with pathogenic Escherichia coli, cell surface hydrophobicity, cholesterol lowering activity, β-galactosidase production, adhesion ability to Caco-2 cells, mucin degradation, hemolytic activity and biogenic amine production. Phylogenetic analysis of dnaK gene of bacterial strain VJC38 showed 99% sequence similarity to Lactobacillus plantarum var. plantarum. It showed effective inhibition against food spoiling and pathogenic organisms like Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, Aspergillus niger, Penicillium expansum and Eurotium species. The antifungal compound phenol- 2,4-bis(1,1-dimethylethyl) (PD) was identified in the culture filtrate of L. plantarum VJC38 and reported to have inhibition against Aspergillus species. L. plantarum VJC38 exhibited tolerance to low pH, resistance to bile salts, bile salt hydrolase activity, auto-aggregation (87.5%), co-aggregation with Escherichia coli (55.7%), cholesterol lowering activity (64%), β-galactosidase production (1206 MU), adherence to Caco-2 cells (11%), negative for mucin degradation, hemolytic activity and biogenic amine production. L. plantarum VJC38 could be a good candidate for further investigation in vivo to elucidate its health benefits and to evaluate its technological properties as a bio-protective strain.     

Antimicrobial potential and taxonomic investigation of piezotolerant <Emphasis Type="Italic">Streptomyces</Emphasis> sp. NIOT-Ch-40 isolated from deep-sea sediment

Microbial-derived natural products from extreme niches such as deepsea are known to possess structural and functional novelty. With this background, the present study was designed to investigate the bioprospecting potential and systematics of a deep-sea derived piezotolerant bacterial strain NIOT-Ch-40, showing affiliation to the genus Streptomyces based on 16S RNA gene similarity. Preliminary screening for the presence of biosynthetic genes like polyketide synthase I, polyketide synthase II, non ribosomal peptide synthase, 3-amino-5-hydroxybenzoic acid synthase and spiroindimicin followed by antibacterial activity testing confirmed the presence of potent bioactivity. The secondary metabolites produced during fermentation in Streptomyces broth at 28?°C for 7 days were extracted with ethyl acetate. The extract exhibited a specific inhibitory activity against Gram-positive bacteria and was significantly effective (p?<?0.0001) against methicillin-resistant Staphylococcus aureus (MRSA). The minimum inhibitory concentration and minimum bactericidal concentration against MRSA was 1.5 µg/mL, which was statistically significant in comparison with erythromycin. A multifaceted analysis of the Streptomyces spp. was carried out to delineate the strain NIOT-Ch-40 at a higher resolution which includes morphological, biochemical and molecular studies. Piezotolerance studies and comparison of fatty acid profiles at high pressures revealed that it could be considered as one of the taxonomic markers, especially for the strains isolated from the deep sea environments. In conclusion, the observation of comparative studies with reference strains indicated towards the strain NIOT-Ch-40 as an indigenous marine piezotolerant Streptomyces sp. with a higher probability of obtaining novel bioactive metabolites.     

LyeTx I,a potent antimicrobial peptide from the venom of the spider <Emphasis Type="Italic">Lycosa erythrognatha</Emphasis>

LyeTx I, an antimicrobial peptide isolated from the venom of Lycosa erythrognatha, known as wolf spider, has been synthesised and its structural profile studied by using the CD and NMR techniques. LyeTx I has shown to be active against bacteria (Escherichia coli and Staphylococcus aureus) and fungi (Candida krusei and Cryptococcus neoformans) and able to alter the permeabilisation of l-α-phosphatidylcholine-liposomes (POPC) in a dose-dependent manner. In POPC containing cholesterol or ergosterol, permeabilisation has either decreased about five times or remained unchanged, respectively. These results, along with the observed low haemolytic activity, indicated that antimicrobial membranes, rather than vertebrate membranes seem to be the preferential targets. However, the complexity of biological membranes compared to liposomes must be taken in account. Besides, other membrane components, such as proteins and even specific lipids, cannot be discarded to be important to the preferential action of the LyeTx I to the tested microorganisms. The secondary structure of LyeTx I shows a small random-coil region at the N-terminus followed by an α-helix that reached the amidated C-terminus, which might favour the peptide-membrane interaction. The high activity against bacteria together with the moderate activity against fungi and the low haemolytic activity have indicated LyeTx I as a good prototype for developing new antibiotic peptides.     

Phylogeny,antimicrobial, antioxidant and enzyme-producing potential of fungal endophytes found in <Emphasis Type="Italic">Viola odorata</Emphasis>

Viola odorata, a medicinal plant, is traditionally used to treat common cold, congestion and cough. Given its medicinal properties and occurrence in the northwestern Himalayas, we isolated and characterized endophytic fungi from this plant morphologically, microscopically and by internal transcribed spacer-based rDNA sequencing. In total, we isolated 27 morphotypes of endophytes belonging to phyla Ascomycota and Basidiomycota. The roots showed the highest diversity of endophyte as well as fungal dominance, followed by leaves and leaf nodes. The fungal extract of VOR16 (Fusarium oxysporum) displayed potent antimicrobial activity against Salmonella typhimurium, Klebsiella pneumoniae and Escherichia coli, with a minimum inhibitory concentration of 0.78, 0.78 and 1.56 μg/mL, respectively, while fungal extract VOLF4 (Aspergillus sp.) exhibited promising antioxidant activity (IC₅₀ of 17.4 μg/mL). To identify the components responsible for various bioactivities, we analyzed the content of penicillin G in the extract of bioactive endophytes. The results suggested that the expression of penicillin G under the fermentation conditions applied was too low to display antimicrobial effects. Thus, the activity may be contributed by a different, novel secondary metabolite. The antioxidant activity of VOLF4 may be attributed to its high content of flavonoids. Of the endophytic fungi assessed, 27% were found to be enzyme producers. The highest zone of clearance was observed in VOLN5 (Colletotrichum siamense) for protease production. Only VOR5 (Fusarium nematophilum) was found to be a producer of cellulase, glutenase, amylase and protease. In summary, this is the first report of the isolation of endophytes, namely Fusarium nematophilum, Colletotrichum trifolii, C. destructivum, C. siamense and Peniophora sp., from V. odorata and their bioactive and enzyme-producing potential.     

A look into a multifunctional toolbox: endophytic <Emphasis Type="Italic">Bacillus</Emphasis> species provide broad and underexploited benefits for plants

One of the major challenges of agriculture currently is to obtain higher crop yield. Environmental conditions, cultivar quality, and plant diseases greatly affect plant productivity. On the other hand, several endophytic Bacillus species have emerged as a complementary, efficient, and safe alternative to current crop management practices. The ability of Bacillus species to form spores, which resist adverse conditions, is an advantage of the genus for use in formulations. Endophytic Bacillus species provide plants with a wide range of benefits, including protection against phytopathogenic microorganisms, insects, and nematodes, eliciting resistance, and promoting plant growth, without causing damage to the environment. Bacillus thuringiensis, B. subtilis, B. amyloliquefaciens, B. velezensis, B. cereus, B. pumilus, and B. licheniformis are the most studied Bacillus species for application in agriculture, although other species within the genus have also shown great potential. Due to the increasing number of whole-genome sequenced endophytic Bacillus spp. strains, various bioactive compounds have been predicted. These data reveal endophytic Bacillus species as an underexploited source of novel molecules of biotechnological interest. In this review, we discuss how endophytic Bacillus species are a valuable multifunctional toolbox to be integrated with crop management practices for achieving higher crop yield.     

Purification and characteristics of a novel bacteriocin produced by <Emphasis Type="Italic">Enterococcus faecalis</Emphasis> L11 isolated from Chinese traditional fermented cucumber

Objective

To purify and characterize a novel bacteriocin with broad inhibitory spectrum produced by an isolate of Enterococcus faecalis from Chinese fermented cucumber.

Results

E. faecalis L11 produced a bacteriocin with antimicrobial activity against both Escherichia coli and Staphylococcus aureus. The amino acid sequence of the purified bacteriocin, enterocin L11, was assayed by Edman degradation method. It differs from other class II bacteriocins and exhibited a broad antimicrobial activity against not only Gram-positive bacteria, including Bacillus subtilis, S. aureus, Listeria monocytogenes, Sarcina flava, Lactobacillus acidophilus, L. plantarum, L. delbrueckii subsp. delbrueckii, L. delbrueckii subsp. bulgaricus and Streptococcus thermophilus, but also some Gram-negative bacteria including Salmonella typhimurium, E. coli and Shigella flexneri. Enterocin L11 retained 91 % of its activity after holding at 121 °C for 30 min. It was also resistant to acids and alkalis.

Conclusions

Enterocin L11 is a novel broad-spectrum Class II bacteriocin produced by E. faecalis L11, and may have potential as a food biopreservative.

     

Isolation of <Emphasis Type="Italic">Lactobacillus</Emphasis> strains from shellfish for their potential use as probiotics

Microorganisms intended for use as probiotics in aquaculture should exert antimicrobial activity and be regarded as safe not only for their aquatic hosts but also for their surrounding environments and humans. The objective of this work was to investigate antimicrobial activity against various pathogens, bile salt tolerance, and acid tolerance of 65 presumptive Lactobacillus spp. isolated from shellfish samples. Four strains (HL1, HL12, HL20, and JL28) were selected after qualitatively identifying high levels of antimicrobial activity against bacteria including Staphylococcus aureus, Salmonella typhimurium, Salmonella enteritidis, Escherichia coli O157:H7, Vibrio ichthyoenteri, Edwardsiella tarda, Streptococcus iniae, and V. parahaemolyticus. The sequence analysis of their 16S rRNA genes revealed that the four strains belong to the Lactobacillus plantarum species. In addition, their survivability was tested in bile salt and acidic conditions to show their potential use as probiotics in the gastrointestinal tract.     

Genome analysis reveals insights of the endophytic <Emphasis Type="Italic">Bacillus toyonensis</Emphasis> BAC3151 as a potentially novel agent for biocontrol of plant pathogens

Diseases caused by phytopathogenic microorganisms account for enormous losses for agribusiness. Although Bacillus species are recognized as being antimicrobial producers and some may provide benefits to plants, the association between Bacillus toyonensis and plants has not been studied. In this study, the whole-genome sequenced endophytic B. toyonensis BAC3151, which has demonstrated antimicrobial activity and quorum sensing inhibition of phytopathogenic bacteria, was investigated for its potential for the production of compounds for biocontrol of plant pathogens. Four whole-genome sequenced B. toyonensis strains shared 3811 protein-coding DNA sequences (CDSs), while strain-specific CDSs, such as biosynthetic gene clusters of antimicrobials, were associated with specific chromosomal regions and mobile genetic elements of the strains. B. toyonensis strains had a higher frequency of putative bacteriocins gene clusters than that of Bacillus species traditionally used for the production of antimicrobials. In addition, gene clusters potentially involved in the production of novel bacteriocins were found in BAC3151, as well as biosynthetic genes of several other compounds, including non-ribosomal peptides, N-acyl homoserine lactonase and chitinases, revealing a genetic repertoire for antimicrobial synthesis greater than that of other Bacillus strains that have demonstrated effective activity against phytopathogens. This study showed for the first time that B. toyonensis has potential to produce various antimicrobials, and the analyses performed indicated that the endophytic strain BAC3151 can be useful for the development of new strategies to control microbial diseases in plants that are responsible for large damages in agricultural crops.     

Nematicidal metabolites from <Emphasis Type="Italic">Gliocladium roseum</Emphasis> YMF1.00133

A strain of the fungus Gliocladium roseum YMF1.00133 was found to secrete nematicidal metabolites against nematodes Panagrellus redivivus, Caenothabditis elegans and Bursaphelenchus xylophilus in experiments searching for nematicidal fungi. Through bioassay-guided fractionations, a unique trioxopiperazine alkaloid, gliocladin C (compound 1), and an alkylane resorcinol, 5-n-heneicosylresorcinol (compound 2) were obtained from the methanol extract of the fungus and determined by single-crystal X-ray analysis and spectroscopic data. In vitro immersion experiments showed that the ED₅₀ values of compounds 1 and 2 after 24 h incubation were 15 and 30 μg/mL against C. elegans, 50 and 80 μg/mL against P. redivivus, and 200 and 180 μg/mL against B. xylophilus, respectively. The X-ray diffraction data of compound 1 and the nematicidal activity of compounds 1 and 2 were reported for the first time.     

Eravacycline activity against clinical <Emphasis Type="Italic">S. aureus</Emphasis> isolates from China: in vitro activity,MLST profiles and heteroresistance

Background

Mortality rates for patients with Staphylococcus aureus (S. aureus) infections have improved only modestly in recent decades and S. aureus infections remain a major clinical challenge This study investigated the in vitro antimicrobial activity of erevacycline (erava) against clinical S. aureus isolates from China, as well as the heteroresistance frequency of erava and sequence types (STs) represented in the sample.

Results

A sample of 328 non-duplicate clinical S. aureus isolates, including 138 methecillin-resistant (MRSA) and 190 methecillin-sensitive (MSSA) isolates, were collected retrospectively in China. Erava exhibited excellent in vitro activity (MIC₅₀ ≤?0.25?mg/L) against MRSA and MSSA, including isolates harboring Tet specific resistance genes. The frequency of erava heteroresistance in MSSA with erava MICs?=?0.5?mg/L was 13.79% (4/29); no MRSA with erava MICs ≤0.5?mg/L exhibited heteroresistance. Heteroresistance- derived clones had no 30S ribosome subunit mutations, but their erava MICs (range, 1–4?mg/L) were suppressed dramatically in the presence of efflux protein inhibitors.

Conclusions

Conclusively, erava exhibited excellent in vitro activity against S. aureus, however hints of erava heteroresistance risk and MIC creep were detected, particularly among MSSA with MICs of 0.5?mg/L.

     

Plant growth-promoting potential of endophytic bacteria isolated from roots of wild <Emphasis Type="Italic">Dodonaea viscosa</Emphasis> L.

Dodonaea viscosa, a wild and perennial shrub that can tolerate harsh environmental conditions, was used for the isolation of its endophytic bacteria and their potential was explored for the promotion of Canola growth. The bacteria identified through 16S rRNA gene sequencing, belonged to ten different genera namely Inquilinus, Xanthomonas, Pseudomonas, Rhizobium, Brevundimonas, Microbacterium, Bacillus, Streptomyces, Agrococcus and Stenotrophomonas. All the strains produced small amount of IAA (indole acetic acid) in the absence of tryptophan and comparatively more in the presence of tryptophan. All the bacterial strains were positive for ammonia production, cellulase and pectinase activity, but few of them showed phosphate solubilization, siderophore and hydrogen cyanide production. Only three strains showed ACC (1-aminocyclopropane-1-carboxylate) deaminase activity when tested using in-vitro enzyme assay. Members of genera Bacillus, Pseudomonas and Streptomyces showed positive chitinase, protease and antifungal activity against two phytopathogenic fungi Aspergillus niger and Fusarium oxysoprum, while members of Xanthomonas, Pseudomonas and Bacillus showed significant root elongation of Canola which could be related with their positive plant-growth-promoting (PGP) traits. Among the three plant growth promoting Bacillus strains, B. idriensis is never reported before for its PGP activities. These results showed the potential of Dodonaea viscosa endophytic bacteria as PGPBs, which in future can be further explored for their host range/molecular mechanisms.