Repertoire and abundance of secreted virulence factors shape the pathogenic capacity of Pseudomonas syringae pv. aptata.

Pseudomonas syringae pv. aptata is a member of the sugar beet pathobiome and the causative agent of leaf spot disease. Like many pathogenic bacteria, P. syringae relies on the secretion of toxins, which manipulate host-pathogen interactions, to establish and maintain an infection. This study analyzes the secretome of six pathogenic P. syringae pv. aptata strains with different defined virulence capacities in order to identify common and strain-specific features, and correlate the secretome with disease outcome. All strains show a high type III secretion system (T3SS) and type VI secretion system (T6SS) activity under apoplast-like conditions mimicking the infection. Surprisingly, we found that low pathogenic strains show a higher secretion of most T3SS substrates, whereas a distinct subgroup of four effectors was exclusively secreted in medium and high pathogenic strains. Similarly, we detected two T6SS secretion patterns: while one set of proteins was highly secreted in all strains, another subset consisting of known T6SS substrates and previously uncharacterized proteins was exclusively secreted in medium and high virulence strains. Taken together, our data show that P. syringae pathogenicity is correlated with the repertoire and fine-tuning of effector secretion and indicate distinct strategies for establishing virulence of P. syringae pv. aptata in plants.

Culture-Dependent and Metabarcoding Characterization of the Sugar Beet (Beta vulgaris L.) Microbiome for High-Yield Isolation of Bacteria with Plant Growth-Promoting Traits.

The diversity of plant-associated bacteria is vast and can be determined by 16S rRNA gene metabarcoding. Fewer of them have plant-beneficial properties. To harness their benefits for plants, we must isolate them. This study aimed to check whether 16S rRNA gene metabarcoding has predictive power in identifying the majority of known bacteria with plant-beneficial traits that can be isolated from the sugar beet (Beta vulgaris L.) microbiome. Rhizosphere and phyllosphere samples collected during one season at different stages of plant development were analyzed. Bacteria were isolated on rich unselective media and plant-based media enriched with sugar beet leaves or rhizosphere extracts. The isolates were identified by sequencing the 16S rRNA gene and tested in vitro for their plant-beneficial properties (stimulation of germination; exopolysaccharide, siderophore, and HCN production; phosphate solubilization; and activity against sugar beet pathogens). The highest number of co-occurring beneficial traits was eight, found in isolates of five species: Acinetobacter calcoaceticus, Bacillus australimaris, B. pumilus, Enterobacter ludwiigi, and Pantoea ananatis. These species were not detected by metabarcoding and have not previously been described as plant-beneficial inhabitants of sugar beets. Thus, our findings point out the necessity of a culture-dependent microbiome analysis and advocate for low-nutrient plant-based media for high-yield isolation of plant-beneficial taxa with multiple beneficial traits. A culture-dependent and -independent approach is required for community diversity assessment. Still, isolation on plant-based media is the best approach to select isolates for potential use as biofertilizers and biopesticides in sugar beet cultivation.

Genome Analysis of Two Pseudomonas syringae pv. aptata Strains with Different Virulence Capacity Isolated from Sugar Beet: Features of Successful Pathogenicity in the Phyllosphere Microbiome.

Members of the Pseudomonas syringae species complex are heterogeneous bacteria that are the most abundant bacterial plant pathogens in the plant phyllosphere, with strong abilities to exist on and infect different plant hosts and survive in/outside agroecosystems. In this study, the draft genome sequences of two pathogenic P. syringae pv. aptata strains with different in planta virulence capacities isolated from the phyllosphere of infected sugar beet were analyzed to evaluate putative features of survival strategies and to determine the pathogenic potential of the strains. The draft genomes of P. syringae pv. aptata strains P16 and P21 are 5,974,057 bp and 6,353,752 bp in size, have GC contents of 59.03% and 58.77%, respectively, and contain 3,439 and 3,536 protein-coding sequences, respectively. For both average nucleotide identity and pangenome analysis, P16 and P21 largely clustered with other pv. aptata strains from the same isolation source. We found differences in the repertoire of effectors of the type III secretion system among all 102 selected strains, suggesting that the type III secretion system is a critical factor in the different virulent phenotypes of P. syringae pv. aptata. During genome analysis of the highly virulent strain P21, we discovered genes for T3SS effectors (AvrRpm1, HopAW1, and HopAU1) that were not previously found in genomes of P. syringae pv. aptata. We also identified coding sequences for pantothenate kinase, VapC endonuclease, phospholipase, and pectate lyase in both genomes, which may represent novel effectors of the type III secretion system. IMPORTANCE Genome analysis has an enormous effect on understanding the life strategies of plant pathogens. Comparing similarities with pathogens involved in other epidemics could elucidate the pathogen life cycle when a new outbreak happens. This study represents the first in-depth genome analysis of Pseudomonas syringae pv. aptata, the causative agent of leaf spot disease of sugar beet. Despite the increasing number of disease reports in recent years worldwide, there is still a lack of information about the genomic features, epidemiology, and pathogenic life strategies of this particular pathogen. Our findings provide advances in disease etiology (especially T3SS effector repertoire) and elucidate the role of environmental adaptations required for prevalence in the pathobiome of the sugar beet. From the perspective of the very heterogeneous P. syringae species complex, this type of analysis has specific importance in reporting the characteristics of individual strains.

Genotyping-driven diversity assessment of biocontrol potent Bacillus spp. strain collection as a potential method for the development of strain-specific biomarkers.

Bacillus species are among the most researched and frequently applied biocontrol agents. To estimate their potential as environmentally friendly microbial-based products, reliable and rapid plant colonization monitoring methods are essential. We evaluated repetitive element-based (rep) and Random Amplified Polymorphic DNA (RAPD) PCR (Polymerase Chain Reaction) genotyping in a diversity assessment of 251 strains from bulk soil, straw, and manure samples across Serbia, highlighting their discriminative force and the presence of unique bands. RAPD 272, OPG 5, and (GTG)5 primers were most potent in revealing the high diversity of a sizable environmental Bacillus spp. collection. RAPD 272 also amplified a unique band for a proven biocontrol strain, opening the possibility of Sequence Characterized Amplified Region (SCAR) marker design. That will enable colonization studies using the SCAR marker for its specific detection. This study provides a guide for primer selection for diversity and monitoring studies of environmental Bacillus spp. isolates.

Bacteriobiota and Chemical Changes during the Ripening of Traditional Fermented "Pirot 'Ironed' Sausage".

"Pirot 'ironed' sausage" (Pis) is a traditional, fermented sausage, made from different types of meat (beef and chevon), without additives or starter cultures. The physical-chemical properties (pH, water activity, fats, moisture, and protein contents) were examined in the initial meat batter stuffing and during ripening. Total bacterial diversity was examined at different time points using both culturable (traditional) and non-culturable (NGS sequencing) approaches. During the ripening, a decrease in pH value, aw, and moisture content was observed, as well as an increase in protein and fat content. At least a two-fold significant decrease was noted for colorimetric values during the ripening period. The dominance of Proteobacteria and Firmicutes was observed in the non-culturable approach in all studied samples. During the ripening process, an increase in Firmicutes (from 33.5% to 63.5%) with a decrease in Proteobacteria (from 65.4% to 22.3%) was observed. The bacterial genera that were dominant throughout the ripening process were Lactobacillus, Photobacterium, Leuconostoc, Weissella, and Lactococcus, while Carnobacterium, Brochothrix, and Acinetobacter were found also, but in negligible abundance. Among the culturable bacteria, Latilactobacillus sakei (Lactobacillus sakei) and Leuconostoc mesenteoides were present in all stages of ripening.

The Microbiome of the 'Williams' Pear Variety Grown in the Organic Orchard and Antifungal Activity by the Autochthonous Bacterial and Yeast Isolates.

The total diversity of bacterial and fungal communities associated with the phyllosphere (fruits and leaves) of the 'Williams' pear variety was analyzed in two phenological stages during fruit development and maturation. The antagonistic potential of autochthonous bacterial and yeast isolates against phytopathogenic fungi was also evaluated. A metabarcoding approach revealed Pantoea, Sphingomonas, Hymenobacter, Massilia, and Pseudomonas as dominant bacterial constituents of the pear phyllosphere, whilst most abundant among the fungal representatives identified were Metschnikowia, Filobasidium, Aureobasidiumpullulans, Botrytis cinerea, and Taphrina. The traditional culturable approach revealed that the Pseudomonas genus with P. graminis, P. putida, and P. congelans was most prevalent. The most frequently cultivated fungal representatives belonged to the genus Fusarium with six identified species. A broad range of the antagonistic activity was detected for the Hannaella luteola and Metschnikowia pulcherrima yeasts, significantly affecting the growth of many fungal isolates in the range of 53-70%. Fusarium sporotrichioides was the most susceptible fungal isolate. The autochthonous antagonistic yeasts H. luteola and M. pulcherrima might be powerful biological control agents of postharvest diseases caused by Fusarium spp. and common pathogens like Monilinia laxa, Botrytis cinerea, Alternaria tenuissima, and Cladosporium cladosporioides.

Phyllosphere Fungal Communities of Plum and Antifungal Activity of Indigenous Phenazine-Producing Pseudomonas synxantha Against Monilinia laxa.

European plum (Prunus domestica L.) is a significant commercial crop in Serbia in terms of total fruit production, and is traditionally processed into slivovitz brandy. The brown rot disease caused by Monilinia laxa drastically reduces plum yield almost every year. Fungal communities associated with leaves and fruits of four local Serbian plum cultivars (Pozegaca, Ranka, Cacanska Lepotica and Cacanska Rodna) were investigated in two phenological stages during early (May) and late (July) fruit maturation. Alpha diversity indices showed that fungal communities were heterogeneous and Beta diversity indicated that autochthonous fungal communities depended upon seasonal changes and the cultivars themselves. The phylum Ascomycota was the most abundant in all samples, with relative abundance (RA) between 46% in the Pozegaca cultivar (May) and 89% in the Lepotica cultivar (July). The most abundant genus for all plum cultivars in May was Aureobasidium, with RA from 19.27 to 33.69%, followed by Cryptococcus, with 4.8 to 48.80%. In July, besides Cryptococcus, different genera (Metschnikowia, Fusarium, and Hanseniaspora) were dominant on particular cultivars. Among all cultivable fungi, molecular identification of eleven M. laxa isolates from four plum cultivars was performed simultaneously. Bacterial isolates from the plum phyllosphere were tested for their potential antifungal activity against indigenous M. laxa isolates. The most potent antagonist P4/16_1, which significantly reduced mycelial growth of M. laxa, was identified as Pseudomonas synxantha. Further characterization of P4/16_1 revealed the production of volatile organic compounds and phenazine-1-carboxylic acid (PCA). Crude benzene extract of PCA exhibited 57-63% mycelial growth inhibition of M. laxa. LC/MS analysis of the crude extract confirmed the presence of phenazine derivatives amongst other compounds. Scanning electron microscopy revealed morpho-physiological changes in the hyphae of M. laxa isolates caused by the cell culture and the P. synxantha P4/16_1 crude benzene extract. This is the first report of antagonistic activity of P. synxantha against M. laxa induced by diffusible and volatile antifungal compounds, and it appears to be a promising candidate for further investigation for potential use as a biocontrol agent against brown rot-causing fungi.

Biological control of plant pathogens by Bacillus species.

Bacteria from the Bacillus group are microorganisms that inhabit a large number of different habitats. They are well known as producers of a wide array of antagonistic compounds of different structures, having between 5 to 8% of the total genome devoted to biosynthesis of secondary metabolites. Most important bioactive molecules from the genus Bacillus are non-ribosomally synthesized peptides and lipopeptides, polyketide compounds, bacteriocins and siderophores. Lipopeptides from Bacillus have very complex mechanisms of biosynthesis catalyzed by non-ribosomal peptide synthetases (NRPSs), large enzyme complexes with modular structure, with each module being in charge for the incorporation of a particular amino acid. In general, they have a broad spectrum of antagonistic activity against plant pathogenic bacteria, fungi and viruses. Most important molecules from this group, circular lipopeptides from surfactin, iturin and fengycin families affect the target cells on the membrane level. Bacillus strains exhibit their biocontrol capacity predominantly through inhibitory activity on the growth of plant pathogens, as well as inducing systemic resistance in plants and competing for ecological niches with plant pathogens. Our previous studies showed the presence of multiple biosynthetic operons for synthesis of non-ribosomal lipopeptides in the collection of natural isolates of Bacillus, with many strains having more than one of them. Several strains of Bacillus sp. that we have recently characterized showed very strong antibacterial and antifungal activity against phytopathogens. The PCR analysis showed the presence of biosynthetic operons for iturin, bacillomycin, fengycin and surfactin in tested strains. Measurement of the kinetics of production of antimicrobial substances showed that, in most cases, synthesis started at the beginning of exponential phase of growth, reaching the maximum of antimicrobial activity at the beginning of the stationary growth phase and stayed at this level for the whole duration of observed period. Preparations of cell-free supernatants of tested strains were active against many fungal and bacterial pathogens, in vitro and in vivo. Mass spectrometry and HPTLC bioautography analysis of purified compounds confirmed the presence of lipopeptides of mentioned families, hence confirming the biocontrol capacity of Bacillus isolates.

A contribution to pharmaceutical biology of freshwater sponges.

In vitro anti-tumour and anti-radical activities of the acetone extract of the freshwater sponge Ochridaspongia rotunda were the subject of this study. The extract was found to be highly cytotoxic to human lung tumour cell line A-549 reaching IC50 value of 5.01 ± 0.21 µg/mL. Indeed, it displayed only 2-fold less anti-tumour activity than doxorubicin (IC50 value 2.42 ± 0.13 µg/mL) used as a positive control. The same extract was also found to be almost 37-fold more selective against A-549 vs. MRC-5 (normal) lung cells, in difference to weak selectivity of doxorubicin (less than 3-fold). Its profound anti-DPPH radical activity comparable to that of quercetin (IC50 values 3.68 ± 0.19 and 3.14 ± 0.09 µg/mL, respectively) coupled with no signs of genotoxicity in the comet assay (MRC-5 cell line, vs. doxorubicin) has actually implicated the importance of this animal bioresource in searching for pharmaceutically useful bioactive compounds of natural origin.

Corrigendum: The Profile and Antimicrobial Activity of Bacillus Lipopeptide Extracts of Five Potential Biocontrol Strains.

[This corrects the article on p. 925 in vol. 8, PMID: 28588570.].

The Profile and Antimicrobial Activity of Bacillus Lipopeptide Extracts of Five Potential Biocontrol Strains.

In this study the efficacy of two different methods for extracting lipopeptides produced by five Bacillus strains-ethyl acetate extraction, and acid precipitation followed by methanol extraction-was investigated using mass spectrometry. High performance thin layer chromatography (HPTLC) was also used for the simultaneous separation of complex mixtures of lipopeptide extracts and for the determination of antimicrobial activity of their components. The mass spectra clearly showed well-resolved groups of peaks corresponding to different lipopeptide families (kurstakins, iturins, surfactins, and fengycins). The ethyl acetate extracts produced the most favorable results. The extracts of SS-12.6, SS-13.1, and SS-38.4 showed the highest inhibition zones. An iturin analog is responsible for the inhibition of Xanthomonas arboricola and Pseudomonas syringae phytopathogenic strains. HPTLC bioautography effectively identified the active compounds from a mixture of lipopeptide extracts, proving in situ its potential for use in direct detection and determination of antimicrobials. In the test of potential synergism among individual extracts used in different mixtures, stronger antimicrobial effects were not observed. Biochemical and phylogenetic analysis clustered isolates SS-12.6, SS-13.1, SS-27.2, and SS-38.4 together with Bacillus amyloliquefaciens, while SS-10.7 was more closely related to Bacillus pumilus.

Further insight into the bioactivity of the freshwater sponge Ochridaspongia rotunda.

CONTEXT: Bioprospection has become a dynamic scientific field that explores novel possibilities for the implementation of natural products in medicine and pharmacy. Compared to marine species from all kingdoms, freshwater species have been highly neglected. OBJECTIVE: This work focuses on the screening of acetylcholinesterase inhibitory (AChE) and mutagenic activities of the acetone extract (obtained by maceration) of the freshwater sponge Ochridaspongia rotunda Arndt (Malawispongiidae) in vitro. MATERIALS AND METHODS: AChE inhibitory activity was evaluated both in liquid (five different concentrations of the extract, from 1 to 100 µg/mL) and in solid (seven different concentrations of the extract, from 0.5 to 10.0 µg) by methods well described in literature, while mutagenicity was estimated using the Ames test (four different concentrations of the extract, from 0.106 to 1.328 mg/plate). RESULTS: Ochridaspongia rotunda acetone extract exhibited promising AChE inhibitory activity in a dose-dependent manner both in liquid (IC50 23.07 µg/mL) and in solid (1.50 µg). Furthermore, the Ames test revealed no sign of mutagenicity at any concentration tested. Its FTIR spectrum coupled with the positive Liebermann?Burchard, Salkowski and Zak color reactions (tests) indicated the presence of sterol compounds. DISCUSSION AND CONCLUSION: The screened extract may inspire a search for novel anticholinesterase therapeutic agent(s) potentially used in the treatment of Alzheimer's disease. Further research will be directed toward its detailed chemical analysis along with addressing the issue of a real producer of the natural product(s) responsible for the AChE activity observed.

Licheniocin 50.2 and Bacteriocins from Lactococcus lactis subsp. lactis biovar. diacetylactis BGBU1-4 Inhibit Biofilms of Coagulase Negative Staphylococci and Listeria monocytogenes Clinical Isolates.

BACKGROUND: Coagulase negative staphylococci (CoNS) and Listeria monocytogenes have important roles in pathogenesis of various genital tract infections and fatal foetomaternal infections, respectively. The aim of our study was to investigate the inhibitory effects of two novel bacteriocins on biofilms of CoNS and L. monocytogenes genital isolates. METHODS: The effects of licheniocin 50.2 from Bacillus licheniformis VPS50.2 and crude extract of bacteriocins produced by Lactococcus lactis subsp. lactis biovar. diacetylactis BGBU1-4 (BGBU1-4 crude extract) were evaluated on biofilm formation and formed biofilms of eight CoNS (four S. epidermidis, two S. hominis, one S. lugdunensis and one S. haemolyticus) and 12 L. monocytogenes genital isolates. RESULTS: Licheniocin 50.2 and BGBU1-4 crude extract inhibited the growth of both CoNS and L. monocytogenes isolates, with MIC values in the range between 200-400 AU/ml for licheniocin 50.2 and 400-3200 AU/ml for BGBU1-4 crude extract. Subinhibitory concentrations (1/2 × and 1/4 × MIC) of licheniocin 50.2 inhibited biofilm formation by all CoNS isolates (p < 0.05, respectively), while BGBU1-4 crude extract inhibited biofilm formation by all L. monocytogenes isolates (p < 0.01 and p < 0.05, respectively). Both bacteriocins in concentrations of 100 AU/mL and 200 AU/mL reduced the amount of 24 h old CoNS and L. monocytogenes biofilms (p < 0.05, p < 0.01, p < 0.001). CONCLUSIONS: This study suggests that novel bacteriocins have potential to be used for genital application, to prevent biofilm formation and/or to eradicate formed biofilms, and consequently reduce genital and neonatal infections by CoNS and L. monocytogenes.

Antimicrobial Activity of Serbian Propolis Evaluated by Means of MIC, HPTLC, Bioautography and Chemometrics.

New information has come to light about the biological activity of propolis and the quality of natural products which requires a rapid and reliable assessment method such as High Performance Thin-Layer Chromatography (HPTLC) fingerprinting. This study investigates chromatographic and chemometric approaches for determining the antimicrobial activity of propolis of Serbian origin against various bacterial species. A linear multivariate calibration technique, using Partial Least Squares, was used to extract the relevant information from the chromatographic fingerprints, i.e. to indicate peaks which represent phenolic compounds that are potentially responsible for the antimicrobial capacity of the samples. In addition, direct bioautography was performed to localize the antibacterial activity on chromatograms. The biological activity of the propolis samples against various bacterial species was determined by a minimum inhibitory concentration assay, confirming their affiliation with the European poplar type of propolis and revealing the existence of two types (blue and orange) according to botanical origin. The strongest antibacterial activity was exhibited by sample 26 against Staphylococcus aureus, with a MIC value of 0.5 mg/mL, and Listeria monocytogenes, with a MIC as low as 0.1 mg/mL, which was also the lowest effective concentration observed in our study. Generally, the orange type of propolis shows higher antimicrobial activity compared to the blue type. PLS modelling was performed on the HPTLC data set and the resulting models might qualitatively indicate compounds that play an important role in the activity exhibited by the propolis samples. The most relevant peaks influencing the antimicrobial activity of propolis against all bacterial strains were phenolic compounds at RF values of 0.37, 0.40, 0.45, 0.51, 0.60 and 0.70. The knowledge gained through this study could be important for attributing the antimicrobial activity of propolis to specific chemical compounds, as well as the verification of HPTLC fingerprinting as a reliable method for the identification of compounds that are potentially responsible for antimicrobial activity. This is the first report on the activity of Serbian propolis as determined by several combined methods, including the modelling of antimicrobial activity by HPTLC fingerprinting.

Protective effect of basil (Ocimum basilicum L.) against oxidative DNA damage and mutagenesis.

Mutagenic and antimutagenic properties of essential oil (EO) of basil and its major constituent Linalool, reported to possess antioxidative properties, were examined in microbial tests. In Salmonella/microsome and Escherichia. coli WP2 reversion assays both derivatives (0.25-2.0 microl/plate) showed no mutagenic effect. Salmonella. typhimurium TA98, TA100 and TA102 strains displayed similar sensitivity to both basil derivatives as non-permeable E. coli WP2 strains IC185 and IC202 oxyR. Moreover, the toxicity of basil derivatives to WP2 strains did not depend on OxyR function. The reduction of t-BOOH-induced mutagenesis by EO and Linalool (30-60%) was obtained in repair proficient strains of the E. coli K12 assay (Nikolic, B., Stanojevic, J., Mitic, D., Vukovic-Gacic, B., Knezevic-Vukcevic, J., Simic, D., 2004. Comparative study of the antimutagenic potential of vitamin E in different E. coli strains. Mutat. Res. 564, 31-38), as well as in E. coli WP2 IC202 strain. EO and Linalool reduced spontaneous mutagenesis in mismatch repair deficient E. coli K12 strains (27-44%). In all tests, antimutagenic effect of basil derivatives was comparable with that obtained with model antioxidant vitamin E. Linalool and vitamin E induced DNA strand breaks in Comet assay on S. cerevisiae 3A cells, but at non-genotoxic concentrations (0.075 and 0.025 microg/ml, respectively) they reduced the number of H(2)O(2)-induced comets (45-70% Linalool and 80-93% vitamin E). Obtained results indicate that antigenotoxic potential of basil derivatives could be attributed to their antioxidative properties.