In the present study we reported the antimicrobial activity of actinomycetes isolated from aridic soil sample collected in Karoo, South Africa. Eighty-six actinomycete strains were isolated and purified, out of them thirty-four morphologically different strains were tested for antimicrobial activity. Among 35 isolates, 10 (28.57%) showed both antibacterial and antifungal activity. The ethyl acetate extract of strain KRG-1 showed the strongest antimicrobial activity and therefore was selected for further investigation. The almost complete nucleotide sequence of the 16S rRNA gene as well as distinctive matrix-assisted laser desorption/ionization-time-of-flight/mass spectrometry (MALDI-TOF/MS) profile of whole-cell proteins acquired for strain KRG-1 led to the identification of Streptomyces antibioticus KRG-1 (GenBank accession number: KX827270). The ethyl acetate extract of KRG-1 was fractionated by HPLC method against the most suppressed bacterium Staphylococcus aureus (Newman). LC//MS analysis led to the identification of the active peak that exhibited UV-VIS maxima at 442 nm and the ESI-HRMS spectrum showing the prominent ion clusters for [M-H 2 O+H] + at m/z 635.3109 and for [M+Na] + at m/z 1269.6148. This information could be assigned to chromopeptide lactone antibiotic-actinomycin. Our results suggest that unexplored soils could be an interesting source for exploring antibacterial secondary metabolites.

No abstract

Fifty seven soil-borne actinomycete strains were assessed for the antibiotic production. Two of the most active isolates, designed as Streptomyces ST-13 and DK-15 exhibited a broad range of antimicrobial activity and therefore they were selected for HPLC fractionation against the most suppressed bacteria Staphylococcus aureus (ST-13) and Chromobacterium violaceum (DK-15). LC/MS analysis of extracts showed the presence of polyketides factumycin (DK15) and tetrangomycin (ST13). The taxonomic position of the antibiotic-producing actinomycetes was determined using a polyphasic approach. Phenotypic characterization and 16S rRNA gene sequence analysis of the isolates matched those described for members of the genus Streptomyces. DK-15 strain exhibited the highest 16S rRNA gene sequence similarity to Streptomyces globosus DSM-40815 (T) and Streptomyces toxytricini DSM-40178 (T) and ST-13 strain to Streptomyces ederensis DSM-40741 (T) and Streptomyces phaeochromogenes DSM-40073 (T). For the proper identification, MALDI-TOF/MS profile of whole-cell proteins led to the identification of S. globosus DK-15 (accession number: KX527570) and S. ederensis ST13 (accession number: KX527568). To our knowledge, there is no report about the production of these antibiotics by S.globosus and S. ederensis, thus isolates DK15 and ST13 identified as S. globosus DK-15 and S.ederensis ST-13 can be considered as new sources of these unique antibacterial metabolites.

In laboratory assay, the diversity of bacteria and microscopic fungi and the community-level physiological profiling (CLPP) of microorganisms were observed after the addition of bio-sludge (40 t.ha-1) from a biogas station and addition of bio-fertlizers-AZOTER (10 dm-3 .ha-1) to the arable soil with PCR-DGGE and BIOLOG ® method (Eco Plates). The differences were recorded in the microbial diversity (bacteria and microscopic fungi) among variants according to the Shannon index. The differences in community of microscopic fungi were markedly higher among the soil samples with the additions of both bio-fertilizers compared to control soil samples. The occurrence of individual OTUs (operational taxonomic units) bacteria and microscopic fungi were different after 105 days of incubation from the status after the 1 st day of incubation. The community metabolic diversity (CMD) was influenced by the incubation time (105 days) as well, but not by application of bio-fertilizers. We observed a significant decrease (LSD test, P <0.05) in community metabolic diversity (CMD) and average metabolic response (AMR) of microorganisms in samples collected on the 105 th day of the experiment compared to samples collected on the 1 st day of the experiment in all tested samples.

The main objective of this study was using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for assembling of DSM (German Collection of Microorganisms) Streptomyces spectral database and identification of wild Streptomyces cultures, which were clustered by MALDI-TOF Biotyper OC software as well as for teracycline detection by observing of obtained spectra using flexAnalysis software. Production of tetracycline was confirmed by thin-layer chromatography. Presence of tetracycline mass spectrum was verified by several tetracycline producers (Streptomyces aureofaciens LMG 5968, S. aureofaciens 84/25, and S. aureofaciens BMK) and by pure tetracycline mass. Our results showed that it is possible to use MALDI-TOF MS for identification of tetracycline producers within Streptomyces genera by several easy steps. The purpose of this study was to establish cheap and quick detection of tetracycline producers.

Bread is considered an intermediate - moisture food product that is prone to mould spoilage. Growth of spoilage fungi is currently controlled with the addition of chemical preservatives. Consumers demand more natural products and there is a need to reduce the amount of chemical preservatives added to foods. Essential oils (EOs) and their constituents emerged as promising and effective compounds to protect foods from lipid peroxidation and provide microbiological food safety. So the aim of our study was to determinate microscopic fungi involved in contamination of bread target the genus Eurotium and to evaluate the antifungal activity of 5 EOs by vapor contact against the fungal species of this genus. In all samples after three days of cultivation fungi created colonies on the surface of the crust and the pieces of the bread samples stored on DRBC were after three days of cultivation covered with fungi colonies. Altogether 195 isolates were recovered from 8 bread samples and assigned to 10 fungal genera. The most frequently genus of fungi was Penicillium, Aspergillus, Cladosporium, Epicoccum and Eurotium. Based on phylogenetic and morphological studies, five different Eurotium species were identified: E. amstelodami, E. chevalieri, E. herbariorum, E. rubrum and E. repens. In this study, we explored the potential of five essential oils retrieved from some Lamiaceae species, concretely: basil (Ocinum basilicum L.), lavender (Lavandula angustifolia Mill.), oregano (Origanum vulgare L.), mint (Metha piperita L.) and sage (Salvia officinalis L.). Gas chromatography–mass spectrometry (GC-MS) analysis allowed for the identification of 28 compounds as main constituents. Inhibitory activity of EOs was assessed against 5 species of genus Eurotium (2 isolates for each specie). In all studied strains, the essential oils caused significant differences (Pbasil (with the best Mycelial growth Inhibition (MGI) 93.65% to E. herbariorum) and the low effect had sage essential oil (with the best MGI 68.62% to E. repens). The present study demonstrated the potential food preservative ability of essential oils from some Lamiaceae species.

Myxobacteria, a group of antimicrobial producing bacteria, have been successfully cultured and characterized from 10 soil samples collected from different parts of Slovakia. A total of 79 myxobacteria belonging to 4 genera (Myxococcus, Corallococcus, Sorangium, and Polyangium) were isolated based aspects on of their life cycle. Twenty five of them were purified, fermented, and screened for antimicrobial activities against 11 test microorganisms. Results indicated that crude extracts showed more significant activities against Gram-positive than against Gram-negative bacteria or fungi. Based on a higher degree and broader range of antimicrobial production, the two most potential extracts (K9-5, V3-1) were selected for HPLC fractionation against Micrococcus luteus and Staphylococcus aureus and LC/MS analysis of potential antibiotic metabolites. The analysis resulted in the identification of polyketide-peptide antibiotics, namely corallopyronin A and B (K9-5) and myxalamid B and C (V3-1), which were responsible for important Gram-positive activity in the observed strains. A sequence similarity search through BLAST revealed that these strains showed the highest sequence similarity to Corallococcus coralloides (K9-5, NCBI accession number KX256198) and Myxococcus xanthus (V3-1, NCBI accession number KX256197). Although screening of myxobacteria is laborious, due to difficulties in isolating cultures, this research represented the first report covering the isolation and cultivation of this challenging bacterial group from Slovakian soils as well as the screening of their antimicrobial activity, cultural identification, and secondary metabolite identification.

ABSTRACT