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Abstract A better understanding of the genetic regulation of the biosynthesis of microbial compounds could accelerate the discovery of new biologically active molecules and facilitate their production. To this end, we have investigated the time course of genome‐wide transcription in the myxobacterium Sorangium sp. So ce836 in relation to its production of natural compounds. Time‐resolved RNA sequencing revealed that core biosynthesis genes from 48 biosynthetic gene clusters (BGCs; 92% of all BGCs encoded in the genome) were actively transcribed at specific time points in a batch culture. The majority (80%) of polyketide synthase and non‐ribosomal peptide synthetase genes displayed distinct peaks of transcription during exponential bacterial growth. Strikingly, these bursts in BGC transcriptional activity were associated with surges in the net production rates of known natural compounds, indicating that their biosynthesis was critically regulated at the transcriptional level. In contrast, BGC read counts from single time points had limited predictive value about biosynthetic activity, since transcription levels varied >100‐fold among BGCs with detected natural products. Taken together, our time‐course data provide unique insights into the dynamics of natural compound biosynthesis and its regulation in a wild‐type myxobacterium, challenging the commonly cited notion of preferential BGC expression under nutrient‐limited conditions. The close association observed between BGC transcription and compound production warrants additional efforts to develop genetic engineering tools for boosting compound yields from myxobacterial producer strains.

A wide range of bioactive compounds with potential medical applications are produced by members of the genus Streptomyces. A new actinomycete producer of the antibiotic γ-rubromycin, designated TA 36, was isolated from an alpine soil sample collected in Peru (Machu Picchu). Morphological, physiological and biochemical characteristics of the strain, together with data obtained via phylogenetic analysis and MALDI-TOF MS, were used for the correct identification of the isolate. The isolate TA 36 showed morphological characteristics that were consistent with its classification within the genus Streptomyces. Phylogenetic analysis based on 16S rRNA gene sequences showed that the TA 36 strain was most similar to S. iakyrus and S. violaceochromogenes with 99% similarity. Phylogenetic analysis together with the profile of whole cell proteins indicated that the strain tested could be identified as S. iakyrus TA 36. The crude extract Ext.5333.TA 36 showed various effects against the tested organisms with strong antimicrobial activity in the growth of Staphylococcus aureus (Newman) (MIC value of 0.00195 µg/µL). HPLC fractionation and LC/MS analysis of the crude extract led to the identification of the quinone antibiotic γ-rubromycin, a promising antitumour and antibacterial antibiotic. To the best of our knowledge, there is currently no report on the production of γ-rubromycin by S. iakyrus. Therefore, this study suggests S. iakyrus TA 36 as the first-reported source of this unique bioactive secondary metabolite.

Background and Objectives: DNA extraction is an important step of any molecular experiment. DNA could not be easily extracted from members of actinomycetes by the usual methods of lysis. Due to the low efficiency of the conventional DNA extraction methods, development of an effective technique for DNA extraction of actinobacteria in emergency cases seems to be necessary. Since most of the DNA extraction techniques and commercial kits are not efficient enough to extract DNA from actinobacteria, this study was conducted to improve an efficient method obtained from conventional one to extract DNA from this group of bacteria. Materials and Methods: DNA extraction was performed using five methods (an improved method, Invisorb Spin Plant Mini Kit, EZ-10 Spin Column, Sarrbrucken method (HZI, Germany) and Kirby Bauer's method). To evaluate the quantity and quality of extracted genomic DNA, UV absorbance of all samples and efficiency of polymerase chain reaction (PCR) were evaluated. Results: Overall, the results revealed that the highest quantity (up to 4000 ng/µl) and good quality of DNA was obtained using introduced DNA extraction method. Conclusion: Results indicated that recently introduced improved method was more efficient for extraction of DNA from actinobacteria for DDH (DNA–DNA hybridization) test and for those require the high concentration of DNA.

The discovery of new antibiotic is needed, due to the increasing antimicrobial resistance in nature. Therefore, this study aims to isolate gliding bacteria and to ascertain their antimicrobial activity against pathogenic microbes. This research was conducted by isolating gliding bacteria from mangrove sediment in Muara Angke, North Jakarta, Indonesia. All of the strains were identified by 16S rRNA genes sequencing and those selected strain was characterized using polyphasic approach. The performance of crude extracts against to ten pathogenic microorganisms were detected using serial dilution test in 96-well plates. Mangrove gliding bacteria isolates designated 313MSO and 314MSO were showed high homology to Ohtaekwangia kribbensis with 96.20% and 99.12% similarity, respectively. The polyphasic approach led to the conclusion that the strain 313MSO was a new species of the genus Ohtaekwangia. Twenty-three crude extracts were obtained from cultivating the strain in twenty-three different media. The most of them inhibited the growth of Staphylococcus aureus Newman with the minimum concentration of 33.33-66.67 µg/ml. Four compounds (Marinoquinolines A-D) were obtained from HPLC-MS analysis. Furthermore, the strain 313MSO is presently being studied for in-depth identification of additional unknown metabolites detected in the crude extracts.

Introduction: Myxobacteria are Gram-negative Deltaproteobacteria with rod-shaped vegetative cells, aerobic organotrophs that exhibit unique group behavior. Materials and Methods:The myxobacterial strain Mx18Zk was isolated from intestinal tract of earth worm of GhaemshahrCounty in Mazandaranprovince and the extraction of the fermented broth culture was prepared with organic solvent extraction method. Methanol extract tested for potential antimicrobial activity against11 various human pathogens. Finally the rest of methanol extract fractionated by HPLC and tested again against sensitive pathogens. Results: Strain Mx18Zk significantly inhibited growth of Escherichia coli, Staphylococcus aureus and Chromobacterium violaceum, therefore was used for further characterization. Analysis of morphological, biochemical, 16S rRNA gene sequence and phylogenetic tree indicated that this strain with 100 % homology belongs to the genus Corallococcus macrosporus . The methanol extract was subjected to HPLC fractionation against sensitive pathogens. The active extracts studied by LC-MS and its results compared by previously identified myxobacterial secondary metabolites deposited in Myxobase database of HZI. LC/MS analysis resulted in the identification of Myxochromids and unknown Myxovirescins, Myxalamides antibiotics in methanol extract of the strain Mx18Zk. Discussion and conclusion: On the basis of results, isolated strain was active against Escherichia coli, Staphylococcus aureus and Chromobacterium violaceum and100 % homology was belong to the genus Corallococcus macrosporus. LC/MS analysis resulted in the identification of Myxochromids and unknown Myxovirescins, Myxalamides antibiotics in methanol extract of the strain Mx18Zk.

The discovery of novel secondary metabolites is actively being pursued in new ecosystems. Sponge-associated bacteria have been in the limelight in recent years on account of their ability to produce bioactive compounds. In this study, heterotrophic bacteria associated with four sponge species were isolated, taxonomically identified, and subjected to screening for the production of bioactive entities against a panel of nine microorganisms, including Gram-positive and negative bacteria, as well as yeast and fungi. Of the 105 isolated strains, 66% were represented by Proteobacteria, 16% by Bacteriodetes, 7% by Actinobacteria, and 11% by Firmicutes. Bioactivity screening revealed that 40% of the total isolated strains showed antimicrobial activity against one or more of the target microorganisms tested. Further, active extracts from selective species were narrowed down by bioassay-guided fractionation and subsequently identified by HR-ESI-MS analyses to locate the active peaks. Presumably responsible compounds for the observed bioactivities were identified as pentadecenoic acid, oleic acid, and palmitoleic acid. One isolate, Qipengyuania pacifica NZ-96T, based on 16S rRNA novelty, was subjected to comparative metabolic reconstruction analysis with its closest phylogenetic neighbors, revealing 79 unique functional roles in the novel isolate. In addition, genome mining of Qipengyuania pacifica NZ-96T revealed three biosynthetic gene clusters responsible for the biosynthesis of terpene, beta lactone, lasso peptide, and hserlactone secondary metabolites. Our results demonstrate the ability to target the sponge microbiome as a potential source of novel microbial life with biotechnological potential.

A novel myxobacterial strain ZKHCc1 1396T was isolated in 2017 from a soil sample collected along Chalus Road connecting Tehran and Mazandaran, Iran. It was a Gram-negative, rod-shaped bacterial strain that displayed the general features of Corallococcus, including gliding and fruiting body formation on agar and microbial lytic activity. Strain ZKHCc1 1396T was characterized as an aerobic, mesophilic, and chemoheterotrophic bacterium resistant to many antibiotics. The major cellular fatty acids were branched-chain iso-C17:0 2-OH, iso-C15:0, iso-C17:1, and iso-C17:0. The strain showed the highest 16S rRNA gene sequence similarity to Corallococcusterminator CA054AT (99.67%) and C. praedator CA031BT (99.17%), and formed a novel branch both in the 16S rRNA gene sequence and phylogenomic tree. The genome size was 9,437,609 bp, with a DNA G + C content of 69.8 mol%. The strain had an average nucleotide identity (ANI) value lower than the species cut-off (95%), and with the digital DNA–DNA hybridization (dDDH) below the 70% threshold compared to the closest type strains. Secondary metabolite and biosynthetic gene cluster analyses revealed the strain’s potential to produce novel compounds. Based on polyphasic taxonomic characterization, we propose that strain ZKHCc1 1396T represents a novel species, Corallococcus soli sp. nov. (NCCB 100659T = CIP 111634T).

Actinobacteria isolated from untapped environments and exposed to extreme conditions such as saltpans are a promising source of novel bioactive compounds. These microorganisms can provide new molecules through either the biosynthetic pathway or the biotransformation of organic molecules. In the present study, we performed a chemical metabolic screening of secondary metabolites secreted by the new strain CG3, which was isolated from a saltpan located in the Sahara of Algeria, via high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-ESI-HRMS). The results indicated that this strain produced five new polyene macrolactams, kenalactams A–E, along with two known compounds, mitomycin C and 6″-hydroxy-4,2′,3′,4″ tetramethoxy-p-terphenyl. Furthermore, the CG3 isolate could have excellent properties for converting the aglycone isoflavone glycitein to the compounds 6,7-dimethoxy-3-(4-methoxyphenyl)chromen-4-one (50) and 6,7-dimethoxy-3-phenylchromen-4-one (54), and the isoflavone genistein can be converted to 5,7-dimethoxy-3-(4-methoxyphenyl)chromen-4-one (52). Docking studies and molecular dynamics simulations indicated that these three isoflavones, generated via biotransformation, are potent inhibitors of the target protein aromatase (CYP19A1); consequently, they can be used to prevent breast cancer risk in postmenopausal women.

A marine Alphaproteobacterium designated as strain NZ-96T was isolated in February 2021, from a sponge species (Demospongiae) collected in muddy sediments with boulders and old chimneys in Otago/Canterbury Slope, Pacific Ocean, New Zealand. The isolate was found to be Gram-negative, rod-shaped, aerobic, motile, and produced yellow-colored colonies. The isolate was positive for alkaline phosphatase, leucine arylamidase, trypsin, catalase, and oxidase and negative for α-galactosidase and urease. It was resistant to many antibiotics including hygromycin, trimethoprim, spectinomycin, ampicillin, oxytetracycline, cephalosporin, bacitracin, and polymyxin. The 16S rRNA gene-based phylogenetic analyses exhibited that strain NZ-96T belonged to the genus Qipengyuania and showed 98.3–98.8% 16S rRNA gene sequence similarity to its closest relatives. The major respiratory quinone was ubiquinone-10 (Q-10). The polar lipid profile consisted of phosphatidylcholine, sphingoglycolipid, phosphatidylglycerol, one unknown polar lipid, and three unknown glycolipids. The major fatty acids were C18:1ω12t, C16:0, C16:1ω7c, C17:1ω6c, C16:02-OH, and C14:0 2-OH. Carotenoid were produced. The crude extract showed pronounced activity against Staphylococcus aureus Newman and Bacillus subtilis DSM 10. Pairwise ANI and dDDH values of strain NZ-96T and closely related phylogenetic hits were below the threshold values of 95% and 70%, respectively. Genes for trehalose biosynthesis, aspartate-semialdehyde dehydrogenase, flagellar biosynthesis, fatty acid biosynthesis, and antibiotics resistance were present, which aids in isolate survival in a sea or ocean environment. The DNA G+C content was 60.8% (by genome). Based on data obtained by the polyphasic approach, strain NZ-96T (= DSM 112811T = NCCB 100842T) represents a novel species of the genus Qipengyuania, for which the name Qipengyuania pacifica sp. nov. is proposed.

A yellow bacterium from marine agar, strain WHA3T, was isolated from the mantel of the Pacific oysters Crassostrea gigas in the Wilhelmshaven Sea in northern Germany. Based on the 16S rRNA gene sequence, strain WHA3T had a high similarity to Pacificimonas flava JLT2015T (95.80%) and 94.79% to Pacificimonas aurantium JLT2012T. Furthermore, the dDDH and ANI value analysis between WHA3T and other closest type strains were lower than 70% and 95%, respectively. The percentage of conserved proteins (POCP) and the average amino acid identity (AAI) value against Pacificimonas flava JLT2015T and Pacificimonas aurantium JLT2012T represented in the ranges of higher than 50% and 60%, respectively. Strain WHA3T contained ubiquinone-10 (Q-10) as the predominant quinone, and the major fatty acids were C16:1 ω7c and C18:1 ω7c. Granules of polyhydroxyalkanoates (PHAs) were absent. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, several sphingoglycolipids, an unknown phospholipid, an unknown glycolipid, and an unknown polar lipid. The polyamines contained spermidine and spermine. The DNA G + C content of strain WHA3T was 61.69%. An analysis of the whole-genome sequence in the frame of genome mining strain WHA3T predicted the presence of genomes for one-carbon metabolism, TonB-dependent transporters, vitamin B12 transporter, iron siderophore receptor protein, and other genes, some of which play important roles against restricted nutrient sources. The extract of strain WHA3T moderately inhibited the growth of Candida albicans DSM 1665. The polyphasic taxonomic analysis results suggested that strain WHA3T could be separated from its closest type strains. Strain WHA3T represents a novel species in the genus Pacificimonas, for which we propose the name Pacificimonaspallium sp. nov., with the type strain WHA3T (= DSM 111825T = NCCB 100832T).

Lanyamycin (1/2), a secondary metabolite occurring as two epimers, was isolated from the myxobacterium Sorangium cellulosum, strain Soce 481. The structures of both epimers were elucidated from HRESIMS and 1D and 2D NMR data and the relative configuration of their macrolactone ring was assigned based on NOE and vicinal 1H NMR coupling constants and by calculation of a 3D model. Lanyamycin inhibited HCV infection into mammalian liver cells with an IC50 value of 11.8 µM, and exhibited a moderate cytotoxic activity against the mouse fibroblast cell line L929 and the human nasopharyngeal cell line KB3 with IC50 values of 3.1 and 1.5 μM, respectively, and also suppressed the growth of the Gram-positive bacterium Micrococcus luteus.

A novel Gram-negative, aerobic, motile, lemon-yellow-colored, and non-spore-forming rod-shaped bacterium designated strain NZ-12BT was isolated in February 2021 from a sponge species (Crateromorpha) collected at the southern Kermadec Ridge, Pacific Ocean, New Zealand. Comparative 16S rRNA gene-based analyses indicated that strain NZ-12BT shared 98.58%, 96.44%, 96.23%, and 94.78% 16S rRNA sequence similarity to Alteriqipengyuania lutimaris S-5T, Qipengyuania pelagi UST081027-248T, Qipengyuania citreus RE35F/1T, and Alteriqipengyuania halimionae CPA5T, respectively. The major respiratory quinone was ubiquinone-10(Q-10). The polar lipid profile of NZ-12BT was composed of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidyl-N-methyl-ethanolamine, phosphatidylcholine, sphingoglycolipid, phosphatidylglycerol, one unknown polar lipid, three unknown phospholipids, and three unknown glycolipids. The major fatty acids of strain NZ-12BT were C18:1ω12t, C16:0, C17:1ω6c, and C14:02-OH. Carotenoids were present. Genome mining analysis revealed a biosynthetic gene cluster encoding for the terpene biosynthesis. Pairwise ANI and dDDH values of strain NZ-12BT and closely related phylogenetic neighbors were below the threshold values of 95% and 70%, respectively. The DNA G+C content was 65.4 mol% (by genome). Based on data obtained by a polyphasic approach, type strain NZ-12BT (=DSM 112810T = NCCB 100841T) represents a novel species of the genus Alteriqipengyuania, for which the name Alteriqipengyuania abyssalis sp. nov. is proposed.

Here, we describe the polyphasic taxonomy of a novel isolated strain WH53T from the genus Zooshikella isolated from the sand sediment located between the lumen of the Crassostrea gigas From Germany. Phylogenetic analysis determined that the strain WH53T had a high similarity to Zooshikella ganghwensis JC2044T (99.57%) and Zooshikella marina LMG 28823T (99.36%). Strain WH53T contained ubiquinone-9 (Q-9) as the predominant menaquinone, and the major fatty acids were C16:0, C16:1ω7c, and C18:1ω7c. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, amino phospholipids, and unidentified phospholipids were identified as their polar lipid composition. The DNA G+C content and genome size of strain WH53T were 40.08 mol% and 5,914,969 bp, respectively. Digital DNA–DNA hybridisation (dDDH) for strain WH53T against Z. ganghwensis JC2044T and Z. marina LMG 28823T showed low relatedness values of 26.3% and 26.1%, respectively. The extract of strain WH53T exhibited antimicrobial property. Strain WH53T represents a novel species in the genus Zooshikella. We propose the name of Zooshikella harenae sp. nov., with the type strain WH53T (= DSM 111628T = NCCB 100808T). Furthermore, the dDDH, average nucleotide identity (ANI), percentage of conserved proteins (POCP), and amino acid identity (AAI) value between Z. marina LGM 28823T and Z. ganghwensis DSM 15267T were 79.9%, 97.84%, 76.08%, and 87.01%, respectively, suggesting that both of them should be reclassified as Z. ganghwensis subsp. marina subsp. nov. and Z. ganghwensis subsp. ganghwensis DSM 15267 subsp. nov.

Two known Polybrominated Diphenyl Ethers (PBDEs), 3,4,5-tribromo-2-(2′,4′-dibromophenoxy)phenol (1d) and 3,4,5,6-tetrabromo-2-(2′,4′-dibromophenoxy)phenol (2b), were isolated from the Indonesian marine sponge Lamellodysidea herbacea. The structure was confirmed using 13C chemical shift average deviation and was compared to the predicted structures and recorded chemical shifts in previous studies. We found a wide range of bioactivities from the organic crude extract, such as (1) a strong deterrence against the generalist pufferfish Canthigaster solandri, (2) potent inhibition against environmental and human pathogenic bacterial and fungal strains, and (3) the inhibition of the Hepatitis C Virus (HCV). The addition of a bromine atom into the A-ring of compound 2b resulted in higher fish feeding deterrence compared to compound 1d. On the contrary, compound 2b showed only more potent inhibition against the Gram-negative bacteria Rhodotorula glutinis (MIC 2.1 μg/mL), while compound 1d showed more powerful inhibition against the other human pathogenic bacteria and fungi. The first report of a chemical defense by compounds 1d and 2b against fish feeding and environmental relevant bacteria, especially pathogenic bacteria, might be one reason for the widespread occurrence of the shallow water sponge Lamellodysidea herbacea in Indonesia and the Indo-Pacific.

The rare actinobacterium Amycolatopsis sp. strain 195334CR was found to produce previously undescribed cyclic hexapeptides, which we named amycolatomycin A and B (1 and 2). Their planar structures were determined by high-resolution mass spectrometry as well as extensive 1D and 2D NMR spectroscopy, while the absolute stereochemistry of its amino acids were determined by Marfey’s method. Moreover, 1 and 2 differ by the incorporation of l-Ile and l-allo-Ile, respectively, whose FDVA (Nα-(2,4-Dinitro-5-fluorphenyl)-L-valinamide) derivatives were separated on a C4 column. Their hallmark in common is a unique 2,6-dichloro-tryptophan amino acid unit. Amycolatomycin A (1) exhibited weak activity against Bacillus subtilis DSM 10 (minimum inhibitory concentration (MIC) = 33.4 µg/mL).

The manuscript investigated the isolation, characterization and anti-infective potential of valinomycin (3), streptodepsipeptide P11A (2), streptodepsipeptide P11B (1), and one novel valinomycin analogue, streptodepsipeptide SV21 (4), which were all produced by the Gram-positive strain Streptomycescavourensis SV 21. Although the exact molecular weight and major molecular fragments were recently reported for compound 4, its structure elucidation was not based on compound isolation and spectroscopic techniques. We successfully isolated and elucidated the structure based on the MS2 fragmentation pathways as well as 1H and 13C NMR spectra and found that the previously reported structure of compound 4 differs from our analysis. Our findings showed the importance of isolation and structure elucidation of bacterial compounds in the era of fast omics technologies. The here performed anti-infective assays showed moderate to potent activity against fungi, multi drug resistant (MDR) bacteria and infectivity of the Hepatitis C Virus (HCV). While compounds 2, 3 and 4 revealed potent antiviral activity, the observed minor cytotoxicity needs further investigation. Furthermore, the here performed anti-infective assays disclosed that the symmetry of the valinomycin molecule is most important for its bioactivity, a fact that has not been reported so far.

Antibiotic producers have mainly been isolated from soil, which often has led to the rediscovery of known compounds. In this study, we identified the freshwater snail Physa acuta as an unexplored source for new antibiotic producers. The bacterial diversity associated with the snail was characterized by a metagenomic approach using cultivation-independent high-throughput sequencing. Although Actinobacteria represented only 2% of the bacterial community, the focus was laid on the isolation of the genus Streptomyces due to its potential to produce antibiotics. Three Streptomyces strains (7NS1, 7NS2 and 7NS3) were isolated from P. acuta, and the antimicrobial activity of the crude extracts were tested against a selection of Gram-positive and Gram-negative bacteria and fungi. 7NS3 showed the strongest activity against Gram-positive bacteria and, thus, was selected for genome sequencing and a phylogenomic analysis. 7NS3 represents a novel Streptomyces species, which was deposited as Streptomyces sp. DSM 110735 at the Leibniz Institute-German Collection of Microorganisms and Cell Cultures (DSMZ). Bioassay-guided high-performance liquid chromatography (HPLC) and high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS) analyses of crude extract fractions resulted in the detection of four compounds, one of which matched the compound characteristics of emycin A, an angucycline-like aromatic polyketide. Genome mining studies based on the whole-genome sequence of 7NS3 resulted in the identification of a gene cluster potentially coding for emycin A biosynthesis. Our study demonstrates that freshwater snails like P. acuta can represent promising reservoirs for the isolation of new antibiotic-producing actinobacterial species.

The history of our antibiotics is inseparably connected to microorganisms as producers [...]

Streptomonospora sp. M2 has been isolated from a soil sample collected at the Wadden Sea beach in our ongoing program aimed at the isolation of rare Actinobacteria, ultimately targeting the discovery of new antibiotics. Because crude extracts derived from cultures of this strain showed inhibitory activity against the indicator organism Bacillus subtilis, it was selected for further analysis. HPLC–MS analysis of its culture broth revealed the presence of lipophilic metabolites. The two major metabolites of those were isolated by preparative reversed-phase HPLC and preparative TLC. Their planar structures were elucidated using high-resolution electrospray ionization mass spectrometry (HRESIMS), 1D and 2D NMR data as new thiopeptide antibiotics and named litoralimycin A (1) and B (2). Although rotating frame nuclear Overhauser effect spectroscopy (ROESY) data established a Z configuration of the Δ21,26 double bond, the stereochemistry of C-5 and C-15 were assigned as S by Marfey’s method after ozonolysis. The biological activity spectrum of 1 and 2 is highly uncommon for thiopeptide antibiotics, since they showed only insignificant antibacterial activity, but 1 showed strong cytotoxic effects.

During the course of our ongoing screening for novel biologically active secondary metabolites, the rare Actinobacterium, Nonomuraea sp. 1808210CR was found to produce five unprecedented β-carboline derivatives, nonocarbolines A−E (1−5). Their structures were elucidated from high-resolution mass spectrometry, 1D and 2D nuclear magnetic resonance spectroscopy, and the absolute configuration of 4 was determined by using the modified Mosher method. Nonocarboline B (2) displayed moderate antifungal activity against Mucor hiemalis, while nonocarboline D (4) exhibited significant cytotoxic activity against the human lung carcinoma cell line A-549 with the IC50 value of 1.7 µM.

The search for novel bioactive metabolites continues to be of much importance around the world for pharmaceutical, agricultural, and industrial applications. Actinobacteria constitute one of the extremely interesting groups of microorganisms widely used as important biological contributors for a wide range of novel secondary metabolites. This study focused on the assessment of antimicrobial and antioxidant activity of crude extracts of actinobacterial strains. Western Ghats of India represents unique regions of biologically diverse areas called “hot spots”. A total of 32 isolates were obtained from soil samples of different forest locations of Bisle Ghat and Virjapet situated in Western Ghats of Karnataka, India. The isolates were identified as species of Streptomyces, Nocardiopsis, and Nocardioides by cultural, morphological, and molecular studies. Based on preliminary screening, seven isolates were chosen for metabolites extraction and to determine antimicrobial activity qualitatively (disc diffusion method) and quantitatively (micro dilution method) and scavenging activity against DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals. Crude extracts of all seven isolates exhibited fairly strong antibacterial activity towards MRSA strains (MRSA ATCC 33591, MRSA ATCC NR-46071, and MRSA ATCC 46171) with MIC varying from 15.62 to 125 μg/mL, whereas showed less inhibition potential towards Gram-negative bacteria Salmonella typhi (ATCC 25241) and Escherichia coli (ATCC 11775) with MIC of 125−500 μg/mL. The isolates namely S1A, SS5, SCA35, and SCA 11 inhibited Fusarium moniliforme (MTCC 6576) to a maximum extent with MIC ranging from 62.5 to 250 μg/mL. Crude extract of SCA 11 and SCA 13 exhibited potent scavenging activities against DPPH and ABTS radicals. The results from this study suggest that actinobacterial strains of Western Ghats are an excellent source of natural antimicrobial and antioxidant compounds. Further research investigations on purification, recovery, and structural characterization of the active compounds are to be carried out.

In order to minimize re-discovery of already known anti-infective compounds, we focused our screening approach on understudied, almost untapped marine environments including marine invertebrates and their associated bacteria. Therefore, two sea cucumber species, Holothuria leucospilota and Stichopus vastus, were collected from Lampung (Indonesia), and 127 bacterial strains were identified by partial 16S rRNA-gene sequencing analysis and compared with the NCBI database. In addition, the overall bacterial diversity from tissue samples of the sea cucumbers H. leucospilota and S. vastus was analyzed using the cultivation-independent Illumina MiSEQ analysis. Selected bacterial isolates were grown to high densities and the extracted biomass was tested against a selection of bacteria and fungi as well as the hepatitis C virus (HCV). Identification of putative bioactive bacterial-derived compounds were performed by analyzing the accurate mass of the precursor/parent ions (MS1) as well as product/daughter ions (MS2) using high resolution mass spectrometry (HRMS) analysis of all active fractions. With this attempt we were able to identify 23 putatively known and two previously unidentified precursor ions. Moreover, through 16S rRNA-gene sequencing we were able to identify putatively novel bacterial species from the phyla Actinobacteria, Proteobacteria and also Firmicutes. Our findings suggest that sea cucumbers like H. leucospilota and S. vastus are promising sources for the isolation of novel bacterial species that produce compounds with potentially high biotechnological potential.

Polyketides are a large group of secondary metabolites that have notable variety in their structure and function. Polyketides exhibit a wide range of bioactivities such as antibacterial, antifungal, anticancer, antiviral, immune-suppressing, anti-cholesterol, and anti-inflammatory activity. Naturally, they are found in bacteria, fungi, plants, protists, insects, mollusks, and sponges. Streptomyces is a genus of Gram-positive bacteria that has a filamentous form like fungi. This genus is best known as one of the polyketides producers. Some examples of polyketides produced by Streptomyces are rapamycin, oleandomycin, actinorhodin, daunorubicin, and caprazamycin. Biosynthesis of polyketides involves a group of enzyme activities called polyketide synthases (PKSs). There are three types of PKSs (type I, type II, and type III) in Streptomyces responsible for producing polyketides. This paper focuses on the biosynthesis of polyketides in Streptomyces with three structurally-different types of PKSs.

Planctomycetes are conspicuous, ubiquitous, environmentally important bacteria. They can attach to various surfaces in aquatic habitats and form biofilms. Their unique FtsZ-independent budding cell division mechanism is associated with slow growth and doubling times from six hours up to one month. Despite this putative disadvantage in the struggle to colonize surfaces, Planctomycetes are frequently associated with aquatic phototrophic organisms such as diatoms, cyanobacteria or kelp, whereby Planctomycetes can account for up to 50 % of the biofilm-forming bacterial population. Consequently, Planctomycetes were postulated to play an important role in carbon utilization, for example as scavengers after phototrophic blooms. However, given their observed slow growth, such findings are surprising since other faster- growing heterotrophs tend to colonize similar ecological niches. Accordingly, Planctomycetes were suspected to produce antibiotics for habitat protection in response to the attachment on phototrophs. Recently, we demonstrated their genomic potential to produce nonribosomal peptides, polyketides, bacteriocins, and terpenoids that might have antibiotic activities. In this study, we describe the development of a pipeline that consists of tools and procedures to cultivate Planctomycetes for the production of antimicrobial compounds in a chemically- defined medium and a procedure to chemically mimic their interaction with bacteria such as for example Cyanobacteria. We evaluated and adjusted screening assays to allow the hunt for planctomycetal antibiotics. As proof of principle, we demonstrate antimicrobial activities of planctomycetal extracts from Planctopirus limnophila DSM 3776, Rhodopirellula baltica DSM 10527, and the recently isolated strain Pan216. By combining UV/Vis and high resolution mass spectrometry data from High-Performance Liquid Chromatography fractionations with growth inhibition of indicator strains, we were able to assign the antibiotic activity to candidate peaks related to planctomycetal antimicrobial compounds. The MS analysis points towards the production of novel bioactive molecules with novel structures. Consequently, we developed a large scale cultivation procedure to allow future structural elucidation of such compounds.Our findings might have implications for the discovery of novel antibiotics as Planctomycetes represent a yet untapped resource that could be developed by employing the tools and methods described in this study.

Two new secondary metabolites, labindole A [2-methyl-3-(2-nitroethyl)-3H-indole] (1) and labindole B [2-methyl-3-(2-nitrovinyl)-3H-indole] (2), were isolated from the myxobacterium Labilithrix luteola (DSM 27648T). Additionally, four metabolites 3, 4, 5 and 6 already known from other sources were obtained. Their structures were elucidated from high resolution electrospray ionisation mass spectrometry (HRESIMS) and 1D and 2D nuclear magnetic resonance (NMR) spectroscopy data and their relative configuration was assigned based on nuclear Overhauser effect (NOE) and vicinal 1H-NMR coupling data. The compounds where tested for biological activities; labindoles A (1) and B (2) exhibited significant activity against Hepatitis C Virus, 9H-carbazole (3), 3-chloro-9H-carbazole (4) and 4-hydroxymethyl-quinoline (5) showed antifungal activities. Moreover, compound 3 had weak to moderate antibacterial activities, while labindoles A (1) and B (2) were devoid of significant antifungal and antibacterial effects.

ABSTRACT The strain no. VY46 was isolated from agricultural soil of Slovak republic and tested for potential antimicrobial activity against various human pathogens. On the basis of results, strain VY46 significantly inhibited growth of yeast Candida albicans and therefore was used for further characterization. In order to explore the potential bioactivities, extract of the fermented broth culture was prepared with organic solvent extraction method. The ethylacetate extract was subjected to HPLC fractionation against Candida albicans and followed by LC/MS analysis for potential production of anticandidal substances. The analysis resulted in the identification of two antimycins antibiotics, which may be responsible for important anticandidal activity of the strain. On the basis of liquid chromatography and mass spectrometry the antibiotics were identified as Urauchimycin A and Kitamycin A. According tothe results from cultural, morphological, physiological, biochemical and 16S rRNA gene sequence methods, the strain was identified as Streptomyces albidoflavus. In addition, neighbor-joining phylogenetic tree confirmed the relationships of this strain to other members of Streptomyces genera.