Actinobacteria are Gram-positive bacteria with high G+C DNA content that constitute one of the largest bacterial phyla, and they are ubiquitously distributed in both aquatic and terrestrial ecosystems. Many Actinobacteria have a mycelial lifestyle and undergo complex morphological differentiation. They also have an extensive secondary metabolism and produce about two-thirds of all naturally derived antibiotics in current clinical use, as well as many anticancer, anthelmintic, and antifungal compounds. Consequently, these bacteria are of major importance for biotechnology, medicine, and agriculture. Actinobacteria play diverse roles in their associations with various higher organisms, since their members have adopted different lifestyles, and the phylum includes pathogens (notably, species of Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, and Tropheryma), soil inhabitants (e.g., Micromonospora and Streptomyces species), plant commensals (e.g., Frankia spp.), and gastrointestinal commensals (Bifidobacterium spp.). Actinobacteria also play an important role as symbionts and as pathogens in plant-associated microbial communities. This review presents an update on the biology of this important bacterial phylum.

/pdf/taxonomy-physiology-and-natural-products-of-actinobacteria-1arwsidgil.pdf

Taxonomy, Physiology, and Natural Products of Actinobacteria

Introduction: Verticillium spp. are soil-borne plant pathogens responsible for Verticillium wilt diseases in temperate and subtropical regions; collectively they affect over 200 hosts, including many economically important crops. There are currently no fungicides available to cure plants once they are infected. Taxonomy: Kingdom: Fungi, phylum: Ascomycota, subphylum, Pezizomycotina, class: Sordariomycetes, order: Phyllachorales, genus: Verticillium. Host range and disease symptoms: Over 200 mainly dicotyledonous species including herbaceous annuals, perennials and woody species are host to Verticillium diseases. As Verticillium symptoms can vary between hosts, there are no unique symptoms that belong to all plants infected by this fungus. Disease symptoms may comprise wilting, chlorosis, stunting, necrosis and vein clearing. Brown vascular discoloration may be observed in stem tissue cross-sections. Pathogenicity: Verticillium spp. have been reported to produce cell-wall-degrading enzymes and phytotoxins that all have been implicated in symptom development. Nevertheless, evidence for a crucial role of toxins in pathogenicity is inconsistent and therefore not generally accepted. Microsclerotia and melanized mycelium play an important role in the disease cycle as they are a major inoculum source and are the primary long-term survival structures. Resistance: Different defence responses in the prevascular and the vascular stage of Verticillium wilt diseases determine resistance. Although resistance physiology is well established, the molecular processes underlying this physiology remain largely unknown. Resistance against Verticillium largely depends on the isolation of the fungus in contained parts of the xylem tissues followed by subsequent elimination of the fungus. Although genetic resistance has been described in several plant species, only one resistance locus against Verticillium has been cloned to date.

Physiology and molecular aspects of Verticillium wilt diseases caused by V. dahliae and V. albo-atrum.

The actinomycete Streptomyces lydicus WYEC108 showed strong in vitro antagonism against various fungal plant pathogens in plate assays by producing extracellular antifungal metabolites. When Pythium ultimum or Rhizoctonia solani was grown in liquid medium with S. lydicus WYEC108, inhibition of growth of the fungi was observed. When WYEC108 spores or mycelia were used to coat pea seeds, the seeds were protected from invasion by P. ultimum in an oospore-enriched soil. While 100% of uncoated control seeds were infected by P. ultimum within 48 h after planting, less than 40% of coated seeds were infected. When the coated seeds were planted in soil 24 h prior to introduction of the pathogen, 96 h later, less than 30% of the germinating seeds were infected. Plant growth chamber studies were also carried out to test for plant growth effects and for suppression by S. lydicus WYEC108 of Pythium seed rot and root rot. When WYEC108 was applied as a spore-peat moss-sand formulation (10(8) CFU/g) to P. ultimum-infested sterile or nonsterile soil planted with pea and cotton seeds, significant increases in average plant stand, plant length, and plant weight were observed in both cases compared with untreated control plants grown in similar soils. WYEC108 hyphae colonized and were able to migrate downward with the root as it elongated. Over a period of 30 days, the population of WYEC108 colonized emerging roots of germinating seeds and remained stable (10(5) CFU/g) in the rhizosphere, whereas the nonrhizosphere population of WYEC108 declined at least 100-fold (from 10(5) to 10(3) or fewer CFU/g). The stability of the WYEC108 population incubated at 25 degrees C in the formulation, in sterile soil, and in nonsterile soil was also evaluated. In all three environments, the population of WYEC108 maintained its size for 90 days or more. When pea, cotton, and sweet corn seeds were placed into sterile and nonsterile soils containing 10(6) or more CFU of WYEC108 per g, it colonized the emerging roots. After a 1-week growing period, WYEC108 populations of 10(5) CFU/g (wet weight) of root were found on pea roots in the amended sterile soil environment versus 10(4) CFU/g in amended nonsterile soil. To further study the in vitro interaction between the streptomycete and P. ultimum, mycelia of WYEC108 were mixed with oospores of P. ultimum in agar, which was then used as a film to coat slide coverslips.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of streptomyces lydicus WYEC108 as a potential biocontrol agent against fungal root and seed rots.

Publisher Summary There has been a large upsurge in interest in biological disease control recently, reflecting increasing environmental concern over pesticide use. This chapter discusses the ecological considerations, which comprises of suppressive soils, organic amendments and cornposts, monoculture decline, physical and chemical practices, and role of fauna in natural biological disease control. There has been a gradual increase in the number of commercial biocontrol agents on the market for the control of soil–borne plant pathogens over the last few years and only one product, Dagger–G, a Pseudomonaspuorescens marketed by Ecogen, Inc, Lanhorne, PA, USA, for the control of Rhizoctonia and Pythium damping–off of cotton, has been withdrawn from sale because of poor shelf–life of the material. The chapter discusses that chemicals still dominate the disease control market and some consideration should be given to research areas likely to improve further the commercial uptake of biological disease control agents. Consequently, optimizing realistic screening procedures is a first step, which can be refined to target specific types of antagonists. Once specific antagonists have been identified, they can be developed further by consideration of inoculum production, formulation, storage and application, ideally linking the expertise of scientific researchers with industrial partners. Molecular biology has helped identify the modes of action of many biocontrol agents. A considerable effort is currently underway to improve biocontrol efficacy of microorganisms through the use of molecular biology.

Developments in the Biological Control of Soil-borne Plant Pathogens

Among soil microorganisms, bacteria and fungi and to a lesser extent actinomycetes, have received considerable attention as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Within actinomycetes, Streptomyces spp. have been investigated predominantly, mainly because of their dominance on, and the ease of isolation from, dilution plates and because of the commercial interest shown on the antibiotics produced by certain Streptomyces spp. Many of non-streptomycete actinomycetes (NSA) taxa are therefore rarely reported in literature dealing with routine isolations of biocontrol agents and/or plant growth promoters from plant and soil. It is clear that special isolation methods need to be employed in routine isolations to selectively isolate NSA. Some interesting information exists, albeit in relatively few reports compared to that on other microorganisms, on the biological activities of NSA, especially in relation to their mechanisms of action in the biological control of soil-borne fungal plant pathogens and plant growth promotion. This review presents an overview of this information and seeks to encourage further investigations into what may be considered a relatively unexplored area of research. Certain soil environmental factors, especially in horticultural systems, could be manipulated to render the soil conducive for the biological activities of NSA. A variety of NSA isolated by selective methods have not only shown to be rhizosphere competent but also adapted for an endophytic life in root cortices. Some of the NSA, including endophytic strains that have shown potential to suppress soil-borne fungal plant pathogens, are able to employ one or more mechanisms of antagonism including antibiosis, hyperparasitism and the production of cell-wall degrading enzymes. Strains of NSA promote plant growth by producing plant growth regulators. Enhancement of plant growth by the antagonists are considered to help the host by producing compensatory roots that mask the impact of root diseases.

Non-streptomycete actinomycetes as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters

This investigation was designed to explore the potential of microbial antagonism in the control of some tomato diseases including bacterial, Fusarium and Verticillium wilts; early blight; bacterial canker. Three Streptomyces spp. were used: S. pulcher, S. canescens and S. citreofluorescens. The in vitro studies showed that an 80% concentration of the culture filtrate of either S. pulcher or S. canescens significantly inhibited spore germination, mycelial growth and spotulation of Fusarium oxysporum f.sp. lycopersici, Verticillium albo-atrum and Alternaria solani. The same concentration of filtrate of either S. pulcher or S. citreofluorescens was detrimental to the bacterial populations of Clavibacter michiganensis subsp. michiganensis and Pseudomonas solanacearum. The in vivo studies involved different treatments: soaking tomato seeds in filtrate of the antagonist prior to sowing, inoculation of the soil with the antagonist 7 days before sowing, and coating of tomato seeds with spores of the antagonist before sowing. The seed-coating treatment was the most effective in controlling all the pathogens at 42 and 63 days after sowing. Soil inoculation with the antagonist 7 days prior to sowing was less effective in controlling the tomato pathogens as compared to seed-coating. The seed-soaking treatment was the least effective in controlling the diseases concerned. The results also revealed that seed-coating with antagonistic Streptomyces spp. significantly improved tomato growth.

Towards the biological control of fungal and bacterial diseases of tomato using antagonistic Streptomyces spp.

Lake Mariout is Egypt’s degraded coastal marine habitat that encompasses a variety of wastes. The biodiversity and hard environmental conditions allow the co-existence of organisms with high resistance and rich metabolism, making them potential candidates for screening and isolating novel microbial strains. A bacterial isolate (BF202) cultured from the marine sediments of Alexandria’s Mariout Lake (Egypt) was tested for its antimicrobial and anticancer potential. The phylogenetic analysis of the isolated strain’s 16S rDNA and gyrB revealed that BF202 belongs to Brevibacillus laterosporus (B. laterosporus). Antibiosis of B. laterosporus was confirmed against microbial pathogens including Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, and Staphylococcus aureus. The highest antibacterial activity was detected on glucose peptone medium after 18 h of incubation at 35 °C, and at pH of 7.0 in the presence of mannose and ammonium carbonate as carbon and nitrogen sources, respectively. The cytotoxicity of the methanolic extract against breast cancer (MCF-7) and normal Vero cell lines, using the MTT test, revealed IC50 values of 7.93 and 23.79 µg/mL, respectively. To identify apoptotic and necrotic cells, a flow cytometric analysis using annexin V-FITC/PI dual-labeling was utilized and recorded a higher number of necrotic cells compared to apoptotic ones. Similarly, the cell cycle S-phase arrest was reported. The LC-MS-MS investigation of B. laterosporus extract and the molecular networking database analysis demonstrated five strategic diketopiperazine compounds with antimicrobial and anticancer activities. Taken together, this research shows that the crude extract of B. laterosporus might be an effective agent against drug-resistant bacteria and malignant disorders due to its richness in diketopiperazines.

/pdf/structural-diversity-lc-ms-ms-analysis-and-potential-6qwfg1m8.pdf

Structural Diversity, LC-MS-MS Analysis and Potential Biological Activities of Brevibacillus laterosporus Extract

Biocontrol of Aspergillus flavus Producing Aflatoxin B1 by Streptomyces exfoliatus

Over the last few years and with increasing global climatic change, the international energy crisis and shortage of freshwater resources have raised many inquiries about global water security and energy. Therefore, finding out alternative and sustainable energy sources has become an important universal requirement. Here, we assessed the viability of exploiting municipal wastewater (WW) as a nutrient-rich growth medium for cultivating the pollution-tolerant coccoid green microalga Chlorococcum sp. (Chlorophyceae) to simultaneously remove nutrients and produce biodiesel. Chlorococcum sp. was isolated from municipal wastewater sampled from Menoufia Governorate, Egypt. Under the standard growth conditions and until reaching the late exponential growth phase, it was cultivated at different concentrations (25%, 50%, 75%, and 100%) of the secondary treated WW, and the findings were compared to the control (grown in BBM). The study results revealed that the 50% WW treatment was the most suitable approach for removing NO3−, NH4+, and TP with percentages of 96.9%, 98.4%, and 90.1%, respectively. Moreover, the 50% WW treatment produced the highest algal biomass (1.97 g L−1) and productivity (82 mg L−1 day−1). In addition, it showed the highest lipid production (600 mg L−1), with 25 mg L−1 day−1 lipid productivity and lipid yield with 30.5% of the cell dry weight (CDW). The gas chromatography–mass spectrometry (GC-MS) technique was applied to characterize fatty acid profiling, and it was found that oleic (C18:1) and palmitic (C16:0) fatty acids were present in much higher concentrations in Chlorococcum sp. cells grown in 50% WW as compared to the control, i.e., 44.43% and 27.38% vs. 36.75% and 21.36%, respectively. No big difference was present in linoleic (C18:2) fatty acid concentrations. Importantly, the biodiesel properties of our Chlorococcum sp. grown in 50% WW were consistent with the international biodiesel standards. In light of our findings, Chlorococcum sp. has a great potential for utilization as a biodiesel feedstock and for bioremediation of wastewater.

https://www.mdpi.com/2073-4441/15/9/1723/pdf?version=1682694775

Screening the Pollution-Tolerant Chlorococcum sp. (Chlorophyceae) Grown in Municipal Wastewater for Simultaneous Nutrient Removal and Biodiesel Production

Abstract Pollutants cause a huge problem for humans, animals, plants, and various ecosystems, especially water resources. Agricultural, domestic, and industrial waste effluents change the water quality and affect living microorganisms. Therefore, the current study aimed to identify possible microorganisms in wastewater as potential bioremediation agents of pesticide residues. Wastewater samples were collected from El-Khairy agricultural drainage, which receives agricultural and domestic wastes. Bacteria and fungi species were isolated as clean cultures. Wastewater samples were analyzed for pesticide residues via gas chromatography-mass spectroscopy (GC–MS) system. Results uncovered the presence of ten pesticides ranging from 0.0817 to 28.162 µg/l, and the predominant pesticide was chlorpyrifos. Along with that, about nine species (3 bacterial and 6 fungal) were relatively efficient in the removal of chlorpyrifos residues up to 2000 µg/l with removal percentages ranging from 24.16 to 80.93% under laboratory conditions. Two bacterial isolates proficiently degraded significant amounts of chlorpyrifos: Bacillus cereus strain PC2 (GenBank accession No. MZ314010) and Streptomyces praecox strain SP1 (GenBank accession No. MZ314009). In-site bacterial and fungal isolates defined in the current study were proficient in cleaning wastewater of chlorpyrifos pesticide residues. 

/pdf/bioremediation-of-chlorpyrifos-residues-using-some-2mng1wcy.pdf

Sabha M. El-Sabbagh

Papers

Towards the biological control of fungal and bacterial diseases of tomato using antagonistic Streptomyces spp.

Structural Diversity, LC-MS-MS Analysis and Potential Biological Activities of Brevibacillus laterosporus Extract

Biocontrol of Aspergillus flavus Producing Aflatoxin B1 by Streptomyces exfoliatus

Screening the Pollution-Tolerant Chlorococcum sp. (Chlorophyceae) Grown in Municipal Wastewater for Simultaneous Nutrient Removal and Biodiesel Production

Bioremediation of chlorpyrifos residues using some indigenous species of bacteria and fungi in wastewater