Indigenous actinomycetes from empty fruit bunch compost of oil palm: Evaluation on enzymatic and antagonistic properties

Changes in the microbiota during biological treatment of palm oil mill waste: A critical review

Palm oil mill waste has a complex cellulosic structure, is rich in nutrients, and provides a habitat for diverse microbial communities. Current research focuses on how the microbiota and organic components interact during the degradation of this type of waste. Some recent studies have described the microbial communities present in different biodegradation processes of palm oil mill waste, identifying the dominant bacteria/fungi responsible for breaking down the cellulosic components. However, understanding the degradation process's mechanisms is vital to eliminating the need for further pretreatment of lignocellulosic compounds in the waste mixture and facilitating the commercialization of palm oil mill waste treatment technology. Thus, the present work aims to review microbial community dynamics via three biological treatment systems comprehensively: composting, vermicomposting, and dark fermentation, to understand how inspiration from nature can further enhance existing degradation processes. The information presented could be used as an umbrella to current research on biological treatment processes and specific research on the bioaugmentation of indigenous microbial consortia isolated during the biological degradation of palm oil mill waste.

Streptomyces sennicomposti sp. nov., an actinomycete isolated from compost of Senna siamea (Lam.)

A member of the genus Streptomyces , designated RCPT1-4T, was isolated from compost of Senna siamea (Lam.), collected from an agricultural area in Rayong province, Thailand. The spore morphology and the presence of ll-diaminopimelic acid in the peptidoglycan indicate that RCPT1-4T shows the typical properties of members of the genus Streptomyces . On the basis of the results of 16S rRNA gene sequence analysis, the strain should be classified as representing a member of the genus Streptomyces and was most closely related to Streptomyces fumigatiscleroticus NBRC 12999T with the highest 16S rRNA gene sequence similarity of 99.2 %, followed by Streptomyces spiralis NBRC 14215T (99.0 %). In addition, RCPT1-4T shared the highest average nucleotide identity by blast (ANIb) (86.0 %), and digital DNA–DNA hybridization (dDDH) (32.1 %) values with S. spiralis NBRC 14215T. Furthermore, several physiological and biochemical differences were observed between RCPT1-4T and the closely related type strains of species with validly published names. These taxonomic data indicated that RCPT1-4T could be considered to represent a novel species of the genus Streptomyces and the name Streptomyces sennicomposti sp. nov. is proposed for this strain. The type strain is RCPT1-4T (=TBRC 11260T=NBRC 114303T).

Current strategies and perspectives in detection and control of basal stem rot of oil palm

The rapid expansion of oil palm (OP) has led to its emergence as a commodity of strategic global importance. Palm oil is used extensively in food and as a precursor for biodiesel. The oil generates export earnings and bolsters the economy of many countries, particularly Indonesia and Malaysia. However, oil palms are prone to basal stem rot (BSR) caused by Ganoderma boninense which is the most threatening disease of OP. The current control measures for BSR management including cultural practices, mechanical and chemical treatment have not proved satisfactory. Alternative control measures to overcome the G. boninense problem are focused on the use of biological control agents and many potential bioagents were identified with little proven practical application. Planting OP varieties resistant to G. boninense could provide the ideal long-term solution to basal stem rot. The total resistance of palms to G. boninense has not yet been reported, and few examples of partial resistances have been observed. Importantly, basidiospores are now recognized as the method by which the disease is spread, and control methods require to be revaluated because of this phenomenon. Many methods developed to prevent the spread of the disease effectively are only tested at nursery levels and are only reported in national journals inhibiting the development of useful techniques globally. The initial procedures employed by the fungus to infect the OP require consideration in terms of the physiology of the growth of the fungus and its possible control. This review assesses critically the progress that has been made in BSR development and management in OP.

Isolation and Selection of Streptomyces Species from Semi-arid Agricultural Soils and Their Potential as Producers of Xylanases and Cellulases

The Mezquital Valley (MV), Mexico, is a semi-arid region whose main economic activity is agriculture, this zone is characterized by the use of wastewater for crop irrigation. This condition has increased the amount nutrients in soils, organic carbon content and native microorganisms. The Streptomyces species are a group of saprophytic bacteria that represent between 20 and 60% of the total microbial population in soils, capable of producing metabolites of commercial importance. In this work, Streptomyces species were isolated from agricultural soils of the MV and was evaluated the production of endoglucanases (CMCase) and xylanases (Xyl) in Solid-State Cultivation (SSC). From soil samples, 73 possible strains of Streptomyces species were isolated for their ability to produce CMCase and Xyl in SSC. The study also included its characterization by morphological characteristics. Of the isolated microorganisms, 38 strains were selected as strong enzyme producers according to the measurement of the halo generated in plate and by growth on barley straw as only carbon source. Two different sizes of barley straw particle were tested, finding that the greatest enzymatic activity was observed in particle size 12. Three strains of Streptomyces species were chosen which presented the best catalytic capacities, a maximum of 100.69 AU Xyl/gram dry matter (gdm), 82 AU Xyl/gdm and 26.02 AU CMCase/gdm for strains 30, 28 and 12, respectively. The strains were identified by ribosomal gen16s sequence and identified as S. flavogriseus, S. virginiae and S. griseoaurantiacus. It is the first report of endogluconase and xylanolytic activity by S. virginiae isolated from a semi-arid soil.

Investigation of the influence of biofertilizer synthesized using microbial inoculums on the growth performance of two agricultural crops

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Biofertilizer was produced by aerobic composting method.

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Actinomycetes isolated was found to be good agents for biofertilizer synthesis.

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Organic matter and Carbon content of the composts was found to be decreasing.

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Nitrogen contents increased significantly with time.

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Leaf area index revealed 10th week as the optimum growth period for Maize and Okra.

In this work, biofertilizer was synthesized by mixing sawdust and other nitrogenous agricultural wastes into composites in the following ways: S1 (sawdust + chicken litter + vegetable waste), S2 (sawdust + sewage sludge + vegetable waste) and S3 (sawdust only as the control) respectively using actinomycetes as the microbial inoculums. In-vessel method of composting was employed with 120 L capacity polyethylene (PET) container as the bioreactor for the pilot scale study. Microorganisms were isolated from landfill extracts. Aeration was accomplished through turning of the compost twice weekly. Nitrogen, Carbon, Organic Matter and pH were determined at 5days intervals till the end of composting exercise. Flame Atomic Absorption Spectrometer (FAAS), was used for determination of the mineral composition of the raw materials and end products. American Society for Testing and Materials was used in the Analysis of Nitrogen, Carbon, and Organic Matter contents. Biofertilizer was analyzed more for activeness as organic fertilizer in the field studies using two crops (Maize and Okra). Biochemical test revealed that six genera of Actinomycetes were isolated. Inorganic salt starch agar medium was noticed to be effective isolation media for Actinomycetes. Actinomycetes were found to be good agents for biofertilizer synthesis due to their ability to mineralize nitrogen during composting. Preliminary investigation revealed that Rothia spp gave the highest percentage degradation of cellulose (21.6 %) as well as highest percentage mineralization of nitrogen (6.87 %) after 21days of incubation. Dosage ratio of 2:1:1 w: w, moisture content of 50–60 % and 25 days was found to be the optimum condition for nitrogen mineralization. Organic matter content of composts S1 and S2 decreased significantly with time while total kjeldahl nitrogen (TkN) content of the composts increased except compost S3 which on the contrary, reduced. The maximum temperature achieved at the end of 25 days compositing of substrate S2 was 64.6 ℃. Analysis of the leaf area index (LAI) revealed 10th week after transplant to be the period of optimum growth for both crops. In addition to, all the analysis conducted pointed to the fact that influence of biofertilizer on Okra and Maize growth performance is equivalent to the growth performance of chemical fertilizer on the same crops, affirming that organic fertilizer can comfortably replace chemical fertilizer in future.

New Antimicrobial Phenyl Alkenoic Acids Isolated from an Oil Palm Rhizosphere-Associated Actinomycete, Streptomyces palmae CMU-AB204T

Basal stem rot (BSR), or Ganoderma rot disease, is the most serious disease associated with the oil palm plant of Southeast Asian countries. A basidiomycetous fungus, Ganoderma boninense, is the causative microbe of this disease. To control BSR in oil palm plantations, biological control agents are gaining attention as a major alternative to chemical fungicides. In the course of searching for effective actinomycetes as potential biological control agents for BSR, Streptomyces palmae CMU-AB204^T was isolated from oil palm rhizosphere soil collected on the campus of Chiang Mai University. The culture broth of this strain showed significant antimicrobial activities against several bacteria and phytopathogenic fungi including G. boninense. Antifungal and antibacterial compounds were isolated by antimicrobial activity-guided purification using chromatographic methods. Their structures were elucidated by spectroscopic techniques, including Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), Ultraviolet (UV), and Infrared (IR) analyses. The current study isolated new phenyl alkenoic acids 1-6 and three known compounds, anguinomycin A (7), leptomycin A (8), and actinopyrone A (9) as antimicrobial agents. Compounds 1 and 2 displayed broad antifungal activity, though they did not show antibacterial activity. Compounds 3 and 4 revealed a strong antibacterial activity against both Gram-positive and Gram-negative bacteria including the phytopathogenic strain Xanthomonas campestris pv. oryzae. Compounds 7-9 displayed antifungal activity against Ganoderma. Thus, the antifungal compounds obtained in this study may play a role in protecting oil palm plants from Ganoderma infection with the strain S. palmae CMU-AB204^T.

Diversity and Applications of Endophytic Actinobacteria of Plants in Special and Other Ecological Niches

Actinobacteria are wide spread in nature and represent the largest taxonomic group within the domain Bacteria. They are abundant in soil and have been extensively explored for their therapeutic applications. This versatile group of bacteria has adapted to diverse ecological habitats, which has drawn considerable attention of the scientific community in recent times as it has opened up new possibilities for novel metabolites that may help in solving some of the most challenging problems of the day, for example, novel drugs for drug-resistant human pathogens, affordable means to maintain ecological balance in various habitats, and alternative practices for sustainable agriculture. Traditionally, free dwelling soil actinobacteria have been the subject of intensive research. Of late, symbiotic actinobacteria residing as endophytes within the plant tissues have generated immense interest as potential source of novel compounds, which may find applications in medicine, agriculture, and environment. In the light of these possibilities, this review focuses on the diversity of endophytic actinobacteria isolated from the plants of extreme habitats and specific ecological niches. Furthermore, an attempt has been made to assign chemical class to the compounds obtained from endophytic actinobacteria. Potential therapeutic applications of these compounds and the utility of endophytic actinobacteria in agriculture and environment are discussed.

Compost supplementation with nutrients and microorganisms in composting process

The composting is an aerobic, microorganism-mediated, solid-state fermentation process by which different organic materials are transformed into more stable compounds. The product obtained is the compost, which contributes to the improvement of physical, chemical and microbiological properties of the soil. However, the compost usage in agriculture is constrained because of its long-time action and reduced supply of nutrients to the crops. To enhance the content of nutrients assimilable by the plants in the compost, its supplementation with nutrients and inoculation with microorganisms have been proposed. The objective of this work was to review the state of the art on compost supplementation with nutrients and the role played by the microorganisms involved (or added) in their transformation during the composting process. The phases of composting are briefly compiled and different strategies for supplementation are analyzed. The utilization of nitrogenous materials and addition of microorganisms fixing nitrogen from the atmosphere or oxidizing ammonia into more assimilable for plants nitrogenous forms are analyzed. Several strategies for nitrogen conservation during composting are presented as well. The supplementation with phosphorus and utilization of microorganisms solubilizing phosphorus and potassium are also discussed. Main groups of microorganisms relevant during the composting process are described as well as most important strategies to identify them. In general, the development of this type of nutrient-enriched bio-inputs requires research and development not only in the supplementation of compost itself, but also in the isolation and identification of microorganisms and genes allowing the degradation and conversion of nitrogenous substances and materials containing potassium and phosphorus present in the feedstocks undergoing the composting process. In this sense, most important research trends and strategies to increase nutrient content in the compost are provided in this work.

Endophytic actinobacteria: Diversity, secondary metabolism and mechanisms to unsilence biosynthetic gene clusters

Endophytic actinobacteria, which reside in the inner tissues of host plants, are gaining serious attention due to their capacity to produce a plethora of secondary metabolites (e.g. antibiotics) possessing a wide variety of biological activity with diverse functions. This review encompasses the recent reports on endophytic actinobacterial species diversity, in planta habitats and mechanisms underlying their mode of entry into plants. Besides, their metabolic potential, novel bioactive compounds they produce and mechanisms to unravel their hidden metabolic repertoire by activation of cryptic or silent biosynthetic gene clusters (BGCs) for eliciting novel secondary metabolite production are discussed. The study also reviews the classical conservative techniques (chemical/biological/physical elicitation, co-culturing) as well as modern microbiology tools (e.g. next generation sequencing) that are being gainfully employed to uncover the vast hidden scaffolds for novel secondary metabolites produced by these endophytes, which would subsequently herald a revolution in drug engineering. The potential role of these endophytes in the agro-environment as promising biological candidates for inhibition of phytopathogens and the way forward to thoroughly exploit this unique microbial community by inducing expression of cryptic BGCs for encoding unseen products with novel therapeutic properties are also discussed.