SECONDARY METABOLITES WITH ANTIBIOTIC ACTIVITY OF MARINE ACTINOBACTERIA

Marine actinobacteria are active producers and an unused rich source of various biologically active secondary metabolites, such as antibiotics, antitumor, antiviral and antiinflammatory compounds, biopesticides, plant growth hormones, pigments, enzymes, enzyme inhibitors.In this review describes data from current literature sources for the period from 2017 to 2021 about various bioactive compounds that produce marine actinobacteria, their antibiotic activity and biotechnological potential, the main groups of secondary metabolites and their producers.

Micropropagation of Cassava (Manihot esculenta Crantz): Review

Cassava is a vital crop to the food security of millions of people worldwide, particularly in Sub-Saharan Africa. Because the crop produced a reasonable yield on marginal soils, it could help relieve global hunger. As a result, increasing cassava output and its quality attributes are significant. However, the low multiplication rate of this main crop has resulted in the delayed dissemination of improved varieties among farmers. As a result, tissue culture techniques may be a feasible solution for overcoming these challenges. Cassava in vitro propagation had done using either the shoots multiplication technique or somatic embryogenesis. However, the shoot multiplication approach is preferable since it retains clonal fidelity. Plant regeneration via somatic embryogenesis or organogenesis entailed the use of numerous basal media containing various plant growth hormones. Several studies found that each type of cassava clone required a unique protocol to achieve optimal shoot initiation, shoot multiplication, root induction, and elongation. This review describes recent research on cassava micropropagation that makes use of a variety of experimental systems. While each of these systems focuses on a different aspect of technique, they can be significant in understanding the in vitro production of cassava planting material.

Metagenomic insights into plant growth promoting genes inherent in bacterial endophytes of Emilia sonchifolia (Linn.) DC

Studies on the genome of endophytes reveal the metabolic potential of endophytic microbiome including both culturable and unculturable fractions. The metagenome analysis through the Illumina HiSeq platform gives access to the genetic data encrypted for the molecular machinery, which takes part in plant growth promotion activity of the endophyte in various aspects including production of plant growth hormones and enhancing nutrient availability for the host plant. The present work was undertaken to identify the genes involved in plant growth promotion activities from the endophytes of Emilia sonchifolia(Linn.) DC. through metagenome analysis. Metagenomic studies include the analysis of functional annotations which aid in the detection of biocatalysts taking part in the metabolic pathway of host plants. The annotations of expressed genes in different databases like NCBI Nr, KEGG, eggnog and CAZy resulted in enlisting the vast array of information on the genetic diversity of the endophytic microbiome. The metagenome analysis of endophytic bacteria from the medicinal plant E.sonchifolia unveiled characteristic functional genes involved in plant growth promotion such as nitrogen metabolism (nif) and siderophore production (enterobactin category), ipdC and tnaA (IAA producing), ACC deaminase coding genes (regulation of elevated ethylene levels in host tissues), Mo-Nitrogenase, nitrous-oxide reductase (nosZ), nitrate reductase (narG, napA), nitrite reductase (nirD) (nutrient assimilation and absorption) enterobactin siderophore synthetase components F and D and acid phosphatase genes. This clearly explains the effective plant-microbe relationship and the role of bacterial endophytic microbes in regulating the growth of host plants.

Effect of Vacuum Impregnation with Sucrose and Plant Growth Hormones to Mitigate the Chilling Injury in Spinach Leaves

Vacuum impregnation (VI) has been immensely used in modifying the physicochemical properties, nutritional values and sensory attributes of fruits and vegetables. However, the metabolic consequences of the plant tissue upon impregnation have not been profoundly explored although shelf life is strongly dependent on this factor. In this study, spinach leaves were impregnated with salicylic acid (SA), γ-aminobutyric acid (GABA) and sucrose to improve its quality and storage ability by reducing the chilling injury through the improvement of proline content. The spinach leaves were stored at 4 °C for 7 days and were analyzed at 12 h interval. Upon 1 day of impregnation, the proline content in GABA, sucrose and SA impregnated leaves was increased by 240%, 153% and 103%, respectively, while in non-impregnated leaves, the proline content was decreased by 23.8%. The chlorophyll content of GABA impregnated leaves exhibited the lowest reduction (49%) followed by sucrose (55%) and SA (57%); meanwhile, non-impregnated leaves reduced 80% of chlorophyll content at the end of storage. Sensory evaluation showed that GABA, sucrose and SA impregnated leaves respectively, obtained higher score in terms of freshness, color, texture and overall appearance as compared to non-impregnated leaves.

Potentiality of Vermicomposting in the South Pacific Island Countries: A Review

Incorporation of vermin culture in the composting system produces “vermicompost”, an enriched biofertilizer known to improve the physical, chemical, and biological properties of soil. It is applied in granular form and/or in liquid solution (vermiwash), and in both open fields and greenhouses. Vermicompost has been shown to contain plant growth hormones, which stimulate seed germination and improve crop yield, the ‘marketability’ of products, plant physiology, and their ability to fight against disease. In recent years, South Pacific island countries (SPICs) have placed an increasing emphasis on the importance of organic agricultural practices as a means of achieving more sustainable and environmentally friendly farming practices. However, vermiculture is not practiced in South Pacific island countries (SPICs) largely due to the lack of awareness of this type of application. We consider the inclusion of vermiculture in this region as a potential means of achieving sustainable organic agricultural practices. This study represents a systematic review in which we collect relevant information on vermicomposting and analyze the applicability of this practice in the SPICs based on these nations’ physical, socioeconomic, and climatic conditions. The tropical climate of the SPICs means that they meet the combined requirements of a large available biomass for composting and the availability of earthworms. Perionyx excavatus and Pontoscolex corethrurus have been identified as potential native earthworm species for vermicomposting under the conditions of the SPICs. Eisenia fetida, a well-known earthworm species, is also effectively adapted to this region and reported to be an efficient species for commercial vermicomposting. However, as a new input into the local production system, there may be unforeseen barriers in the initial stages, as with other advanced technologies, and the introduction of vermiculture as a practice requires a steady effort and adaptive research to achieve success. Further experimental research is required to analyze the productivity and profitability of using the identified native earthworm species for vermiculture using locally available biomass in the SPICs.

Effect of Foliar Application of Plant Growth Hormones on Yield and Quality Parameters in Ajowan (Trachyspermum ammi L. Sprague)

Foliar application of plant growth regulators viz., GA3 -50& 100 ppm, NAA- 50 ppm &100 ppm, Thiourea- 250 & 500 ppm, 28-Homobrassinolide- 0.1& 0.2ppm, Triacontanol - 2.5& 5 ppm and Control. All the treatments were applied as foliar sprays at 30 and 45 DAT. Days to 50% flowering (46 d) and days to harvest (100.20 d) were found earlier in ajowan with the foliar applications of triacontanol by 5 ppm (T10).The same treatment had recorded the maximum number of umbellate umbel-1(14.20). Foliar applications of thiourea by 250 ppm (T5) had record the highest values with respect to yield, yield attributing characters viz number of umbels plant-1(228.70), number of seeds umbel-1(183.60), number of seeds umbellate-1(13.50), test weight (1.56 g), seed yield plant-1 (28.50 g), seed yield plot-1 (1425 g), seed yield hectare-1(1583.33 kg), harvest index (69.71%) and quality parameters viz essential oil (3.64%) and protein contents (19.26 mg 100 g-1).

Role of Microbial Enriched Vermicompost in Plant-Parasitic Nematode Management

Earthworm causes increase in availability of soil organic matter through degradation of dead matters by microbes, leaf litter and porocity of soil. Vermicompost is a non-thermophilic biodegradation process of waste organic material through the action of microorganism with earthworm. Vermicompost is rich in many nutrients including calcium, nitrates, phosphorus and soluble potassium, which are essentially required for plant growth. Different plant growth hormones like gibberellins, auxins and cytokinins are present in vermicompost, which has microbial origin. Nematodes are mostly small, colorless and microscopic organisms which remain under soil, fresh or marine water, plants or animals, and act as parasite in different conditions, while very few have direct effect on human. The nematodes which are parasitic on plants use plant tissues as their food. They have well developed spearing device, like a hypodermic needle called stylet. It is used to penetrate host cell membrane. Management of plant-parasitic-nematodes therefore is necessary and several means are adopted. Of which, use of bio-chemicals and organic compost have shown encouraging results and proved to be potential in suppressing the nematode population. Vermicompost plays an important role of soil fortification on growth characteristics, such as length, weight, root, shoot branches, number of leaves and metabolism of host plant against nematode infection. Vermicompost fortified plants showed increment in sugar, protein and lipid over untreated control. Increment of these metabolites helps treated plants to metabolically cope up the infection and promotes excessive plant growth. The vermicompost caused the mortality of nematodes by the release of nematicidal substances such as hydrogen sulfate, ammonia, and nitrite apart from promotion of the growth of nematode predatory fungi that attack their cysts. It favours rhizobacteria which produce toxic enzymes and toxins; or indirectly favors population of nematophagous microorganisms, bacteria, and fungi, which serve as food for predatory or omnivorous nematodes, or arthropods such as mites, which are selectively opposed to plant-parasitic nematodes.

Comparative Study between Exogenously Applied Plant Growth Hormones versus Metabolites of Microbial Endophytes as Plant Growth-Promoting for Phaseolus vulgaris L.

Microbial endophytes organize symbiotic relationships with the host plant, and their excretions contain diverse plant beneficial matter such as phytohormones and bioactive compounds. In the present investigation, six bacterial and four fungal strains were isolated from the common bean (Phaseolus vulgaris L.) root plant, identified using molecular techniques, and their growth-promoting properties were reviewed. All microbial isolates showed varying activities to produce indole-3-acetic acid (IAA) and different hydrolytic enzymes such as amylase, cellulase, protease, pectinase, and xylanase. Six bacterial endophytic isolates displayed phosphate-solubilizing capacity and ammonia production. We conducted a field experiment to evaluate the promotion activity of the metabolites of the most potent endophytic bacterial (Bacillus thuringiensis PB2 and Brevibacillus agri PB5) and fungal (Alternaria sorghi PF2 and, Penicillium commune PF3) strains in comparison to two exogenously applied hormone, IAA, and benzyl adenine (BA), on the growth and biochemical characteristics of the P. vulgaris L. Interestingly, our investigations showed that bacterial and fungal endophytic metabolites surpassed the exogenously applied hormones in increasing the plant biomass, photosynthetic pigments, carbohydrate and protein contents, antioxidant enzyme activity, endogenous hormones and yield traits. Our findings illustrate that the endophyte Brevibacillus agri (PB5) provides high potential as a stimulator for the growth and productivity of common bean plants.

Rhizosphere Engineering With Plant Growth-Promoting Microorganisms for Agriculture and Ecological Sustainability

The rhizosphere is undoubtedly the most complex microhabitat, comprised of an integrated network of plant roots, soil, and a diverse consortium of bacteria, fungi, eukaryotes, and archaea. The rhizosphere conditions have a direct impact on crop growth and yield. Nutrient-rich rhizosphere environments stimulate plant growth and yield and vice versa. Extensive cultivation exhaust most of the soils which need to be nurtured before or during the next crop. Chemical fertilizers are the major source of crop nutrients but their uncontrolled and widespread usage has posed a serious threat to the sustainability of agriculture and stability of an ecosystem. These chemicals are accumulated in the soil, drained in water, and emitted to the air where they persist for decades causing a serious threat to the overall ecosystem. Plant growth-promoting rhizobacteria (PGPR) present in the rhizosphere convert many plant-unavailable essential nutrients e.g., nitrogen, phosphorous, zinc, etc. into available forms. PGPR produces certain plant growth hormones (such as auxin, cytokinin, and gibberellin), cell lytic enzymes (chitinase, protease, hydrolases, etc.), secondary metabolites, and antibiotics, and stress alleviating compounds (e.g., 1-Aminocyclopropane-1- carboxylate deaminase), chelating agents (siderophores), and some signaling compounds (e.g., N-Acyl homoserine lactones) to interact with the beneficial or pathogenic counterparts in the rhizosphere. These multifarious activities of PGPR improve the soil structure, health, fertility, and functioning which directly or indirectly support plant growth under normal and stressed environments. Rhizosphere engineering with these PGPR has a wide-ranging application not only for crop fertilization but developing eco-friendly sustainable agriculture. Due to severe climate change effects on plants and rhizosphere biology, there is growing interest in stress-resilient PGPM and their subsequent application to induce stress (drought, salinity, and heat) tolerance mechanism in plants. This review describes the three components of rhizosphere engineering with an explicit focus on the broader perspective of PGPM that could facilitate rhizosphere engineering in selected hosts to serve as an efficient component for sustainable agriculture.

Molecular interplay between phytohormones and geminiviruses: a saga of a never-ending arms race

Geminiviruses can infect a wide range of plant hosts worldwide and have hence become an emerging global agroeconomic threat. The association of these viruses with satellite molecules and highly efficient insect vectors such as whiteflies further prime their devastating impacts. Plants elicit a strong antiviral immune response to restrict the invasion of these destructive pathogens. Phytohormones help plants to mount this response and occupy a key position in combating these biotrophs. These defense hormones not only inhibit geminiviral propagation but also hamper viral transmission by compromising the performance of their insect vectors. Nonetheless, geminiviruses have co-evolved to have a few multitasking virulence factors that readily remodel host cellular machineries to circumvent the phytohormone-mediated manifestation of the immune response. Furthermore, these obligate parasites exploit plant growth hormones to produce a cellular environment permissive for virus replication. In this review, we outline the current understanding of the roles and regulation of phytohormones in geminiviral pathogenesis.