Bacterial Secondary Metabolites Research Articles

Exploring the roles of ribosomal peptides in prokaryote-phage interactions through deep learning-enabled metagenome mining

BackgroundMicrobial secondary metabolites play a crucial role in the intricate interactions within the natural environment. Among these metabolites, ribosomally synthesized and post-translationally modified peptides (RiPPs) are becoming a promising source of therapeutic agents due to their structural diversity and functional versatility. However, their biosynthetic capacity and ecological functions remain largely underexplored.ResultsHere, we aim to explore the biosynthetic profile of RiPPs and their potential roles in the interactions between microbes and viruses in the ocean, which encompasses a vast diversity of unique biomes that are rich in interactions and remains chemically underexplored. We first developed TrRiPP to identify RiPPs from ocean metagenomes, a deep learning method that detects RiPP precursors in a hallmark gene-independent manner to overcome the limitations of classic methods in processing highly fragmented metagenomic data. Applying this method to metagenomes from the global ocean microbiome, we uncover a diverse array of previously uncharacterized putative RiPP families with great novelty and diversity. Through correlation analysis based on metatranscriptomic data, we observed a high prevalence of antiphage defense-related and phage-related protein families that were co-expressed with RiPP families. Based on this putative association between RiPPs and phage infection, we constructed an Ocean Virus Database (OVD) and established a RiPP-involving host-phage interaction network through host prediction and co-expression analysis, revealing complex connectivities linking RiPP-encoding prokaryotes, RiPP families, viral protein families, and phages. These findings highlight the potential of RiPP families involved in prokaryote-phage interactions and coevolution, providing insights into their ecological functions in the ocean microbiome.ConclusionsThis study provides a systematic investigation of the biosynthetic potential of RiPPs from the ocean microbiome at a global scale, shedding light on the essential insights into the ecological functions of RiPPs in prokaryote-phage interactions through the integration of deep learning approaches, metatranscriptomic data, and host-phage connectivity. This study serves as a valuable example of exploring the ecological functions of bacterial secondary metabolites, particularly their associations with unexplored microbial interactions.CSrTVep6AzTb_yem78LPYEVideo

A taste of a toxin paradise: Xenorhabdus and Photorhabdus bacterial secondary metabolites against Aedes aegypti larvae and eggs

Aedes-transmitted arboviral infections such as Dengue, Yellow Fever, Zika and Chikungunya are increasing public health problems. Xenorhabdus and Photorhabdus bacteria are promising sources of effective compounds with important biological activities. This study investigated the effects of cell-free supernatants of X. szentirmaii, X. cabanillasii and P. kayaii against Ae. aegypti eggs and larvae and identified the bioactive larvicidal compound in X. szentirmaii using the easyPACId approach. Among the three tested bacterial species, X. cabanillasii exhibited the highest (96%) egg hatching inhibition and larvicidal activity (100% mortality), whereas P. kayaii was the least effective species in our study. EasyPACId method revealed that bioactive larvicidal compound in the bacterial supernatant was fabclavine. Fabclavines obtained from promoter exchange mutants of different bacterial species such as X. cabanillasii, X. budapestensis, X. indica, X. szentirmaii, X. hominckii and X. stockiae were effective against mosquito larvae. Results show that these bacterial metabolites has a potential to be used in integrated pest management (IPM) programmes of mosquitoes.

Isolation and characterization of Chromobacterium violaceum and antibacterial activities of its metabolite violacein

Violacein is a naturally-occurring bacterial secondary metabolite which is known to demonstrate a wide range of biological properties including antibacterial, antifungal, antiviral as well as anticancer and antitumor activities. Bacteria belonging to the genus Chromobacterium are the most studied microorganisms for violacein production. In this study, indigenous violacein-producing Chromobacterium violaceum was isolated from water and sediment samples of Bijaypur white clay hill lake, Netrokona, Bangladesh, and identified by biochemical and molecular characterization. After confirming the presence of the vioB gene in a polymerase chain reaction, crude violacein was purified from C. violaceum CV1 by ethanol extraction followed by filtration through 0.22 µm syringe filters. The partially-purified pigment exhibited significant antibacterial activity against three Gram-positive pathogens; Staphylococcus aureus, Streptococcus sp, and Listeria monocytogenes, with the later demonstrating the highest sensitivity. The bactericidal activity was more pronounced when combined with an antibiotic, thereby producing a drug-metabolite synergistic antibacterial activity. Dhaka Univ. J. Biol. Sci. 33(1): 109-119, 2024 (January)

Diversity and distribution of biosynthetic gene clusters in agricultural soil microbiomes.

Bacterial secondary metabolites serve as an important source of molecules for drug discovery. They also play an important function in mediating the interactions of microbial producers with their living environment and surrounding organisms. However, little is known about the genetic novelty, distribution, and community-level impacts of soil bacterial biosynthetic potential on a large geographic scale. Here, we constructed the first catalog of 11,149 biosynthetic gene clusters (BGCs) from agricultural soils across China and unearthed hidden biosynthetic potential for new natural product discovery from the not-yet-cultivated soil bacteria. Notably, we revealed soil pH as the strongest environmental driver of BGC biogeography and predicted that soil acidification and global climate change could damage the biosynthetic potential of the soil microbiome. The co-occurrence network of bacterial genomes revealed two BGC-rich species, i.e., Nocardia niigatensis from Actinobacteriota and PSRF01 from Acidobacteriota, as the module hub and connector, respectively, indicating their keystone positions in the soil microbial communities. We also uncovered a dominant role of BGC-inferred biotic interactions over environmental drivers in structuring the soil microbiome. Overall, this study achieved novel insights into the BGC landscape in agricultural soils of China, substantially expanding our understanding of the diversity and novelty of bacterial secondary metabolism and the potential role of secondary metabolites in microbiota assembly.IMPORTANCEBacterial secondary metabolites not only serve as the foundation for numerous therapeutics (e.g., antibiotics and anticancer drugs), but they also play critical ecological roles in mediating microbial interactions (e.g., competition and communication). However, our knowledge of bacterial secondary metabolism is limited to only a small fraction of cultured strains, thus restricting our comprehensive understanding of their diversity, novelty, and potential ecological roles in soil ecosystems. Here, we used culture-independent metagenomics to explore biosynthetic potentials in agricultural soils of China. Our analyses revealed a high degree of genetic diversity and novelty within biosynthetic gene clusters in agricultural soil environments, offering valuable insights for biochemists seeking to synthesize novel bioactive products. Furthermore, we uncovered the pivotal role of BGC-rich species in microbial communities and the significant relationship between BGC richness and microbial phylogenetic turnover. This information emphasizes the importance of biosynthetic potential in the assembly of microbial communities.

The Influence of Lactobacillus spp. Secondary Metabolites Isolated from Immature Egyptian Honey on Human Pathogens, Transcription of Virulence Genes and Lung Cancer

The Influence of Lactobacillus spp. Secondary Metabolites Isolated from Immature Egyptian Honey on Human Pathogens, Transcription of Virulence Genes and Lung Cancer

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria.

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

Effects of Lactobacillus plantarum and Bacillus subtilis on growth, immunity and intestinal flora of largemouth bass(Micropterus salmoides)

Probiotics play a crucial role in largemouth bass aquaculture, primarily in enhancing water quality, preventing fish diseases, promoting largemouth bass growth, and boosting immunity in high-density culture conditions. The experiment was actualized by adding Lactobacillus plantarum, Bacillus subtilis and a mixture of probiotic (L. plantarum and B. subtilis 1:1) in the culture water of largemouth bass for 42 days, respectively, to explore the effect of the above two probiotics on the growth performance and immunity ability of largemouth bass (Micropterus salmoides).Results: At the level of phylum, the relative abundance of enteric flora in Tenericutes of largemouth bass in L. plantarum added group was significantly higher than that in control group (p < 0.05). Conversely, the relative abundance of Proteobacteria was significantly lower than that of control group (p < 0.05). Similarly, at the genus level, the relative abundance of Mycoplasma and Leifsonia was significantly higher than that of control group (p < 0.05), while the relative abundance of Aeromonas was significantly lower in the L. plantarum added group compared to the control group (p < 0.05). Compared with the control group, there were no significant differences in phylum level in the B. subtilis added group (p < 0.05), and the relative abundance of Plesiomonas was significantly increased (p < 0.05), the relative abundance of Aeromonas was significantly decreased at genus level (p < 0.05). The relative abundance of Plesiomonas and Parabacteroides in the mixed probiotic treatment group was significantly increased (p < 0.05), the relative abundance of Aeromonas was significantly decreased at the level of genus (p < 0.05). The metabolites of carboxylic acid and its derivatives, organic oxygen compound, glycerophospholipid, lip acyl and other categories in enteric tissues of all treatment groups had significant changes (p < 0.05), enteric bacterial secondary metabolites such as SCFAs and 1-Phosphatidyl-D-myo-inositol were significantly increased (p < 0.05). The results showed that the addition of L. plantarum and B. subtilis in water could promote the growth of largemouth bass and increase its nonspecific immunity by enhancing the stability of enteric flora, increasing efficiency of enteric digestion and absorption and promoting the anti-inflammatory and immune ability of the body through secondary metabolites of enteric microbe.

Streptomyces Strains and Their Metabolites for Biocontrol of Phytopathogens in Agriculture.

Sustainable agriculture is increasingly linked to biological pesticides as alternatives to agro-chemicals. Streptomyces species suppress plant diseases through their unique traits and numerous metabolites. Although many Streptomyces strains have been developed into commercial products, their roles in the biocontrol of phytopathogens and mechanisms of functional metabolite synthesis remain poorly understood. In this review, biocontrol of plant diseases by Streptomyces is summarized on the basis of classification of fungal and bacterial diseases and secondary metabolites produced by Streptomyces that act on phytopathogenic microorganisms are discussed. The associated non-ribosomal peptide synthetases and polyketide synthetases responsible for biosynthesis of these secondary metabolites are also investigated, and advances in fermentation of Streptomyces are described. Finally, the need to develop precise and effective biocontrol methods for plant diseases is highlighted.

Prediction of Structure Activity Relationship (SAR) of Lactobacillus plantarum DA2 content for Cholesterol Reduction Treatment

Cholesterol is a chemical that is naturally created by the liver but can also be present in animal-based meals like meat and milk. Cholesterol is required by the body for the formation of healthy cells, the production of several hormones, and the production of vitamin D. Although cholesterol is necessary for the body, high levels can be harmful to one's health, hence therapy to lower cholesterol levels using natural products or the aid of bacterial metabolism is required. Lactobacillus plantarum 2DA is a lactic acid bacterium that has potential as a probiotic, so further analysis is needed on its ability as a therapy to reduce cholesterol through a bioinformatics approach. The method used in this research is to search for bacterial secondary metabolites by studying literature from published journals. Each compound is then searched in the PubChem database for its canonical structure and isomeric SMILE (simplified molecular-input line-entry system) and secondary metabolites in bacteria from the literature study were analyzed for potential using WAY2DRUG PASS prediction (http://www.pharmaexpert. ru/passonline/predict.php) as a cholesterol-lowering treatment. The results of the study based on the prediction of the SAR Way2 Drug Pass Server seen in the Probability To Be Active (Pa) values obtained 0.45, 0.49 and 0.37 for anti-hypercholesterolemic, cholesterol antagonist and cholesterol oxidase inhibitors. From the results obtained, it can be recommended that Lactobacillus plantarum 2DA can be further researched in vivo for cholesterol-lowering therapy.

Structure Prediction and Genome Mining-Aided Discovery of the Bacterial C-Terminal Tryptophan Prenyltransferase PalQ.

Post-translational prenylations, found in eukaryotic primary metabolites and bacterial secondary metabolites, play crucial roles in biomolecular interactions. Employing genome mining methods combined with AlphaFold2-based predictions of protein interactions, PalQ , a prenyltransferase responsible for the tryptophan prenylation of RiPPs produced by Paenibacillus alvei, is identified. PalQ differs from cyanobactin prenyltransferases because of its evolutionary relationship to isoprene synthases, which enables PalQ to transfer extended prenyl chains to the indole C3position. This prenylation introduces structural diversity to the tryptophan side chain and also leads to conformational dynamics in the peptide backbone, attributed to the cis/trans isomerization that arises from the formation of a pyrrolidine ring. Additionally, PalQ exhibited pronounced positional selectivity for the C-terminal tryptophan. Such enzymatic characteristics offer a toolkit for peptide therapeutic lipidation.

Establishment of a transparent soil system to study Bacillus subtilis chemical ecology

Bacterial secondary metabolites are structurally diverse molecules that drive microbial interaction by altering growth, cell differentiation, and signaling. Bacillus subtilis, a Gram-positive soil-dwelling bacterium, produces a wealth of secondary metabolites, among them, lipopeptides have been vastly studied by their antimicrobial, antitumor, and surfactant activities. However, the natural functions of secondary metabolites in the lifestyles of the producing organism remain less explored under natural conditions, i.e. in soil. Here, we describe a hydrogel-based transparent soil system to investigate B. subtilis chemical ecology under controllable soil-like conditions. The transparent soil matrix allows the growth of B. subtilis and other isolates gnotobiotically and under nutrient-controlled conditions. Additionally, we show that transparent soil allows the detection of lipopeptides production and dynamics by HPLC-MS, and MALDI-MS imaging, along with fluorescence imaging of 3-dimensional bacterial assemblages. We anticipate that this affordable and highly controllable system will promote bacterial chemical ecology research and help to elucidate microbial interactions driven by secondary metabolites.

Characterization of Pseudomonas capsici strains from pepper and tomato.

Disease outbreaks of bacterial leaf spot and blight of pepper and tomato often occur in both transplant- and field-production systems worldwide. In some cases, the outbreaks are caused by novel bacterial species. Characterization of these novel bacterial species are critical in developing diagnostic assays and identifying management options for pathogen monitoring and sustainable production, respectively. We characterized strains belonging to novel Pseudomonas species that are responsible for outbreaks in pepper and tomato both in transplant-houses and in production fields in Georgia, USA. Phylogenomic analyses and whole genome sequence indices demonstrated that the pepper and tomato strains belonged to P. capsici. The whole-genome comparison revealed that 13 Pseudomonas strains from diverse isolation sources that were curated in NCBI were indeed P. capsici indicating a potential wide-host range for this bacterial species. Our greenhouse-based host-range assay also indicated that P. capsici strains were pathogenic on pepper, tomato, eggplant, cabbage, lettuce, and watermelon corroborating a wide-host-range. A phylogenetic tree inferred from the whole genome sequence data showed that the P. capsici strains from Georgia (pepper and tomato) were genetically diverse, and were closely related to tomato P. capsici strains from Florida. Genomic presence of traditional bacterial virulence factors in P. capsici strains was also determined. Pseudomonascapsici strains encode one set of type I secretion system, two sets of type II secretion systems, one set of type III secretion system, two sets of type V secretion systems, three sets of type VI secretion systems, and various secondary metabolite gene clusters including lipopeptides. In in-vitro assays, it was demonstrated that six out of seven P. capsici strains (pepper and tomato strains from Georgia) were not sensitive to 0.8 mM CuSO4. When the genomes of copper-tolerant strains were compared with the copper-sensitive strains, it was observed that the former strains encode a cluster of genes related to copper tolerance, which were absent in the genomes of copper-sensitive strains. Considering the ability of P. capsici strains to infect a range of vegetable hosts and possession of a wide range of bacterial virulence factors, secondary metabolites, and copper-tolerance genes, we envision that the management of this pathogen might potentially be a challenge.

The Golgi stacking protein GRASP55 is targeted by the natural compound prodigiosin

BackgroundThe bacterial secondary metabolite prodigiosin has been shown to exert anticancer, antimalarial, antibacterial and immunomodulatory properties. With regard to cancer, it has been reported to affect cancer cells but not non-malignant cells, rendering prodigiosin a promising lead compound for anticancer drug discovery. However, a direct protein target has not yet been experimentally identified.MethodsWe used mass spectrometry-based thermal proteome profiling in order to identify target proteins of prodigiosin. For target validation, we employed a genetic knockout approach and electron microscopy.ResultsWe identified the Golgi stacking protein GRASP55 as target protein of prodigiosin. We show that prodigiosin treatment severely affects Golgi morphology and functionality, and that prodigiosin-dependent cytotoxicity is partially reduced in GRASP55 knockout cells. We also found that prodigiosin treatment results in decreased cathepsin activity and overall blocks autophagic flux, whereas co-localization of the autophagosomal marker LC3 and the lysosomal marker LAMP1 is clearly promoted. Finally, we observed that autophagosomes accumulate at GRASP55-positive structures, pointing towards an involvement of an altered Golgi function in the autophagy-inhibitory effect of this natural compound.ConclusionTaken together, we propose that prodigiosin affects autophagy and Golgi apparatus integrity in an interlinked mode of action involving the regulation of organelle alkalization and the Golgi stacking protein GRASP55.8brCwiZ4E3PVMoFvaLMguTVideo

Identification of the bacterial metabolite aerugine as potential trigger of human dopaminergic neurodegeneration

The causes of nigrostriatal cell death in idiopathic Parkinson’s disease are unknown, but exposure to toxic chemicals may play some role. We followed up here on suggestions that bacterial secondary metabolites might be selectively cytotoxic to dopaminergic neurons. Extracts from Streptomyces venezuelae were found to kill human dopaminergic neurons (LUHMES cells). Utilizing this model system as a bioassay, we identified a bacterial metabolite known as aerugine (C10H11NO2S; 2-[4-(hydroxymethyl)-4,5-dihydro-1,3-thiazol-2-yl]phenol) and confirmed this finding by chemical re-synthesis. This 2-hydroxyphenyl-thiazoline compound was previously shown to be a product of a wide-spread biosynthetic cluster also found in the human microbiome and in several pathogens. Aerugine triggered half-maximal dopaminergic neurotoxicity at 3–4 µM. It was less toxic for other neurons (10–20 µM), and non-toxic (at <100 µM) for common human cell lines. Neurotoxicity was completely prevented by several iron chelators, by distinct anti-oxidants and by a caspase inhibitor. In the Caenorhabditis elegans model organism, general survival was not affected by aerugine concentrations up to 100 µM. When transgenic worms, expressing green fluorescent protein only in their dopamine neurons, were exposed to aerugine, specific neurodegeneration was observed. The toxicant also exerted functional dopaminergic toxicity in nematodes as determined by the “basal slowing response” assay. Thus, our research has unveiled a bacterial metabolite with a remarkably selective toxicity toward human dopaminergic neurons in vitro and for the dopaminergic nervous system of Caenorhabditis elegans in vivo. These findings suggest that microbe-derived environmental chemicals should be further investigated for their role in the pathogenesis of Parkinson's disease.

Genomic and clinical characterization of Klebsiella pneumoniae carrying the pks island.

The pks island and its production of the bacterial secondary metabolite genotoxin, colibactin, have attracted increasing attention. However, genomic articles focusing on pks islands in Klebsiella pneumoniae, as well as comparative genomic studies of mobile genetic elements, such as prophages, plasmids, and insertion sequences, are lacking. In this study, a large-scale analysis was conducted to understand the prevalence and evolution of pks islands, differences in mobile genetic elements between pks-negative and pks-positive K. pneumoniae, and clinical characteristics of infection caused by pks-positive K. pneumoniae. The genomes of 2,709 K. pneumoniae were downloaded from public databases, among which, 1,422 were from NCBI and 1,287 were from the China National GeneBank DataBase (CNGBdb). Screening for virulence and resistance genes, phylogenetic tree construction, and pan-genome analysis were performed. Differences in mobile genetic elements between pks-positive and pks-negative strains were compared. The clinical characteristics of 157 pks-positive and 157 pks-negative K. pneumoniae infected patients were investigated. Of 2,709 K. pneumoniae genomes, 245 pks-positive genomes were screened. The four siderophores, type VI secretion system, and nutritional factor genes were present in at least 77.9% (191/245), 66.9% (164/245), and 63.3% (155/245) of pks-positive strains, respectively. The number and fragment length of prophage were lower in pks-positive strains than in pks-negative strains (p < 0.05). The prevalence of the IS6 family was higher in pks-negative strains than in pks-positive strains, and the prevalence of multiple plasmid replicon types differed between the pks-positive and pks-negative strains (p < 0.05). The detection rate of pks-positive K. pneumoniae in abscess samples was higher than that of pks-negative K. pneumoniae (p < 0.05). The pks-positive strains had abundant virulence genes. There were differences in the distribution of mobile genetic elements between pks-positive and pks-negative isolates. Further analysis of the evolutionary pattern of pks island and epidemiological surveillance in different populations are needed.

Antimicrobial Bacterial Metabolites: Properties, Applications and Loading in Liposomes for Site-specific Delivery.

The high levels of antibiotic resistance registered worldwide have become a serious health problem, threatening the currently available treatments for a series of infectious diseases. With antibiotics becoming less and less effective, it is becoming increasingly difficult and, in some cases, impossible to treat patients with even common infectious diseases, such as pneumonia. The inability to meet the ever-increasing demand to control microbial infection requires both the search for new antimicrobials and improved site-specific delivery. On the one hand, bacterial secondary metabolites are known for their diverse structure and antimicrobial potential and have been in use for a very long time in diverse sectors. A good deal of research is produced annually describing new molecules of bacterial origin with antimicrobial properties and varied applications. However, very few of these new molecules reach the clinical phase and even fewer are launched in the market for use. In this review article, we bring together information on these molecules with potential for application, in particular, for human and veterinary medicine, and the potential added value of the use of liposomes as delivery systems for site-specific delivery of these drugs with the synergistic effect to overcome the risk of antibiotic resistance.

Citrate Synthase GltA Modulates the 2,4-Diacetylphloroglucinol Biosynthesis of Pseudomonas fluorescens 2P24 and is Essential for the Biocontrol Capacity.

Carbon metabolism is critical for microbial physiology and remarkably affects the outcome of secondary metabolite production. The production of 2,4-diacetylphloroglucinol (2,4-DAPG), a bacterial secondary metabolite with a broad spectrum of antibiotic activity, is a major mechanism used by the soil bacterium Pseudomonas fluorescens 2P24 to inhibit the growth of plant pathogens and control disease occurrence. Strain 2P24 has evolved a complex signaling cascade to regulate the production of 2,4-DAPG. However, the role of the central carbon metabolism in modulating 2,4-DAPG production has not been fully determined. In this study, we report that the gltA gene, which encodes citrate synthase, affects the expression of the 2,4-DAPG biosynthesis gene and is essential for the biocontrol capacity of strain 2P24. Our data showed that the mutation of gltA remarkably decreased the biosynthesis of 2,4-DAPG. Consistent with this result, the addition of citrate in strain 2P24 resulted in increased 2,4-DAPG production and decreased levels of RsmA and RsmE. In comparison with the wild-type strain, the gltA mutant was severely impaired in terms of biocontrol activity against the bacterial wilt disease of tomato plants caused by Ralstonia solanacearum. Moreover, the gltA mutant exhibited increased antioxidant activity, and the expression of oxidative, stress-associated genes, including ahpB, katB, and oxyR, was significantly upregulated in the gltA mutant compared to the wild-type strain. Overall, our data indicate that the citrate synthase GltA plays an important role in the production of 2,4-DAPG and oxidative stress and is required for biocontrol capacity.

Endophytic Streptomyces population induced by L-glutamic acid enhances plant resilience to abiotic stresses in tomato.

Endophyte bacteria, which colonize plants including roots, stem, flower, and fruit, it can derive their nutrients from the host, are recognized for their mutualistic relationship with the host plant. They play a critical role in promoting host growth and modulating abiotic stress. Carbon and nitrogen have a significant impact on bacterial population and secondary metabolite production, which are highly specific in various categories such as bacterial growth regulation, anti-compounds production. Application of L-glutamic acid can significantly enhance Streptomyces globisporus population buildup in plants. However, the effectiveness of this population buildup against abiotic stresses such as salinity and drought has not been investigated. Therefore, in this study, we tested the bacteria and their prebiotic activity against salinity and drought stress in tomato plants. Three different amino acids were treated on the tomato plants, and it was observed that L-asparagine and L-proline had a negative effect on plant growth and phenotype, while L-glutamic acid promoted plant growth and increased bacteria population density. The bacteria were found to colonize the rhizosphere and root endosphere, with colonization being promoted by L-glutamic acid. Additionally, Streptomyces was found to have plant growth promotion effects and provided protection against abiotic stresses. Interestingly, L-glutamic acid reduced the damage caused by salinity stress, but not drought stress. These findings suggest that L-glutamic acid plays a role in providing tolerance to salinity stress with the core microbiota, thus the current study demonstrated their prebiotic activity in the agriculture system.

GC Analysis, Anticancer, and Antibacterial Activities of Secondary Bioactive Compounds from Endosymbiotic Bacteria of Pomegranate Aphid and Its Predator and Protector.

Bacterial secondary metabolites are a valuable source of various molecules that have antibacterial and anticancer activity. In this study, ten endosymbiotic bacteria of aphids, aphid predators and ants were isolated. Bacterial strains were identified according to the 16S rRNA gene. Ethyl acetate fractions of methanol extract (EA-ME) were prepared from each isolated bacterium and tested for their antibacterial activities using the disk diffusion method. The EA-ME of three bacterial species, Planococcus sp., Klebsiella aerogenes, Enterococcus avium, from the pomegranate aphids Aphis punicae, Chrysoperia carnea, and Tapinoma magnum, respectively, exhibited elevated antibacterial activity against one or several of the five pathogenic bacteria tested. The inhibition zones ranged from 10.00 ± 0.13 to 20.00 ± 1.11 mm, with minimum inhibitory concentration (MIC) values ranging from 0.156 mg/mL to 1.25 mg/mL. The most notable antibacterial activity was found in the EA-ME of K. aerogenes against Klebsiella pneumonia and Escherichia coli, with an MIC value of 0.156 mg/mL. The cytotoxic activity of EA-ME was dependent on the cell line tested. The most significant cytotoxicity effect was observed for extracts of K. aerogenes and E. avium, at 12.5 µg/mL, against the epithelial cells of lung carcinoma (A549), with a cell reduction of 79.4% and 67.2%, respectively. For the EA-ME of K. aerogenes and Pantoea agglomerans at 12.5 µg/mL, 69.4% and 67.8% cell reduction were observed against human colon cancer (Hct116), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of three EA-ME revealed the presence of several bioactive secondary metabolites that have been reported previously to possess antibacterial and anticancer properties. To the best of our knowledge, this is the first study to examine the biological activities of endosymbiotic bacteria in aphids, aphid predators and ants. The promising data presented in this study may pave the way for alternative drugs to overcome the continued emergence of multidrug-resistant bacteria, and find alternative drugs to conventional cancer therapies.

Prokaryotic Communities from Pristine Cave Environments: Biotechnological Potential with Sustainable Production

Pristine environments, such as caves, are unique habitats that are isolated from human activity and are exposed to extreme environmental conditions. These environments are rich sources of microbial diversity, and the microorganisms that thrive in these conditions have developed unique survival skills. One such skill is the biosynthesis of secondary metabolites with potential bioactivities, which provide the organisms with a competitive advantage in these extreme environments. The isolation and characterization of microbial strains from the surfaces of pristine cave environments are important for exploring the biotechnological potential of these organisms. These studies can reveal new products with antibacterial, antifungal, anti-inflammatory, antioxidant, and anticancer activities, among others. In addition, the identification of specific compounds responsible for these biological activities can contribute to the development of new drugs and products for sustainable biotechnological applications. Recent developments in genomics, bioinformatics, chemoinformatics, metabolic engineering, and synthetic biology have opened new possibilities for drug discovery, making the exploration of bacterial secondary metabolites more promising. In recent years, several bacteria with bioactive potential have been described, and several compounds with bioactivity have been identified. These findings are essential for the development of new drugs and products for the benefit of society. This paper discusses the potential of microorganisms found in pristine cave surfaces as a source of new metabolites with bioactivity that could have sustainable biotechnological applications. The authors suggest that more research should be conducted in these environments to better understand the microorganisms and the biosynthesis of these metabolites and to identify new compounds and metabolic pathways that could be of interest for the development of new drugs and products. The aim is to highlight the importance of these habitats as a potential source of new bioactive compounds that could be used for sustainable biotechnological applications.