The comparative plastisphere microbial community profile at Kung Wiman beach unveils potential plastic-specific degrading microorganisms

Background

Plastic waste is a global environmental issue that impacts the well-being of humans, animals, plants, and microorganisms. Microplastic contamination has been previously reported at Kung Wiman Beach, located in Chanthaburi province along with the Eastern Gulf of Thailand. Our research aimed to study the microbial population of the sand and plastisphere and isolate microorganisms with potential plastic degradation activity.

Methods

Plastic and sand samples were collected from Kung Wiman Beach for microbial isolation on agar plates. The plastic samples were identified by Fourier-transform infrared spectroscopy. Plastic degradation properties were evaluated by observing the halo zone on mineral salts medium (MSM) supplemented with emulsified plastics, including polystyrene (PS), polylactic acid (PLA), polyvinyl chloride (PVC), and bis (2-hydroxyethyl) terephthalate (BHET). Bacteria and fungi were identified by analyzing nucleotide sequence analysis of the 16S rRNA and internal transcribed spacer (ITS) regions, respectively. 16S and ITS microbiomes analysis was conducted on the total DNA extracted from each sample to assess the microbial communities.

Results

Of 16 plastic samples, five were identified as polypropylene (PP), four as polystyrene (PS), four as polyethylene terephthalate (PET), two as high-density polyethylene (HDPE), and one sample remained unidentified. Only 27 bacterial and 38 fungal isolates were found to have the ability to degrade PLA or BHET on MSM agar. However, none showed degradation capabilities for PS or PVC on MSM agar. Notably, Planococcus sp. PP5 showed the highest hydrolysis capacity of 1.64 ± 0.12. The 16S rRNA analysis revealed 13 bacterial genera, with seven showing plastic degradation abilities: Salipiger, Planococcus, Psychrobacter, Shewanella, Jonesia, Bacillus, and Kocuria. This study reports, for the first time of the BHET-degrading properties of the genera Planococcus and Jonesia. Additionally, The ITS analysis identified nine fungal genera, five of which demonstrated plastic degradation abilities: Aspergillus, Penicillium, Peacilomyces, Absidia, and Cochliobolus. Microbial community composition analysis and linear discriminant analysis effect size revealed certain dominant microbial groups in the plastic and sand samples that were absent under culture-dependent conditions. Furthermore, 16S and ITS amplicon microbiome analysis revealed microbial groups were significantly different in the plastic and sand samples collected.

Conclusions

We reported on the microbial communities found on the plastisphere at Kung Wiman Beach and isolated and identified microbes with the capacity to degrade PLA and BHET.

Exploring untapped bacterial communities and potential polypropylene-degrading enzymes from mangrove sediment through metagenomics analysis

The versatility of plastic has resulted in huge amounts being consumed annually. Mismanagement of post-consumption plastic material has led to plastic waste pollution. Biodegradation of plastic by microorganisms has emerged as a potential solution to this problem. Therefore, this study aimed to investigate the microbial communities involved in the biodegradation of polypropylene (PP). Mangrove soil was enriched with virgin PP sheets or chemically pretreated PP comparing between 2 and 4 months enrichment to promote the growth of bacteria involved in PP biodegradation. The diversity of the resulting microbial communities was accessed through 16S metagenomic sequencing. The results indicated that Xanthomonadaceae, unclassified Gaiellales, and Nocardioidaceae were promoted during the enrichment. Additionally, shotgun metagenomics was used to investigate enzymes involved in plastic biodegradation. The results revealed the presence of various putative plastic-degrading enzymes in the mangrove soil, including alcohol dehydrogenase, aldehyde dehydrogenase, and alkane hydroxylase. The degradation of PP plastic was determined using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and Water Contact Angle measurements. The FTIR spectra showed a reduced peak intensity of enriched and pretreated PP compared to the control. SEM images revealed the presence of bacterial biofilms as well as cracks on the PP surface. Corresponding to the FTIR and SEM analysis, the water contact angle measurement indicated a decrease in the hydrophobicity of PP and pretreated PP surface during the enrichment.

Nonomuraea corallina sp. nov., isolated from coastal sediment in Samila Beach, Thailand: insights into secondary metabolite synthesis as anticancer potential

A novel marine actinomycete, designated strain MCN248T, was isolated from the coastal sediment in Songkhla Province, Thailand. Based on the 16S rRNA gene sequences, the new isolate was closely related to Nonomuraea harbinensis DSM45887T (99.2%) and Nonomuraea ferruginea DSM43553T (98.6%). Phylogenetic analyzes based on the 16S rRNA gene sequences showed that strain MCN248T was clustered with Nonomuraea harbinensis DSM45887T and Nonomuraea ferruginea DSM43553T. However, the digital DNA-DNA hybridization analyzes presented a low relatedness of 40.2% between strain MCN248T and the above closely related strains. This strain contained meso-diaminopimelic acid. The acyl type of the peptidoglycan was acetyl, and mycolic acids were absent. The major menaquinones were MK-9(H2) and MK-9(H4). The whole cell sugars consisted of madurose, ribose, mannose, and glucose. Diphosphatidylglycerol, hydroxyl-phosphatidylethanolamine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylglycerol were detected as the major phospholipids. The predominant cellular fatty acids were iso-C16:0 (40.4%), 10-methyl-C17:0 (22.1%), and C17:1ω 8c (10.9%). The DNA G + C content of the genomic DNA was 71.7%. With in silico analyzes, the antiSMASH platform uncovered a diverse 29 secondary metabolite biosynthesis arsenal, including non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) of strain MCN248T, with a high prevalence of gene cluster encoding pathways for the production of anticancer and cytotoxic compounds. Consistently, the crude extract could inhibit colorectal HCT-116 cancer cells at a final concentration of 50 μg/mL. Based on the polyphasic approach, strain MCN248 was designated as a novel species of the genus Nonomuraea, for which the name Nonomuraea corallina sp. nov. is proposed. The type strain of the type species is MCN248T (=NBRC115966T = TBRC17110T).

Bioactive Metabolites from Terrestrial and Marine Actinomycetes

Actinomycetes inhabit both terrestrial and marine ecosystems and are highly proficient in producing a wide range of natural products with diverse biological functions, including antitumor, immunosuppressive, antimicrobial, and antiviral activities. In this review, we delve into the life cycle, ecology, taxonomy, and classification of actinomycetes, as well as their varied bioactive metabolites recently discovered between 2015 and 2023. Additionally, we explore promising strategies to unveil and investigate new bioactive metabolites, encompassing genome mining, activation of silent genes through signal molecules, and co-cultivation approaches. By presenting this comprehensive and up-to-date review, we hope to offer a potential solution to uncover novel bioactive compounds with essential activities.

Amycolatopsis iheyensis sp. nov., isolated from soil on Iheya Island, Japan

A novel actinomycete, designated strain OK19-0408^T, was isolated from soil collected on Iheya island, Okinawa prefecture, Japan. Using the polyphasic taxonomic approach, comparing 16S rRNA gene sequences, the new isolate was found to be most closely related to Amycolatopsis vancoresmycina JCM12675^T (98.71 %). Phylogenetic analyses using 16S rRNA sequences indicated that strain OK19-0408^T was clustered with Amycolatopsis australiensis JCM15587^T. However, digital DNA-DNA hybridization analyses indicated a low relatedness, in the range of 33.9-34.7 %, between strain OK19-0408^T and these closely related strains. Strain OK19-0408^T contained meso-diaminopimelic acid and whole-cell sugars consisting of arabinose and galactose. The acyl type of the peptidoglycan was acetyl and mycolic acids were absent in strain OK19-0408^T. The major menaquinone was MK-9(H₄) and hydroxy-phosphatidylethanolamine was detected as the predominant phospholipid. The predominant cellular fatty acid was iso-C_16 : 0. The DNA G+C content of the genomic DNA was 71.5 mol%. Based on the polyphasic approach, strain OK19-0408^T represents a novel species of the genus Amycolatopsis, for which the name Amycolatopsis iheyensis sp. nov. is proposed. The type strain of the type species is OK19-0408^T (=NBRC115671^T=TBRC16040^T).

Plant growth-promoting properties of Streptomyces spp. isolates and their impact on mung bean plantlets’ rhizosphere microbiome

Phytophthora is an important, highly destructive pathogen of many plants, which causes considerable crop loss, especially durians in Thailand. In this study, we selectively isolated Streptomyces from the rhizosphere soil with a potent anti-oomycete activity against Phytophthora palmivora CbP03. Two strains (SNN087 and SNN289) demonstrated exceptional plant growth-promoting properties in pot experiment. Both strains promoted mung bean (Vigna radiate) growth effectively in both sterile and non-sterile soils. Metagenomic analysis revealed that Streptomyces sp. SNN289 may modify the rhizosphere microbial communities, especially promoting microbes beneficial for plant growth. The relative abundance of bacterial genera Bacillus, Sphingomonas, Arthrobacter, and Pseudarthrobacter, and fungal genera Coprinellus and Chaetomium were noticeably increased, whereas a genus Fusarium was slightly reduced. Interestingly, Streptomyces sp. SNN289 exhibited an exploratory growth, which allows it to survive in a highly competitive environment. Based on whole genome sequence analysis combined with an ANI and dDDH values, this strain should be classifiable as a new species. Functional annotation was also used to characterize plant-beneficial genes in SNN087 and SNN289 genomes for production of siderophores, 3-indole acetic acid (IAA), ammonia, and solubilized phosphate. AntiSMASH genome analysis and preliminary annotation revealed biosynthetic gene clusters with possible secondary metabolites. These findings emphasize the potential for application of strain SNN289 as a bioinoculant for sustainable agricultural practice.

Biosurfactant-Producing Bacillus velezensis PW192 as an Anti-Fungal Biocontrol Agent against Colletotrichum gloeosporioides and Colletotrichum musae

In this study, plant-root-associated Bacillus species were evaluated as antifungal biocontrol agents by analyzing the production of surface bioactive molecules known as lipopeptide biosurfactants. This study aimed to isolate and characterize antifungal biosurfactant-producing Bacillus bacterium. Bacillusvelezensis PW192 was isolated from the rhizosphere of Lagerstroemia macrocarpa var macrocarpa and identified based on phylogenetic analysis of the 16S rRNA gene. The biosurfactant was excreted to cultured supernatant and exhibited emulsification power up to 60% and a decrease in surface tension from 72 in distilled water to 21 mN/m. The surface tension properties were stable in a broad range of pH from 6 to 10, in high temperatures up to 100 °C, and in salinities with a NaCl concentration up to 12% (w/v). Starting from 0.5 mg of acid, precipitated crude biosurfactant exhibited antifungal activity toward Anthracnose, caused by the phytopathogens Colletotrichum gloeosporioides and C. musae. The chemical structures of the biosurfactant were structurally characterized as lipopeptides fengycin A and fengycin B. The stability of the biosurfactant, as well as the antifungal properties of B. velezensis PW192, can potentially make them useful as agricultural biocontrol agents, as well as in other biotechnological applications.

Micromonospora pelagivivens sp. nov., a new species of the genus Micromonospora isolated from deep-sea sediment in Japan

A novel marine actinomycete, designated strain KJ-029^T, was isolated from a marine sediment sample (water depth of 226 m) in Kagoshima, Japan. 16S rRNA gene sequence analysis revealed that the new isolate was most closely related to Micromonospora craniellae LHW 63014^T (99.3 % similarity). Phylogenetic analyses of the genus Micromonospora based on 16S rRNA gene sequences showed that strain KJ-029^T was clustered with Micromonospora craniellae LHW 63014^T and Micromonospora endophytica 202201^T. However, digital DNA-DNA hybridization analyses presented low levels of relatedness in the range of 24.8-32.9 % between strain KJ-029^T and the above closely related strains. The novel strain contained meso-diaminopimelic acid and 3-OH-diaminopimelic acid, d-glutamic acid, glycine and d-alanine in the cell-wall peptidoglycan. The acyl type of the peptidoglycan was glycolyl and mycolic acids were absent. The major menaquinone was MK-9(H₄). The whole-cell sugars consisted of glucose, mannose, xylose and ribose. Phosphatidylethanolamine was detected as the major phospholipid and corresponded to phospholipid type II. The predominant cellular fatty acid was iso-C_16 : 0. The DNA G+C content of the genomic DNA was 71.5 mol%. Based on the present polyphasic study, strain KJ-029^T represents a novel species of the genus Micromonospora, for which the name Micromonospora pelagivivens sp. nov. is proposed. The type strain is KJ-029^T (=NBRC 113519^T=TBRC 9233^T).

In vitro antiviral activity of spirotetronate compounds against dengue virus serotype 2

Spirotetronate compounds are polyketide secondary metabolites with diverse biological functions, such as antibacterial, antitumor and antiviral activities. Three pure spirotetronate compounds (2EPS-A, -B, -C) isolated from Actinomadura strain 2EPS showed inhibitory activity against dengue virus serotype 2 (DENV-2). 2EPS-A, -B and -C demonstrated the LC₅₀ values of 11.6, 27.5 and 12.0 μg/ml, respectively, in a test of cytotoxicity to Vero cells. The least cytotoxic, 2EPS-B, was further analyzed for its impact on viral propagation in a cell-based replication assay. At a concentration of 6.25 μg/ml, it could reduce the DENV-2 infection in Vero cells by about 94% when cells infected with DENV-2 were exposed to 2EPS-B, whereas direct treatment of DENV-2 with 2EPS-B at the same concentration prior to subsequent infection to Vero cell yielded no inhibition. 2EPS-A, -B an -C showed strong DENV-2 NS2B-NS3 protease inhibition in an in vitro assay, with IC₅₀ values of 1.94 ± 0.18, 1.47 ± 0.15 and 2.51 ± 0.21 μg/ml, respectively. Therefore, the spirotetronate compounds appear to prevent viral replication and viral assembly by inhibition of the viral protease.

Saccharopolyspora rhizosphaerae sp. nov., an actinomycete isolated from rhizosphere soil in Thailand

A novel actinomycete, designated as strain H219^T, was isolated from rhizosphere soil collected under an Elephant ear plant (Colocasiaesculenta) in Bangkok, Thailand. Strain H219^T was characterised using a polyphasic approach. Phylogenetic analysis of the 16S rRNA gene sequences revealed that this isolate was most closely related to Saccharopolyspora tripterygii JCM 32123^T (97.6 %), Saccharopolyspora dendranthemae NBRC 108675^T (97.5 %) and Saccharopolyspora flava NBRC 16345^T (97.5 %). However, DNA-DNA hybridization analyses showed a low relatedness in the range of 39-48 % between the novel isolate and the above closely related strains. The cell-wall peptidoglycan of strain H219^T contained meso-diaminopimelic acid. The diagnostic whole-cell sugars consisted of arabinose and galactose. The cellular fatty acid profile mainly comprised iso-C16 : 0, anteiso-C17 : 0, iso-C15 : 0, and 10-methyl C17 : 0. The major menaquinone was MK-9(H4). The detected phospholipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylethanolamine-containing hydroxylated fatty acids and an unknown phospholipid. The DNA G+C content was 70.6 mol%. Strain H219^T represented chemotaxonomic and morphological characteristics that were consistent with members of the genus Saccharopolyspora. However, strain H219^T could be distinguished from closely related strains by several phenotypic properties. Based on the data from the polyphasic studies, we propose that strain H219^T is a novel species within the genus Saccharopolyspora, Saccharopolysporarhizosphaerae sp. nov. The type strain is H219^T (=TBRC 8564^T=NBRC 113388^T).

Saccharomonospora colocasiae sp. nov., an actinomycete isolated from the rhizosphere of Colocasia esculenta

A non-Streptomyces actinomycete, designated as strain S265^T, was isolated from rhizosphere collected under an elephant ear plant (Colocasia esculenta) in Bangkok, Thailand. The taxonomic position of this strain was determined by a polyphasic approach. Strain S265^T formed single globose spores on long, branching, aerial hyphae. It produced abundant aerial mycelium with green colour. The cell wall contained meso-diaminopimelic acid, and diagnostic whole-cell sugars were arabinose and galactose. Phosphatidylethanolamine and diphosphatidylglycerol were detected predominantly as polar lipids, whereas mycolic acids were not found. The major menaquinone was MK-9(H4), and principal cellular fatty acids were C15 : 1 B, iso-C16 : 1 H, anteiso-C15 : 0 and C15 : 0 2-OH. The DNA G+C content was 69 mol%. According to phylogenetic analysis, strain S265^T was clustered with Saccharomonospora glauca K62^T (98.1 %) and Saccharomonosporaviridis DSM 43017^T (97.1 %) despite its 16S rRNA gene sequence showing the highest similarity value to that of Saccharomonosporaazurea NA-128^T (98.6 %). DNA-DNA relatedness values between strain S265^T and the closely related strains were in the range of 7-50 %, thus strengthening the evidence derived from the polyphasic study that strain S265^T represents a novel species within the genus Saccharomonospora, for which the name Saccharomonosporacolocasiae sp. nov. is proposed. The type strain is S265^T (=TBRC 7235^T=NBRC 112945^T).

1-Methoxypyrrole-2-carboxamide-A new pyrrole compound isolated from Streptomyces griseocarneus SWW368

A new pyrrole compound, 1-methoxypyrrole-2-carboxamide, was obtained from a culture broth of Streptomyces griseocarneus SWW368, which was isolated from the rhizospheric soil under a Para rubber tree (Hevea brasiliensis). The chemical structure was elucidated by 1D NMR, 2D NMR, and MS, as a pyrrole ring with a N-methoxy group and a primary amide group. It exhibited antibacterial properties against Kocuria rhizophila, Staphylococcus aureus and Xanthomonas campestris pv. oryzae; however, cytotoxicity of the compound at 714 μM against several mammalian tumor cell lines, i.e. A549, PANC1, HT29, HT1299 and HeLa S3, were not detected.

Thailandins A and B, New Polyene Macrolactone Compounds Isolated from Actinokineospora bangkokensis Strain 44EHW(T), Possessing Antifungal Activity against Anthracnose Fungi and Pathogenic Yeasts

Two new polyene macrolactone antibiotics, thailandins A, 1, and B, 2, were isolated from the fermentation broth of rhizosphere soil-associated Actinokineospora bangkokensis strain 44EHW(T). The new compounds from this strain were purified using semipreparative HPLC and Sephadex LH-20 gel filtration while following an antifungal activity guided fractionation. Their structures were elucidated through spectroscopic techniques including UV, HR-ESI-MS, and NMR. These compounds demonstrated broad spectrum antifungal activity against fungi causing anthracnose disease (Colletotrichum gloeosporioides DoA d0762, Colletotrichum gloeosporiodes DoA c1060, and Colletotrichum capsici DoA c1511) as well as pathogenic yeasts (Candida albicans MT 2013/1, Candida parasilopsis DKMU 434, and Cryptococcus neoformans MT 2013/2) with minimum inhibitory concentrations ranging between 16 and 32 μg/mL. This is the first report of polyene antibiotics produced by Actinokineospora species as bioactive compounds against anthracnose fungi and pathogenic yeast strains.

Characterization of a gamma-butyrolactone synthetase gene homologue (stcA) involved in bafilomycin production and aerial mycelium formation in Streptomyces sp. SBI034

Streptomyces SBI034 produces several bafilomycin derivatives. Its afsA homologue (stcA) and putative γ-butyrolactone receptor gene (stcB) were cloned. Construction of a stcA disruptant (stcA gene knockout) resulted in complete abolishment of all bafilomycin production. Electron microscopic analysis showed a defect of aerial mycelium formation and sporulation in the stcA disruptant. Restoration of all phenotypic defects and bafilomycin production was observed in a stcA complemented strain. Addition of exogenous γ-butyrolactone (GBL) extracted from the culture broth of the wild-type strain could stimulate the aerial mycelium and spore formation of the stcA disruptant. These results suggest that stcA plays a role in GBL-mediated regulation of bafilomycin biosynthesis and morphological development in Streptomyces strain SBI034.

Streptosporangium jomthongense sp. nov., an actinomycete isolated from rhizospheric soil and emendation of the genus Streptosporangium

A novel actinomycete, strain 30EHST, was isolated from the rhizospheric soil under an elephant ear plant (Caladium bicolor) in Jomthong district, Bangkok, Thailand. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 30EHST fell within the cluster of the genus Streptosporangium . Chemical composition analysis confirmed that the strain represented a member of the genus Streptosporangium even though this strain produced a tightly packed single spore on aerial hyphae. Phylogenetic analysis based on 16S rRNA gene sequences demonstrated that strain 30EHST was most closely related to Streptosporangium fragile NBRC 14311T (98.1 %), Streptosporangium carneum NBRC 15562T (97.8 %) and Streptosporangium violaceochromogenes NBRC 15560T (97.4 %). The DNA–DNA hybridization relatedness values between strain 30EHST and the above three strains were below 70 %. Based on combined data for phylogenetic analysis, DNA–DNA hybridization relatedness and physiological characteristics, it was concluded that strain 30EHST should be classified as representing a novel species of the genus Streptosporangium . We propose the name Streptosporangium jomthongense sp. nov., with the type strain 30EHST ( = BCC 53154T = NBRC 110047T). An emended description of the genus Streptosporangium is also proposed.

Actinokineospora bangkokensis sp. nov., isolated from rhizospheric soil

A novel actinomycete, strain 44EHWT, was isolated from rhizospheric soil under an Elephant ear plant (Colocasia esculenta) in Bangkok, Thailand. Strain 44EHWT produced long branching hyphae and abundant aerial mycelia with chains of rod-shaped spores. Whole-cell hydrolysates contained galactose, glucose, arabinose, ribose, mannose and rhamnose as diagnostic sugars. meso-Diaminopimelic acid was the diamino acid and glycine, alanine and glutamic acid were present in the cell-wall peptidoglycan with the acyl type of the peptidoglycan being acetyl. Phospholipids consisted of phosphatidylethanolamine, phosphatidylethanolamine with hydroxy fatty acids and diphosphatidylglycerol, as well as other unknown phospholipids; however, no mycolic acids were detected. The predominant menaquinone observed was MK-9(H4) and major fatty acids were iso-C16 : 0 and 2-OH iso-C16 : 0. The G+C content of genomic DNA was 74 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that this isolate was most similar to Actinokineospora enzanensis NBRC 16517T. However, DNA–DNA hybridization revealed a low relatedness between this isolate and A. enzanensis NBRC 16517T, indicating that this isolate represented a novel species in the genus Actinokineospora . On the basis of 16S rRNA gene sequence analysis, phenotypic characteristics and DNA–DNA hybridization data, we propose that strain 44EHWT represents a novel species in the genus Actinokineospora , Actinokineospora bangkokensis. The type strain is 44EHWT ( = BCC 53155T = NBRC 108932T).

Sarmentosamide, a novel hexadienamide from Thai soil actinomycetes

A new hexadienamide derivative named sarmentosamide (1) was identified from the culture of Streptomyces sp. SBI108 isolated from Thai soil under an herb. The structure was elucidated on the basis of spectroscopic data, and the absolute configuration was determined by chemical degradation.

Identification of actinomycetes from plant rhizospheric soils with inhibitory activity against Colletotrichum spp., the causative agent of anthracnose disease

BACKGROUND

Colletotrichum is one of the most widespread and important genus of plant pathogenic fungi worldwide. Various species of Colletotrichum are the causative agents of anthracnose disease in plants, which is a severe problem to agricultural crops particularly in Thailand. These phytopathogens are usually controlled using chemicals; however, the use of these agents can lead to environmental pollution. Potential non-chemical control strategies for anthracnose disease include the use of bacteria capable of producing anti-fungal compounds such as actinomycetes spp., that comprise a large group of filamentous, Gram positive bacteria from soil. The aim of this study was to isolate actinomycetes capable of inhibiting the growth of Colletotrichum spp, and to analyze the diversity of actinomycetes from plant rhizospheric soil.

RESULTS

A total of 304 actinomycetes were isolated and tested for their inhibitory activity against Colletotrichum gloeosporioides strains DoA d0762 and DoA c1060 and Colletotrichum capsici strain DoA c1511 which cause anthracnose disease as well as the non-pathogenic Saccharomyces cerevisiae strain IFO 10217. Most isolates (222 out of 304, 73.0%) were active against at least one indicator fungus or yeast. Fifty four (17.8%) were active against three anthracnose fungi and 17 (5.6%) could inhibit the growth of all three fungi and S. cerevisiae used in the test. Detailed analysis on 30 selected isolates from an orchard at Chanthaburi using the comparison of 16S rRNA gene sequences revealed that most of the isolates (87%) belong to the genus Streptomyces sp., while one each belongs to Saccharopolyspora (strain SB-2) and Nocardiopsis (strain CM-2) and two to Nocardia (strains BP-3 and LK-1). Strains LC-1, LC-4, JF-1, SC-1 and MG-1 exerted high inhibitory activity against all three anthracnose fungi and yeast. In addition, the organic solvent extracts prepared from these five strains inhibited conidial growth of the three indicator fungi. Preliminary analysis of crude extracts by high performance liquid chromatography (HPLC) indicated that the sample from strain JF-1 may contain a novel compound. Phylogenetic analysis revealed that this strain is closely related to Streptomyces cavurensis NRRL 2740 with 99.8% DNA homology of 16S rRNA gene (500 bp).

CONCLUSION

The present study suggests that rhizospheric soil is an attractive source for the discovery of a large number of actinomycetes with activity against Colletotrichum spp. An interesting strain (JF-1) with high inhibitory activity has the potential to produce a new compound that may be useful in the control of Colletotrichum spp.