Sinomonas humi sp. nov., an amylolytic actinobacterium isolated from mangrove forest soil

Sinomonas puerhi sp. nov. isolated from the rhizosphere soil of Pu-erh tea based on whole-genomic profiling

An aerobic, Gram-stain-positive, rod-shaped and non-motile bacterium, designated strain P10A9, was isolated from the rhizosphere soil of Pu-erh tea plants (Camellia sinensis var. assamica) in an organic tea garden in the Jingmai Pu-erh Tea District, Pu'er City, Yunnan Province, China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain P10A9 belongs to the genus Sinomonas, with its closest relative being Sinomonas atrocyanea KCTC 3377T (98.4% similarity). The major fatty acids (>10.0% of the total) were anteiso-C15 : 0 and anteiso-C17:0. The predominant respiratory quinone was MK-9(H2), with MK-8(H2) as a minor component. The major polar lipids included diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and glycolipids. The peptidoglycan contained glutamic acid (Glu), lysine (Lys), aspartic acid (Asp), serine (Ser), alanine (Ala) and glycine (Gly). The genome of strain P10A9 is 4.3 Mbp in size, with a G+C content of 69.2 mol%. Digital DNA-DNA hybridization values between strain P10A9 and other Sinomonas species ranged from 20.8 to 25.1%, and the average nucleotide identity values were significantly below the species delineation threshold (95-96%). Based on these results, strain P10A9 represents a novel species of the genus Sinomonas, for which the name Sinomonas puerhi sp. nov. is proposed. The type strain is P10A9T (=CCTCC AB 2024154T=KCTC 59368T).

Sinomonas gamaensis NEAU-HV1 remodels the IAA14-ARF7/19 interaction to promote plant growth

Sinomonas species typically reside in soils or the rhizosphere and can promote plant growth. Sinomonas enrichment in rhizospheric soils is positively correlated with increases in plant biomass. However, the growth promotion mechanisms regulated by Sinomonas remain unclear. By using soil systems, we studied the growth-promoting effects of Sinomonas gamaensis NEAU-HV1 on various plants. Through a combination of phenotypic analyses and microscopic observations, the effects of NEAU-HV1 on root development were evaluated. We subsequently conducted molecular and genetic experiments to reveal the mechanism promoting lateral root (LR) development. We demonstrated that NEAU-HV1 significantly promoted the growth of lettuce, wheat, maize, peanut and Arabidopsis. This effect was associated with multiple beneficial traits, including phosphate solubilization, indole-3-acetic acid and 1-aminocyclopropane-1-carboxylic acid deaminase production and survival ability in the rhizosphere and within the inner tissue of roots. In addition, NEAU-HV1 could secrete metabolites to promote LR development by affecting auxin transport and signaling. Importantly, we found that the influence of auxin signaling may be attributed to the remodeling interaction between SOLITARY-ROOT (SLR)/IAA14 and ARF7/19, occurring independently of the auxin receptor TIR1/AFB2. Our results indicate that NEAU-HV1-induced LR formation is dependent on direct remodeling interactions between transcription factors, providing novel insights into plant-microbe interactions.

Sinomonas terricola sp. nov., a plant-beneficial bacterium isolated from litchi rhizosphere soil in Guangdong, China

A novel plant-beneficial bacterium strain, designated as JGH33T, which inhibited Peronophythora litchii sporangia germination, was isolated on Reasoner's 2A medium from a litchi rhizosphere soil sample collected in Gaozhou City, Guangdong Province, PR China. Cells of strain JGH33T were Gram-stain-positive, aerobic, non-motile, bent rods. The strain grew optimally at 30-37 °C and pH 6.0-8.0. Sequence similarity analysis based on 16S rRNA genes indicated that strain JGH33T exhibited highest sequence similarity to Sinomonas albida LC13T (99.2 %). The genomic DNA G+C content of the isolate was 69.1 mol%. The genome of JGH33T was 4.7 Mbp in size with the average nucleotide identity value of 83.45 % to the most related reference strains, which is lower than the species delineation threshold of 95 %. The digital DNA-DNA hybridization of the isolate resulted in a relatedness value of 24.9 % with its closest neighbour. The predominant respiratory quinone of JGH33T was MK-9(H2). The major fatty acids were C15 : 0 anteiso (43.4 %), C16 : 0 iso (19.1 %) and C17 : 0 anteiso (19.3 %), and the featured component was C18 : 3 ω6c (1.01 %). The polar lipid composition of strain JGH33T included diphosphatidylglycerol, phosphatidylglycerol, dimannosylglyceride, phosphatidylinositol and glycolipids. On the basis of polyphasic taxonomy analyses data, strain JGH33T represents a novel species of the genus Sinomonas, for which the name Sinomonas terricola sp. nov. is proposed, with JGH33T (=JCM 35868T=GDMCC 1.3730T) as the type strain.

Sinomonas cellulolyticus sp. nov., isolated from Loktak lake

A novel cellulolytic strain JC656T was isolated from the rhizosphere soil of Alisma plantago-aquatica of floating island (Phumdis) of Loktak lake, Manipur, India. The 16S rRNA gene sequence similarities between strain JC656T and other Sinomonas type strains ranged between 98.5 and 97.3%, wherein strain JC656T exhibited the highest sequence similarity (98.5%) to Sinomonas notoginsengisoli KCTC 29237T. Colonies were yellow-colored and grew aerobically. Cells were gram-positive, rod-shaped and non-motile. The optimal growth of the strain JC656T occured at 28 °C and pH 7. Strain JC656T contained MK-9 as the predominant isoprenoid quinone and anteiso-C15:0, iso-C16:0 and anteiso-C17:0 as the major fatty acids. Diphosphatidylglycerol, phosphatidylinositol, phosphatidylglycerol, phosphatidylmonomethylethanolamine and a glycolipid were the polar lipids. Strain JC656T contained lysine, alanine, glutamine, diaminopimelic acid (DAP) and two unidentified amino acids as characteristic cell wall amino acids. The genome size of strain JC656T was 3.9 Mb with a DNA G + C content of 69.9 mol %. For the affirmation of the strain's taxonomic status, a detailed phylogenomic study was done. Based on its phylogenetic position and morphological, physiological, and genomic features, strain JC656T represents a new species of the genus Sinomonas, for which we propose the name Sinomonas cellulolyticus sp. nov. The type strain JC656T = (KCTC 49339T = NBRC 114142T).

Differential response of bacterial diversity and community composition to different tree ages of pomelo under red and paddy soils

Rhizosphere soil microbial communities substantially impact plant growth by regulating the nutrient cycle. However, dynamic changes in soil microbiota under different tree ages have received little attention. In this study, changes in soil physicochemical properties, as well as bacterial diversity and community structures (by high-throughput Illumina MiSeq sequencing), were explored in pomelo trees of different ages (i.e., 10, 20, and 30 years) under red and paddy soils cultivated by farmers with high fertilizer input. Moreover, soil factors that shape the bacterial community, such as soil pH, AP (available phosphorous), AK (available potassium), and AN (available nitrogen), were also investigated. Results showed that pH significantly decreased, while AP, AK, and AN increased with increasing tree age under red soil. For paddy soil, pH was not changed, while AP was significantly lower under 10-year-old pomelo trees, and AK and AN contents were minimum under 30-year-old pomelo trees. Both soil types were dominated by Proteobacteria, Acidobacteria, and Actinobacteria and showed contrasting patterns of relative abundance under different tree age groups. Bacterial richness and diversity decreased with increasing tree age in both soil types. Overall, bacterial community composition was different under different tree ages. RDA analysis showed that soil pH, AP, and AN in red soil, and pH and AP in paddy soil showed the most significant effects in changing the bacterial community structure. A random forest model showed Sinomonas and Streptacidiphilus in red soil, while Actinoallomurus and Microbacterium in paddy soil were the most important genera explaining the differences among different age groups. The ternary plot further revealed that genera enrichment for Age_30 was higher than that for Age_10 and Age_20 in red soil, whereas specific genera enrichment decreased with increasing tree age under paddy soil. Co-occurrence network revealed that bacterial species formed a complex network structure with increasing tree age, indicating a more stable microbial association under 20 and 30 years than 10-year-old pomelo trees. Hence, contrasting patterns of changes in soil physicochemical properties and soil microbial communities were recorded under different tree ages, and tree ages significantly affected the bacterial community structure and richness. These findings provide valuable information regarding the importance of microbes for the sustainable management of pomelo orchards by optimizing fertilizer input for different ages of trees.

Uncovering the biodiversity and biosynthetic potentials of rare actinomycetes

Background

Antibiotic resistance is on the rise, and new antibiotic research has slowed in recent years, necessitating the discovery of possibly novel microbial resources capable of producing bioactive compounds. Microbial infections are gaining resistance to existing antibiotics, emphasizing the need for novel medicinal molecules to be discovered as soon as possible. Because the possibilities of isolating undiscovered actinomycetes strains have decreased, the quest for novel products has shifted to rare actinomycetes genera from regular environments or the identification of new species identified in unusual habitats.

Main body of the abstract

The non-streptomyces actinobacteria are known as rare actinomycetes that are extremely difficult to cultivate. Rare actinomycetes are known to produce a variety of secondary metabolites with varying medicinal value. In this review, we reported the diversity of rare actinomycetes in several habitat including soil, plants, aquatic environment, caves, insects and extreme environments. We also reported some isolation methods to easily recover rare Actinobacteria from various sources guided with some procedures to identify the rare Actinobacteria isolates. Finally, we reported the biosynthetic potential of rare actinomycetes and its role in the production of unique secondary metabolites that could be used in medicine, agriculture, and industry. These microbial resources will be of interest to humanity, as antibiotics, insecticides, anticancer, antioxidants, to mention but a few.

Short conclusion

Rare actinomycetes are increasingly being investigated for new medicinal compounds that could help to address existing human health challenges such as newly emerging infectious illnesses, antibiotic resistance, and metabolic disorders. The bioactive secondary metabolites from uncommon actinomycetes are the subject of this review, which focuses on their diversity in different habitats, isolation, identification and biosynthetic potentials.

The Extremophilic Actinobacteria: From Microbes to Medicine

Actinobacteria constitute prolific sources of novel and vital bioactive metabolites for pharmaceutical utilization. In recent years, research has focused on exploring actinobacteria that thrive in extreme conditions to unearth their beneficial bioactive compounds for natural product drug discovery. Natural products have a significant role in resolving public health issues such as antibiotic resistance and cancer. The breakthrough of new technologies has overcome the difficulties in sampling and culturing extremophiles, leading to the outpouring of more studies on actinobacteria from extreme environments. This review focuses on the diversity and bioactive potentials/medically relevant biomolecules of extremophilic actinobacteria found from various unique and extreme niches. Actinobacteria possess an excellent capability to produce various enzymes and secondary metabolites to combat harsh conditions. In particular, a few strains have displayed substantial antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), shedding light on the development of MRSA-sensitive antibiotics. Several strains exhibited other prominent bioactivities such as antifungal, anti-HIV, anticancer, and anti-inflammation. By providing an overview of the recently found extremophilic actinobacteria and their important metabolites, we hope to enhance the understanding of their potential for the medical world.

Characterization of Sinomonas gamaensis sp. nov., a Novel Soil Bacterium with Antifungal Activity against Exserohilum turcicum

A novel Gram staining positive, aerobic bacterium NEAU-HV1^T that exhibits antifungal activity against Exserohilum turcicum was isolated from a soil collected from Gama, Hadjer lamis, Chad. It was grown at 10–45 °C (optimum 30 °C), pH 5–10 (optimum pH 8), and 0–4% (w/v) NaCl (optimum 1%). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain NEAU-HV1^T was closely related to Sinomonas susongensis A31^T (99.24% sequence similarity), Sinomonas humi MUSC 117^T (98.76%), and Sinomonas albida LC13^T (98.68%). The average nucleotide identity values between NEAU-HV1^T and its most closely related species were 79.34−85.49%. The digital DNA–DNA hybridization values between NEAU-HV1^T and S. susongensis A31^T, S. albida LC13^T, and S. humi MUSC 117^T were 23.20, 23.50, and 22.80%, respectively, again indicating that they belonged to different taxa. The genomic DNA G+C content was 67.64 mol%. The whole cell sugars contained galactose, mannose, and rhamnose. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, and four glycolipids. The respiratory quinone system comprised MK-9(H₂), MK-10(H₂), and MK-8(H₂). The major cellular fatty acids (>5%) were anteiso-C_15:0, anteiso-C_17:0, C_16:0, and iso-C_15:0. Based on the polyphasic analysis, it is suggested that the strain NEAU-HV1^T represents a novel species of the genus Sinomonas, for which the name Sinomonas gamaensis sp. nov. is proposed. The type strain is NEAU-HV1^T (= DSM 104514^T = CCTCC M 2017246^T).

Marine Rare Actinomycetes: A Promising Source of Structurally Diverse and Unique Novel Natural Products

Rare actinomycetes are prolific in the marine environment; however, knowledge about their diversity, distribution and biochemistry is limited. Marine rare actinomycetes represent a rather untapped source of chemically diverse secondary metabolites and novel bioactive compounds. In this review, we aim to summarize the present knowledge on the isolation, diversity, distribution and natural product discovery of marine rare actinomycetes reported from mid-2013 to 2017. A total of 97 new species, representing 9 novel genera and belonging to 27 families of marine rare actinomycetes have been reported, with the highest numbers of novel isolates from the families Pseudonocardiaceae, Demequinaceae, Micromonosporaceae and Nocardioidaceae. Additionally, this study reviewed 167 new bioactive compounds produced by 58 different rare actinomycete species representing 24 genera. Most of the compounds produced by the marine rare actinomycetes present antibacterial, antifungal, antiparasitic, anticancer or antimalarial activities. The highest numbers of natural products were derived from the genera Nocardiopsis, Micromonospora, Salinispora and Pseudonocardia. Members of the genus Micromonospora were revealed to be the richest source of chemically diverse and unique bioactive natural products.

Antibacterial, Anticancer and Neuroprotective Activities of Rare Actinobacteria from Mangrove Forest Soils

Mangrove is a complex ecosystem that contains diverse microbial communities, including rare actinobacteria with great potential to produce bioactive compounds. To date, bioactive compounds extracted from mangrove rare actinobacteria have demonstrated diverse biological activities. The discovery of three novel rare actinobacteria by polyphasic approach, namely Microbacterium mangrovi MUSC 115T, Sinomonas humi MUSC 117T and Monashia flava MUSC 78T from mangrove soils at Tanjung Lumpur, Peninsular Malaysia have led to the screening on antibacterial, anticancer and neuroprotective activities. A total of ten different panels of bacteria such as Methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, ATCC 70069, Pseudomonas aeruginosa NRBC 112582 and others were selected for antibacterial screening. Three different neuroprotective models (hypoxia, oxidative stress, dementia) were done using SHSY5Y neuronal cells while two human cancer cells lines, namely human colon cancer cell lines (HT-29) and human cervical carcinoma cell lines (Ca Ski) were utilized for anticancer activity. The result revealed that all extracts exhibited bacteriostatic effects on the bacteria tested. On the other hand, the neuroprotective studies demonstrated M. mangrovi MUSC 115T extract exhibited significant neuroprotective properties in oxidative stress and dementia model while the extract of strain M. flava MUSC 78T was able to protect the SHSY5Y neuronal cells in hypoxia model. Furthermore, the extracts of M. mangrovi MUSC 115T and M. flava MUSC 78T exhibited anticancer effect against Ca Ski cell line. The chemical analysis of the extracts through GC-MS revealed that the majority of the compounds present in all extracts are heterocyclic organic compound that could explain for the observed bioactivities. Therefore, the results obtained in this study suggested that rare actinobacteria discovered from mangrove environment could be potential sources of antibacterial, anticancer and neuroprotective agents.

Mangrove rare actinobacteria: taxonomy, natural compound, and discovery of bioactivity

Actinobacteria are one of the most important and efficient groups of natural metabolite producers. The genus Streptomyces have been recognized as prolific producers of useful natural compounds as they produced more than half of the naturally-occurring antibiotics isolated to-date and continue as the primary source of new bioactive compounds. Lately, Streptomyces groups isolated from different environments produced the same types of compound, possibly due to frequent genetic exchanges between species. As a result, there is a dramatic increase in demand to look for new compounds which have pharmacological properties from another group of Actinobacteria, known as rare actinobacteria; which is isolated from special environments such as mangrove. Recently, mangrove ecosystem is becoming a hot spot for studies of bioactivities and the discovery of natural products. Many novel compounds discovered from the novel rare actinobacteria have been proven as potential new drugs in medical and pharmaceutical industries such as antibiotics, antimicrobials, antibacterials, anticancer, and antifungals. This review article highlights the latest studies on the discovery of natural compounds from the novel mangrove rare actinobacteria and provides insight on the impact of these findings.

Sinomonas halotolerans sp. nov., an actinobacterium isolated from a soil sample

A novel actinobacterial strain, designated CFH S0499(T), was isolated from a soil sample collected from Catba island in Halong Bay, Vietnam. The cells were observed to be Gram-stain positive, aerobic, non-motile, curved rods. The strain was found to grow optimally at 28 °C and pH 7.0. Growth was found to occur at 0-7 % NaCl. Chemotaxonomically, the peptidoglycan type was determined to be of the A3α type, with glutamic acid, glycine, alanine and lysine as the major cell wall amino acids. The whole cell sugars were found to contain mannose, galactose, glucose, ribose and rhamnose. The polar lipids were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, glycolipids and two unidentified phospholipids. The major fatty acids were identified as anteiso-C15:0, iso-C15:0, anteiso-C17:0 and iso-C16:0 and the predominant respiratory quinone as MK-9 (H2), with a minor amount of MK-10 (H4) and MK-8 (H2). The G+C content of the genomic DNA was determined to be 71.8 mol%. The 16S rRNA gene sequence analysis showed that strain CFH S0499(T) should be assigned to the genus Sinomonas and is closely related to members of the species Sinomonas atrocyanea DSM 20127(T) (98.3 %), Sinomonas soli CW 59(T) (98.28 %), Sinomonas flava CW 108(T) (98.26 %), Sinomonas mesophila MPLK 26(T) (97.5 %) and Sinomonas notoginsengisoli SYP-B 575(T) (95.8 %). DNA-DNA hybridizations showed low values (49.1-54.5 %) between strain CFH S0499(T) and its four closest neighbours. Based on phenotypic, chemotaxonomic and phylogenetic analysis, strain CFH S0499(T) is concluded to represent a novel species of the genus Sinomonas, for which the name Sinomonas halotolerans sp. nov. is proposed, with CFH S0499(T) as the type strain (=CCTCC AB2014300(T) = KCTC 39116(T)).

Draft genome of amylolytic actinobacterium, Sinomonas humi MUSC 117(T) isolated from intertidal soil

The amylolytic actinobacterium, Sinomonas humi MUSC 117(T) was isolated from intertidal soil from Kuantan, Malaysia. MUSC 117(T) exhibited significant starch hydrolysis activity and was chosen for further analysis. Here we report approximately 4.4 Mbp high quality genome sequence of MUSC 117(T). Availability of the genome sequence will contribute to better understanding for the strain and allow further exploitation of its biotechnological potential.