Myxobacteria and their products: current trends and future perspectives in industrial applications

Hyalangiumruber sp. nov, characterization of a novel myxobacterium strain s54d21 and their secondary metabolites

Myxobacteria are special bacteria with wide adaptability, which are rich sources of structurally diverse natural products with intriguing biological properties. Here, a gram-negative myxobacterium strain s54d21T was isolated from the sediment of a wetland park in China using the Escherichia coli baiting method. Based on 16S rRNA gene sequence and genomic data, the strain was demonstrated to be a novel species of a rare genus Hyalangium, designated Hyalangium ruber sp. nov (type strain s54d21T = GDMCC 1.1945T = JCM 39263T). The subsequent chemical investigation of the strain s54d21T led to the isolation of three rare 3,5,6-trisubstituted 2(1H)-pyrazinones, namely, hyalanones A-C (1-3), together with a known macrolactin A (4). Those new structures and their absolute configurations were unambiguously assigned by extensive analyses of spectroscopic data and density functional theory (DFT) calculations. In biological assays, compound 4 exhibited moderate cytotoxic activities against human cell lines RKO, A549, and NCM460 with IC50 values ranging from 27.21 to 32.14 μM.

Mining the soil myxobacteria and finding sources of anti-diabetic metabolites

Secondary metabolites produced by myxobacterial genera are often characterized as diverse molecules with unique structural properties which drove us to search for myxobacterial source of anti-diabetic drug discovery. In the present study, from 80 soil samples, out of sixty-five observed isolates, 30 and 16 were purified as Myxococcus and non-Myxococcus, respectively. Isolated strains taxonomically belonged to the genera Myxococcus, Corallococcus and Cystobacter, Archangium, Nanocystis, and Sorangium, and some could not be attributed. Secondary metabolites of selected non-Myxococcus isolates extracted by the liquid-liquid method showed that the myxobacterium UTMC 4530 demonstrated the highest inhibition on the formation of carbonyl group and fructosamine, respectively. In addition, it showed 23% and 15.8% inhibitory activity on α-glucosides and α-amylase compared to acarbose (23%, 18%), respectively. The extract of strain UTMC 4530 showed 35% induction effect on glucose adsorption while showing no radical scavenging activity and no toxic effect on HRBC lysis and HepG2 in cytotoxicity assays. The strain UTMC 4530 (ON808962), with the multiple antidiabetic activity, showed 87.3% similarity to Corallococcus llansteffanensis which indicates its affiliation to a new genus. The results of this study revealed that secondary metabolites produced by strain UTMC 4530 can be considered a promising source to find new therapeutic and pharmaceutical applications perhaps a multi-mechanism anti-diabetic compound.

Biogeographic distribution, assembly processes and potential nutrient cycling functions of myxobacteria communities in typical agricultural soils in China

Predatory myxobacteria are important soil micropredators with the potential to regulate soil microbial community structure and ecosystem function. However, the biogeographic distribution patterns, assembly processes, and potential nutrient cycling functions of myxobacteria communities in typical agricultural soils in China are still poorly understood. High-throughput sequencing, phylogenetic zero modeling, and the multi-nutrient cycling index were used to assess the biogeographic distribution, assembly processes, and soil ecosystem functions of predation myxobacteria communities in typical agricultural soils of six long-term fertilization ecological experimental stations. The results demonstrated a hump-shaped distribution of myxobacteria α-diversity along the latitudinal gradient and significant differences in myxobacteria β-diversity in typical agricultural soils (P < 0.05). Bacterial richness, soil organic carbon, and pH were the most important predictors of myxobacteria α-diversity, whereas geographic factors and soil pH were the most significant ecological predictors of myxobacteria β-diversity. Myxobacteria community assembly is dominated by deterministic processes, especially homogeneous selection, primarily driven by soil pH and bacterial richness. In addition, we revealed the ecological significance of myxobacteria communities in typical agricultural soil microbial networks and the potential link between myxobacteria communities and soil nutrient cycling. These findings enhance our understanding of the biogeographic distribution, community assembly, ecological predictors, and relationships with soil nutrient cycling of myxobacteria communities in typical agricultural soils, paving the way for a more predictive understanding of the effect of predatory myxobacteria communities on soil ecosystem function, which is essential for the development of sustainable agriculture.

Changes of endophytic microbial community in Rhododendron simsii roots under heat stress and its correlation with leaf physiological indicators

Introduction

The response mechanism of Rhododendron simsii and its endophytic microorganism to heat stress is still unclear.

Methods

The light incubator was used to set the temperature gradients, and the control (CK) was (day/night: 14/10 h) 25/22°C, the moderate-heat-stress (MHS) was 35/30°C and the high-heat-stress (HHS) was 40/35°C.

Results

Compared with CK, MHS significantly increased the contents of malondialdehyde, hydrogen peroxide, proline, and soluble sugar, as well as the activities of catalase and peroxidase in leaf, while HHS increased the activities of ascorbate peroxidase, and decreased chlorophyll content. Compared with CK, MHS reduced soil available nitrogen (N) content. Both heat stress changed the endophytic microbial community structure in roots. MHS enriched Pezicula and Paracoccus, while HHS significantly enriched Acidothermus and Haliangium. The abundance of Pezicula positively correlated with the contents of chlorophyll a and proline in leaf, and negatively correlated with soil ammonium N content. The abundance of Pezicula and Haliangium positively correlated with soluble sugar and malondialdehyde contents, respectively.

Conclusions

Our results suggest that root endophytic microorganisms play an important role in helping Rhododendron resisting heat stress, mainly by regulating soil N content and plant physiological characteristics.

The Predatory Myxobacterium Citreicoccus inhibens gen. nov. sp. nov. Showed Antifungal Activity and Bacteriolytic Property against Phytopathogens

The application and promotion of biological control agents are limited because of poor efficacy and unstable performance in the field. Screening microorganisms with high antagonistic activity, effective adaptability, and high field-survival should be prospected. Myxobacteria are soil predatory bacteria with wide adaptability, which are considered as good antagonists. Here, we report a myxobacterium strain M34 isolated from subtropical forest soil in South China using the Escherichia coli baiting method. Based on the morphological observation, physiological test, biochemical characteristics, 16S rRNA gene sequence, and genomic data, strain M34 was identified as a novel genus and novel species, representing a new clade of Myxococcaceae, for which the name Citreicoccus inhibens gen. nov. sp. nov. is proposed (type strain M34^T = GDMCC 1.2275^T = KCTC 82453^T). The typical features of M34, including fruiting body formation and extracellular fibrillar interconnection, indicated by microscopic observations, contributed to cell adaption in different environments. Furthermore, the strain showed antifungal activity against phytopathogenic fungi and predatory activity to both Gram-negative and Gram-positive phytopathogenic bacteria. The bioprotective mechanisms are attributed to the presence of pyrrolnitrin and derivative with antifungal activity and the extracellular proteins with lytic activity against pathogenic bacteria. Due to its multiple beneficial traits, strain M34 has the potential to be developed into a versatile biocontrol agent for the management of both fungal and bacterial phytopathogens.