Actinobacteria associated with Chinaberry tree are diverse and show antimicrobial activity

Mechanism of antibiotic resistance development in an activated sludge system under tetracycline pressure

The mechanism of antibiotic resistance (AR) development in an activated sludge system under tetracycline (TC) pressure was discussed and analyzed. According to the variation of macro-factors, including TC, COD, TN, TP, NH3-N, pH, heavy metals, and reactor settings, the tet genes respond accordingly. Consequently, the enrichment sites of tet genes form an invisible AR selection zone, where AR microorganisms thrive, gather, reproduce, and spread. The efflux pump genes tetA and tetB prefer anaerobic environment, while ribosome protective protein genes tetM, tetO, tetQ, tetT, and tetW were more concentrated in aerobic situations. As a corresponding micro-effect, different types of tet genes selected the corresponding dominant bacteria such as Thauera and Arthrobacter, suggesting the intrinsic relationship between tet genes and potential hosts. In summary, the macro-response and micro-effect of tet genes constitute an interactive mechanism with tet genes as the core, which is the crucial cause for the continuous development of AR. This study provides an executable strategy to control the development of AR in actual wastewater treatment plants from the perspective of macro-factors and micro-effects.

Genetic diversity, plant growth promotion potential, and antimicrobial activity of culturable endophytic actinobacteria isolated from Aconitum carmichaelii Debeaux

AIM

This study evaluated the phylogenetic diversity, plant growth promotion capacity, antifungal activity, and biocontrol potential of culturable actinobacterial endophytes isolated from the medicinal plant Aconitum carmichaelii Debeaux.

METHODS AND RESULTS

Isolation of actinobacteria from healthy A. carmichaelii plants was carried out on six different media. Full-length 16S rRNA gene was amplified by PCR from the genomic DNA of each strain. Indole-3-acetic acid and siderophore production were quantitatively assessed by the Salkowski and Chrome Azurol S methods, respectively. Rice seeds germination and seedling growth were employed to evaluate plant growth promotion capacities of candidate strains. Dual-culture assay and pot experiments were performed to investigate the antifungal and biocontrol potential of isolates. We obtained 129 actinobacterial isolates from A. carmichaelii, and they belonged to 49 species in 7 genera. These strains exhibited diverse plant growth promotion ability, among which one strain significantly enhanced rice seeds germination, while 31 strains significantly facilitated rice seedling growth. SWUST-123 showed strong antifungal activity against four pathogens in vitro and was most compatible with Qingchuan cultivar. SWUST-123 reduced around 40% of southern blight disease occurrence compared to blank control treatment. .

CONCLUSION

Aconitum carmichaelii harbored genetically diverse actinobacterial endophytes exhibiting diverse plant growth promotion and antifungal potential, some of which can be served as good candidates for biofertilizers and biocontrol agents.

A social niche breadth score reveals niche range strategies of generalists and specialists

Generalists can survive in many environments, whereas specialists are restricted to a single environment. Although a classical concept in ecology, niche breadth has remained challenging to quantify for microorganisms because it depends on an objective definition of the environment. Here, by defining the environment of a microorganism as the community it resides in, we integrated information from over 22,000 environmental sequencing samples to derive a quantitative measure of the niche, which we call social niche breadth. At the level of genera, we explored niche range strategies throughout the prokaryotic tree of life. We found that social generalists include opportunists that stochastically dominate local communities, whereas social specialists are stable but low in abundance. Social generalists have a more diverse and open pan-genome than social specialists, but we found no global correlation between social niche breadth and genome size. Instead, we observed two distinct evolutionary strategies, whereby specialists have relatively small genomes in habitats with low local diversity, but relatively large genomes in habitats with high local diversity. Together, our analysis shines data-driven light on microbial niche range strategies.

Root endophytic bacterial community composition of Aconitum carmichaelii debx. from three main producing areas in China

Aconitum carmichaelii Debx. is famous for the bioactive aconitum alkaloids as traditional Chinese medicine. Endophytic bacteria play vital roles in plant growth, health, and the production of secondary metabolites such as alkaloids. In this study, we employed 16 S rRNA amplicon high-throughput sequencing to determine the root endophytic bacterial community of A. carmichaelii Debx. collected from three main producing areas including the geo-authentic area in China, high performance liquid chromatography to measure the contents of six bioactive alkaloids and correlation analysis to explore the relationship among environmental factors, alkaloids contents, and endophytic bacterial community. The results indicated that the root core microbiota of A. carmichaelii Debx. was dominated by Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Root endophytic bacterial community in the geo-authentic area was distinct from the other two regions. Soil nitrogen contents, organic matter, and temperature were the main factors contributing to the endophytic bacterial community structure. Significant correlation was found between alkaloids contents and some bacterial genera. Particularly, the abundance of Lactobacillus was positively correlated with the contents of benzoyl-mesaconitine and benzoyl-aconine. This study provided the first insight into the root endophytic bacterial community composition of A. carmichaelii Debx., and can direct further isolation of functional bacterial strains.

Nitrogen fertilizer amount has minimal effect on rhizosphere bacterial diversity during different growth stages of peanut

The impact of short-term nitrogen fertilizer input on the structure and diversity of peanut rhizosphere microbiota (RM) at different growth stages (GSs) was explored in the southern paddy soil planting environment. Three levels of nitrogen were applied in the field: control (LN, 0 kg/hm²), medium nitrogen (MN, 55.68 kg/hm²), and high nitrogen (HN, 111.36 kg/hm²). The rhizosphere soil was collected during four GSs for high-throughput sequencing and chemical properties analysis. The effect of nitrogen fertilizer application on peanut RM was minimal and was obvious only at the seedling stage. In the four peanut GSs, a significant increase in relative abundance was observed for only one operational taxonomic unit (OTU) of Nitrospira under HN conditions at the seedling stage and mature stage, while there was no consistent change in other OTUs. The difference in RM among different peanut GSs was greater than that caused by the amount of nitrogen fertilizer. This may be due to the substantial differences in soil chemical properties (especially alkali-hydrolyzable nitrogen, pH, and available potassium or total potassium) among peanut GSs, as these significantly affected the RM structure. These results are of great value to facilitate deeper understanding of the effect of nitrogen fertilizer on peanut RM structure.

Changes of Endophytic Bacterial Community in Mature Leaves of Prunus laurocerasus L. during the Seasonal Transition from Winter Dormancy to Vegetative Growth

Diverse communities of bacterial endophytes inhabit plant tissues, and these bacteria play important roles for plant growth and health. Cherry laurel (Prunus laurocerasus L.) is a broadleaf evergreen shrub that is widely grown in temperate zones for its ornamental and medicinal properties, however virtually nothing is known about its associated bacterial community. In this study, we analysed the matured one-year-old leaves of this plant using Illumina-based 16S rRNA gene metabarcoding to reveal the community structure of endophytic bacteria and understand its shifts during the seasonal transition from winter dormancy to a spring vegetative state. The overall community was composed of four dominant phyla (Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes). Corynebacterium, Acinetobacter, and Chryseobacterium genera were the most prevalent bacteria, comprising 13.3%, 6.9%, and 6.8% of the amplicon sequence variants (ASVs), respectively. The ASV richness and diversity increased significantly in May as compared to other sampling months (February, March, and April). We observed high variation in the overall community structure of endophytic bacteria among collection dates. The variation was only reflected by a few core community members, suggesting that the changes of the endophytic community during winter/spring seasonal transition are mostly associated with the less abundant community members. We identified biomarker taxa for late winter, mid spring, and late spring collection dates. This study is the first one to report on the diversity and composition of bacterial endophytes in the leaves of cherry laurel and its shifts across the dormancy-to-vegetative seasonal transition.

Phylogenetic affiliation of endophytic actinobacteria associated with selected orchid species and their role in growth promotion and suppression of phytopathogens

Endophytic actinobacteria aid in plant development and disease resistance by boosting nutrient uptake or producing secondary metabolites. For the first time, we investigated the culturable endophytic actinobacteria associated with ten epiphytic orchid species of Assam, India. 51 morphologically distinct actinobacteria were recovered from surface sterilized roots and leaves of orchids and characterized based on different PGP and antifungal traits. According to the 16S rRNA gene sequence, these isolates were divided into six families and eight genera, where Streptomyces was most abundant (n=29, 56.86%), followed by Actinomadura, Nocardia, Nocardiopsis, Nocardioides, Pseudonocardia, Microbacterium, and Mycolicibacterium. Regarding PGP characteristics, 25 (49.01%) isolates demonstrated phosphate solubilization in the range of 61.1±4.4 - 289.7±11.9 µg/ml, whereas 27 (52.94%) isolates biosynthesized IAA in the range of 4.0 ± 0.08 - 43.8 ± 0.2 µg/ml, and 35 (68.62%) isolates generated ammonia in the range of 0.9 ± 0.1 - 5.9 ± 0.2 µmol/ml. These isolates also produced extracellular enzymes, viz. protease (43.13%), cellulase (23.52%), pectinase (21.56%), ACC deaminase (27.45%), and chitinase (37.25%). Out of 51 isolates, 27 (52.94%) showed antagonism against at least one test phytopathogen. In molecular screening, most isolates with antifungal and chitinase producing traits revealed the presence of 18 family chitinase genes. Two actinobacterial endophytes, Streptomyces sp. VCLA3 and Streptomyces sp. RVRA7 were ranked as the best strains based on PGP and antifungal activity on bonitur scale. GC-MS examination of ethyl acetate extract of these potent strains displayed antimicrobial compound phenol, 2,4-bis-(1,1-dimethylethyl) as the major metabolite along with other antifungal and plant growth beneficial bioactive chemicals. SEM analysis of fungal pathogen F. oxysporum (MTCC 4633) affected by Streptomyces sp. VCLA3 revealed significant destruction in the spore structure. An in vivo plant growth promotion experiment with VCLA3 and RVRA7 on chili plants exhibited statistically significant (p<0.05) improvements in all of the evaluated vegetative parameters compared to the control. Our research thus gives insight into the diversity, composition, and functional significance of endophytic actinobacteria associated with orchids. This research demonstrates that isolates with multiple plant development and broad-spectrum antifungal properties are beneficial for plant growth. They may provide a viable alternative to chemical fertilizers and pesticides and a sustainable solution for chemical inputs in agriculture.

Natural Products as Fungicide and Their Role in Crop Protection

Seeking solutions from nature for solving one and all problems is the age-old practice for mankind, and natural products are proved to be the most effective one for keeping up the balance of development as well as the “healthy, wealthy, and well” condition of mother nature. Fungal pathogens are proved to be a common and popular contaminant of agroecosystem that approximately causes 70–80% of total microbial crop loss. To meet the proper global increasing need of food products as a result of population explosion, managing agricultural system in an eco-friendly and profitable manner is the prime target; thus the word “sustainable agriculture” plays it part, and this package is highly effective when coupled with nature-derived fungicidal products that can minimize the event of fungal infections in agrarian ecosystem. Present study enlists the most common and effective natural products that might be of plant or microbial origin, their mode of action, day-by-day development of phytopathogenic resistance against the prevailing fungicides, and also their role in maintenance of sustainability of agricultural practices with special emphasis on their acceptance over the synthetic or chemical one. A large number of bioactive compounds ranging from direct plant (both cryptogams algae and moss and phanerogams)-derived natural extracts, essential oil of aromatic plants, and low-molecular-weight antimicrobial compounds known as phytoalexins to secondary metabolites that are both volatile and nonvolatile organic compounds of microbes (fungal and actinobacterial members) residing inside the host tissue, called endophyte, are widely used as agricultural bioweapons. The rhizospheric partners of plant, mycorrhizae, are also a prime agent of this chemical warfare and protect their green partners from fungal invaders and emphasize the concept of “sustainable agriculture.”

Comparison of the Analgesic and Anti-Inflammatory Effects of Xiaoyuningkun Decoction with Cynanchum Paniculatum and Fukeqianjin in a Mouse Model of Pelvic Inflammatory Disease

BACKGROUND Preclinical and clinical studies have shown that the extract of Cynanchum paniculatum (bunge) kitag and the fukeqianjin formulation have beneficial effects in pelvic inflammatory disease (PID). This study aimed to compare the effects of Cynanchum paniculatum and fukeqianjin with a new decoction, xiaoyuningkun, consisting of Melia toosendan, Angelica biserrata, and Cynanchum paniculatum, in a mouse model of PID. MATERIAL AND METHODS The mouse model of PID included injection of the upper genital tract with hydrochloric acid (HCl) and lipopolysaccharide (LPS). The control group underwent sham treatment with 0.9% physiological saline. Cynanchum paniculatum, fukeqianjin, and xiaoyuningkun decoction were administered orally for 15 days. Acetic acid-induced writhing and thermal nociception hot plate tests evaluated the analgesic effects of treatment. Mouse uterus and Fallopian tubes were examined histologically to evaluate the degree of inflammation. Immunohistochemistry was used to measure the protein expression of intercellular adhesion molecule-1 (ICAM-1) and vascular endothelial growth factor (VEGF). Enzyme-linked immunosorbent assay (ELISA) measured serum levels of inflammatory cytokines. RESULTS Treatment with xiaoyuningkun decoction significantly reduced the pain threshold in the mouse model of PID and the degree of inflammation in the uterus and Fallopian tubes compared with Cynanchum paniculatum and fukeqianjin. Cynanchum paniculatum decoction significantly reduced the serum levels of interleukin-1ß (IL-1ß), tumor necrosis factor-alpha (TNF-alpha), ICAM-1, and VEGF, and the expression of ICAM-1 and VEGF in the mouse uterus and Fallopian tubes. CONCLUSIONS The new xiaoyuningkun decoction had analgesic and anti-inflammatory effects in the mouse model of PID, possibly by inhibiting ICAM-1, VEGF, and inflammatory cytokines.