Soil Actinobacteria Research Articles

Impacts of long-term different fertilization regimes on microbial utilization of straw-derived carbon in greenhouse vegetable soils: insights from its ecophysiological roles and temperature responses

As the largest organic carbon input in the agroecosystems, crop residues can increase soil carbon sequestration and crop production in greenhouse vegetable fields (GVFs). However, the soil microbiological mechanisms driving straw decomposition in GVFs under different incubation temperatures and fertilization treatments are not clear. Thus, soil samples were collected from a long-term field experiment included chemical fertilizer application alone (CF), 2/4 fertilizer N+2/4 organic fertilizer N (CM), 2/4 fertilizer N+1/4 organic fertilizer N+1/4 straw N (CMS), 2/4 fertilizer N+2/4 straw N (CS), and incubated with 13C-labeled straw at different temperatures (15, 25, and 35°C) for 60 days. Organic-amended treatments (CM, CMS, and CS), especially CMS treatment, increased soil bacterial Alpha diversity before and after straw addition. Straw decomposition process was dominated by soil Proteobacteria, Actinobacteria, and Firmicutes for each treatments. The effect of incubation temperature on soil microbial community composition was higher than that of fertilization treatments. Soil Alphaproteobacteria and Actinomycetia were the most predominant class involved in straw decomposition. Gammaproteobacteria (Pseudomonas, Steroidobacter, Acidibacter, and Arenimonas) were the unique and predominant class involved in straw decomposition at medium and high temperatures as well as in the straw-amended treatments. Organic-amended treatments, especially straw-amended treatments, increased the relative abundance of glycosyl transferases (GT) and auxiliary activities (AA). Alphaproteobacteria, Actinomycetia, and Gammaproteobacteria had higher relative contribution to carbohydrase genes. In summary, the long-term organic-amended treatments altered the structure of soil microbial communities and increased soil bacterial diversity, with the CMS having a greater potential to enhance resistance to external environmental changes. Soil Alphaproteobacteria and Actinomycetia were responsible for the dominance of straw decomposition, and Gammaproteobacteria may be responsible for the acceleration of straw decomposition. Fertilization treatments promote straw decomposition by increasing the abundance of indicator bacterial groups involved in straw decomposition, which is important for isolating key microbial species involved in straw decomposition under global warming.

Soil Actinobacteria Exhibit Metabolic Capabilities for Degrading the Toxic and Persistent Herbicide Metribuzin.

Metribuzin, a widely used triazine herbicide, persists in agricultural soils and poses significant environmental pollution threats globally. The aim of this study was to investigate the biodegradation of metribuzin by actinobacterial strains in vitro at different environmental conditions. From an initial screen of 12 actinobacterial strains, four bacteria exhibited robust growth in the presence of the metribuzin as the sole carbon source at 50 mg/L concentration. The optimization of metribuzin biodegradation under different conditions (pH, temperature and inoculum size) using a spectrophotometric method revealed that maximum degradation of metribuzin occurred at a pH of 7.2, a temperature 30 °C, and at an inoculum volume of 4%. Subsequent GC-MS validation confirmed the remarkable biodegradation capabilities of the actinobacterial isolates, where the strain C1 showed the highest rate of metribuzin degradation of 83.12%. Detailed phylogenetic identified the active strains as Streptomyces toxytricini (CH), Streptomyces stelliscabiei (B2), and two Streptomyces heliomycini (C1, C3). Structural analysis by ATR-FTIR spectroscopy confirmed the extensive biotransformation of the herbicide molecule. Our findings highlight the immense untapped potential of soil actinobacteria, particularly the Streptomyces heliomycini C1 strain, as versatile bioremediation agents for removing persistent agrochemical pollutants.

Water Management-Mediated Changes in the Rhizosphere and Bulk Soil Microbial Communities Alter Their Utilization of Urea-Derived Carbon.

As one of the most important fertilizers in agriculture, the fate of urea-derived nitrogen (urea-N) in agricultural ecosystems has been well documented. However, little is known about the function of urea-derived carbon (urea-C) in soil ecosystems, especially which soil microorganisms benefit most from the supply of urea-C and whether the utilization of urea-C by the rhizosphere and bulk soil microorganisms is affected by irrigation regimes. To address this, a soil pot experiment was conducted using 13C-labeled urea to investigate changes in the composition of the rhizosphere and bulk soil microbial communities and differences in the incorporation of urea-derived C into the rhizosphere and bulk soil phospholipid fatty acids (PLFA) pool under flooded irrigation (FI) and water-saving irrigation (CI). Our results suggest that the size and structure of the rhizosphere and bulk soil microbial communities were strongly influenced by the irrigation regime. The CI treatment significantly increased the total amount of PLFA in both the rhizosphere and bulk soil compared to the FI treatment, but it only significantly affected the abundance of Gram-positive bacteria (G+) in the bulk soil. In contrast, shifts in the microbial community structure induced by irrigation regimes were more pronounced in the rhizosphere soil than in the bulk soil. Compared to the FI treatment, the CI treatment significantly increased the relative abundances of the G+ and Actinobacteria in the rhizosphere soil (p < 0.05). According to the PLFA-SIP, most of the labeled urea-derived C was incorporated into 16:1ω7c, 16:0 and 18:1ω7c under both treatments. Despite these general trends, the pattern of 13C incorporation into the PLFA pool differed between the treatments. The factor loadings of individual PLFAs suggested that 18:1ω7c, 16:1ω7c and 16:1ω5c were relatively enriched in urea-C in the bulk soil, while 17:1ω8c, i16:0 and 16:0 were relatively enriched in urea-C in the rhizosphere soil under different irrigation regimes. The loadings also confirmed that 10-me16:0, cy17:0 and cy19:0 were relatively enriched in urea-C under the CI treatment, whereas 14:0, a15:0 and 15:0 were relatively enriched in urea-C under the FI treatment. These results are helpful not only in revealing the interception mechanism of urea-C in soil but also in understanding the functions of key microbes in element cycles.

Saccharopolyspora mangrovi sp. nov., a novel mangrove soil actinobacterium with distinct metabolic potential revealed by comparative genomic analysis.

A novel mangrove soil-derived actinomycete, strain S2-29T, was found to be most closely related to Saccharopolyspora karakumensis 5K548T based on 16S rRNA sequence (99.24% similarity) and genomic phylogenetic analyses. However, significant divergence in digital DNA-DNA hybridization, average nucleotide identity, and unique biosynthetic gene cluster possession distinguished S2-29T as a distinct Saccharopolyspora species. Pan genome evaluation revealed exceptional genomic flexibility in genus Saccharopolyspora, with > 95% accessory genome content. Strain S2-29T harbored 718 unique genes, largely implicated in energetic metabolisms, indicating different metabolic capacities from its close relatives. Several uncharacterized biosynthetic gene clusters in strain S2-29T highlighted the strain's untapped capacity to produce novel functional compounds with potential biotechnological applications. Designation as novel species Saccharopolyspora mangrovi sp. nov. (type strain S2-29T = JCM 34,548T = CGMCC 4.7716T) was warranted, expanding the known Saccharopolyspora diversity and ecology. The discovery of this mangrove-adapted strain advances understanding of the genus while highlighting an untapped source of chemical diversity.

Influences of the Integrated Rice-Crayfish Farming System with Different Stocking Densities on the Paddy Soil Microbiomes.

Integrated rice-fish farming has emerged as a novel agricultural production pattern to address global food security challenges. Aiming to determine the optimal, scientifically sound, and sustainable stocking density of red claw crayfish (Cherax quadricarinatus) in an integrated rice-crayfish farming system, we employed Illumina high-throughput 16S rRNA gene sequencing to evaluate the impact of different stocking densities of red claw crayfish on the composition, diversity, function, and co-occurrence network patterns of soil bacterial communities. The high stocking density of red claw crayfish reduced the diversity and evenness of the soil bacterial community during the mid-culture stage. Proteobacteria, Actinobacteria, and Chloroflexi emerged as the most prevalent phyla throughout the experimental period. Low stocking densities initially boosted the relative abundance of Actinobacteria in the paddy soil, while high densities did so during the middle and final stages. There were 90 distinct functional groups identified across all the paddy soil samples, with chemoheterotrophy and aerobic chemoheterotrophy being the most abundant. Low stocking densities initially favored these functional groups, whereas high densities enhanced their relative abundances in the later stages of cultivation. Medium stocking density of red claw crayfish led to a more complex bacterial community during the mid- and final culture stages. The experimental period showed significant correlations with soil bacterial communities, with total nitrogen (TN) and total phosphorus (TP) concentrations emerging as primary factors contributing to the alterations in soil bacterial communities. In summary, our findings demonstrated that integrated rice-crayfish farming significantly impacted the soil microbiomes and environmental factors at varying stocking densities. Our study contributed to theoretical insights into the profound impact of integrated rice-crayfish farming with various stocking densities on bacterial communities in paddy soils.

Spread of antibiotic-resistant actinobacteria in soils exposed to various types of anthropogenic impact

The work investigated the spectra of resistance to a certain set of antibiotics and the frequency of occurrence of resistant strains among typical soil bacteria – actinomycetes. Equal samples of isolates from sod-podzolic soil were used, selected at sites typifying various types of economic activity, namely: the production areas of a plywood factory and a chemical plant, the territory of a medical institution, and a solid waste collection and storage site. A total of 58 isolates with features characteristic of actinomycetes of the genus Streptomyces of the sections Cinereus, Helvolo-Flavus and Albus were obtained. It has been established that various types of economic activity lead to specific changes in the antibiotic resistance, which characterizes the soil of a natural grass-grass meadow (back-ground). Isolates with resistance to nalidixic acid, amoxicillin and ceftriaxone were found in the sample taken on the territory of the chemical plant more often than in the soil of the background site. The proportion of strains resistant to nalidixic acid, lincomycin and azithromycin was significantly (P&lt;0.05) higher in the soil samples taken at the MSW collection site and the territory of the medical institution, while those resistant to nalidixic acid and amoxicillin were in the sample from the plywood factory Groups of antibiotics (quinolones – nalidixic acid, and β-lactams – amoxicillin and ceftriaxone) were identified, the resistance to which in streptomyces isolates from soils involved in economic activity was significantly higher than in soil isolates from the background territory. The data obtained in the work indicate the need to monitor the spread of antibiotic resistance in soils that are not only at risk of accumulation of residual concentrations of antibiotics, but also other consequences of anthropogenic influences.

Potential of different species of actinobacteria in the management of Meloidogyne javanica.

Root-knot nematodes (RKN) are one of the most harmful soil-borne plant pathogens in the world. Actinobacteria are known phytopathogen control agents. The aim of this study was to select soil actinobacteria with control potential against the RKN (Meloidogyne javanica) in tomato plants and to determine mechanisms of action. Ten isolates were tested and a significant reduction was observed in the number of M. javanica eggs, and galls 46days after infestation with the nematode. The results could be explained by the combination of different mechanisms including parasitism and induction of plant defense response. The M. javanica eggs were parasited by all isolates tested. Some isolates reduced the penetration of juveniles into the roots. Other isolates using the split-root method were able to induce systemic defenses in tomato plants. The 4L isolate was selected for analysis of the expression of the plant defense genes TomLoxA, ACCO, PR1, and RBOH1. In plants treated with 4L isolate and M. javanica, there was a significant increase in the number of TomLoxA and ACCO gene transcripts. In plants treated only with M. javanica, only the expression of the RBOH1 and PR1 genes was induced in the first hours after infection. The isolates were identified using 16S rRNA gene sequencing as Streptomyces sp. (1A, 3F, 4L, 6O, 8S, 9T, and 10U), Kribbella sp. (5N), Kitasatospora sp. (2AE), and Lentzea sp. (7P). The efficacy of isolates from the Kitasatospora, Kribbella, and Lentzea genera was reported for the first time, and the efficacy of Streptomyces genus isolates for controlling M. javanica was confirmed. All the isolates tested in this study were efficient against RKN. This study provides the opportunity to investigate bacterial genera that have not yet been explored in the control of M. javanica in tomatoes and other crops.

Effects of Organic Matter Addition on Soil Carbon Contents, CO2 Emissions, and Bacterial Compositions in a Paddy Field in South China

Increasing soil organic carbon (SOC) contents and reducing carbon dioxide (CO2) emissions in paddy soil fields can result in positive impacts on climate change mitigation and soil quality. However, SOC accumulation and its microbial driving factors under enhanced fertilization strategies (e.g., organic matter application) are still unclear. Therefore, we investigated the effects of organic matter addition on SOC variations, CO2 fluxes, and their relationships with soil bacterial compositions and functions through a 6-year fertilizer experiment in rice fields involving two fertilization types, namely chemical fertilizer (NPK) and chemical fertilizer combined with organic matter (NPK+OM). The results showed significantly higher and lower SOC contents (p &lt; 0.05) in the 10–20 cm soil layer under the NPK+OM treatment before rice transplanting and after rice harvest, respectively, than those under the NPK treatment. The lower SOC contents after rice harvest might be due to the great nutrient consumption, resulting in higher rice yields in the NPK+OM than those in the NPK treatment by 6.68 to 32.35%. Compared with NPK, NPK+OM reduced the in-situ CO2 fluxes by 38.70–118.59%. However, the ex-situ SOC mineralization rates were not affected by NPK+OM in the 0–10 and 10–20 cm soil layers. The 16S rRNA sequence indicated a significant increase in the abundance of non-singleton amplicon sequence variants (ASVs) in the NPK+OM treatment scenario compared to those in the NPK treatment scenario. The top three most important soil bacterial phylum influenced by NPK+OM were LCP-89, BRC1, and Rokubacteria in April, as well as Firmicutes, Nitrospinae, and BRC1 in July. Soil Actinobacteria was negatively correlated with the SOC contents in April and July. The results of the present study demonstrate the economic and ecological benefits of the organic matter addition in rice production, as well as the contribution of soil bacteria to SOC accumulation and CO2 emission reduction.

Draft genome sequences of Arthrobacter sp. AZCC_0090 and Mycobacterium sp. AZCC_0083 isolated from oligotrophic subsurface forest soil in the Santa Catalina mountains of Southern Arizona.

Here, we present the genomes of two soil actinobacteria: Arthrobacter sp. strain AZCC_0090 and Mycobacterium sp. strain AZCC_0083, isolated from oligotrophic subsurface soils in Southern Arizona, USA.

Bioproduction and optimization of newly characterized melanin pigment from Streptomyces djakartensis NSS-3 with its anticancer, antimicrobial, and radioprotective properties

BackgroundMelanin is a natural pigment that is considered a promising biomaterial for numerous biotechnological applications across several industries. Melanin has biomedical applications as antimicrobial, anticancer, and antioxidant properties. Additionally, in the pharmaceutical and cosmetic industries, it is used in drug delivery and as a radioprotective agent. Also, melanin has environmental uses in the fields of bioremediation and the food industry. The biosynthesis of melanin pigment is an area of interest for researchers due to its multifunctionality, high compatibility, and biodegradability. Therefore, our present work is the first attempt to characterize and optimize the productivity of melanin pigment from Streptomyces djakartensis NSS-3 concerning its radioprotection and biological properties.ResultsForty isolates of soil actinobacteria were isolated from the Wadi Allaqui Biosphere Reserve, Egypt. Only one isolate, ACT3, produced a dark brown melanin pigment extracellularly. This isolate was identified according to phenotypic properties and molecular phylogenetic analysis as Streptomyces djakartensis NSS-3 with accession number OP912881. Plackett–Burman experimental design (PBD) and response surface methodology (RSM) using a Box-Behnken design (BBD) were performed for optimum medium and culturing conditions for maximum pigment production, resulting in a 4.19-fold improvement in melanin production (118.73 mg/10 mL). The extracted melanin pigment was purified and characterized as belonging to nitrogen-free pyomelanin based on ultraviolet–visible spectrophotometry (UV–VIS), Fourier transform infrared (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and NMR studies. Purified melanin demonstrated potent scavenging activity with IC50 values of 18.03 µg/mL and revealed high potency as sunscreens (in vitro SPF = 18.5). Moreover, it showed a nontoxic effect on a normal cell line (WI38), while it had a concentration-dependent anticancer effect on HCT116, HEPG, and MCF7 cell lines with IC50 = 108.9, 43.83, and 81.99 µg/mL, respectively. Also, purified melanin had a detrimental effect on the tested MDR bacterial strains, of which PA-09 and SA-04 were clearly more susceptible to melanin compared with other strains with MICs of 6.25 and 25 µg/mL, respectively.ConclusionOur results demonstrated that the newly characterized pyomelanin from Streptomyces djakartensis NSS-3 has valuable biological properties due to its potential photoprotective, antioxidant, anticancer, antimicrobial, and lack of cytotoxic activities, which open up new prospects for using this natural melanin pigment in various biotechnological applications and avoiding chemical-based drugs.

Разнообразие актинобактериальных сообществ в местах захоронения жидких отходов химического предприятия

The composition and taxonomic structure of the phylum Actinobacteria were studied on the example of technosols formed on the territory of the former tailings of liquid waste of a chemical enterprise in the floodplain of the Vyatka River. The diversity of actinobacteria in soil samples taken from three spatially remote monitoring sites (SG, SU1 and SU2), differing in the complex of physico-chemical properties and the nature of the vegetation cover, was studied. The results were compared with the background soil (BS) – alluvial soil selected on the territory of the Nurgush State Nature Reserve. The studies were carried out using high-performance sequencing using Illumina technology and the culture method (seeding). The culture method revealed representatives of the genera Streptomyces, Micromonospora, Streptosporangium and a number of oligospore forms in the actinobacterial complexes. The total number of actinomycetes in the samples of technosols varied from 2.4·104 to 1.8·105 CFU/g, and in the background soil was 8.5·103 CFU/g. Families of actinomycetes established by the seeding method were also detected using the amplicon sequencing of the V4 section of the 16S rRNA gene, but the molecular method made it possible to identify a number of other taxa in the studied samples, including those that do not have cultured representatives or are not yet classified. Using amplicon sequencing, it was found that representatives of the phylum Actinobacteria in samples of technogenically disturbed soils are absolute dominants in relative abundance in the total bacterial diversity. The proportion of actinobacteria in disturbed soils ranges from 33 to 41%, while in the background soil it is only 22%. Actinobacteria in the samples of technosols were represented by the families Micromonosporaceae, Micrococcaceae, Nocardioidaceae, Microbacteriaceae, Thermomonosporaceae, Pseudonocardiaceae, Actinosynnemataceae, and Intrasporangiaceae, etc. The taxonomic spectrum of actinobacteria in the BS sample was similar to technosols, but the proportion of taxa was different. The results obtained will be used in further studies of soil actinobiota in connection with changes in ecosystems disrupted by human economic activity, and are also of interest for the search and isolation of natural strains of actinobacteria for biotechnology purposes.

Evaluation of heavy metal removal and antibiofilm efficiency of biologically synthesized chitosan- silver Nano-bio composite by a soil actinobacterium Glutamicibacter uratoxydans VRAK 24

Biological synthesis of nanoparticles is cost-effective as well as safer than physical and chemical methods. This study focuses on the biological synthesis of silver nanoparticles using Glutamicibacter uratoxydans which remains still unexplored. The synthesized silver nanoparticles are encapsulated with chitosan to prepare nanobiocomposite. Actinobacteria were isolated from mesophilic soil and screened for heavy metal resistance. The potent heavy metal resistant isolate was identified by 16SrRNA sequencing and used for the biological synthesis of silver particles. The characterization of chitosan- silver nano-bio composite was carried out by UV–Vis spectroscopy, FTIR spectroscopy, and XRD. Morphology was analyzed by scanning electron microscopy. The particle size and stability were studied using Dynamic light scattering and Zeta potential analysis. The nano-bio composite was tested for lead removal efficiency and antibiofilm activity. The potent isolate was identified as Glutamicibacter uratoxydans and it was named as Glutamicibacter uratoxydans VRAK 24. The UV spectra showed maximum absorbance at 410 nm. The FTIR spectra and XRD confirmed chitosan encapsulation with silver nanoparticle. The size of nanobiocomposite was found to be 0.376. The stability of nanobiocomposite recorded a zeta potential value of −5.37 mV. The lead removal efficiency was found to be 87.69 %. In addition, the nanobiocomposite exhibited highest anti-biofilm activity against S.aureus when compared to E.coli. The research findings, concluded that the synthesized nanobiocomposite showed better anti-biofilm activity. Also, nanobiocomposite was found to be a good adsorbent for the removal of heavy metal lead.

In Vitro Coinoculation Between Actinobacteria and Diazotrophic Nodulating Bacteria from the Semiarid

Purpose: To evaluate the potential of actinobacterial strains from the Brazilian semiarid to establish facilitation relationships with native rhizobia from the same region. Theoretical framework: The study is based on the ecological and biotechnological importance of soil actinobacteria, producers of biosurfactants and enzymes, and of nitrogen-fixing rhizobia in legumes. Method: 50 strains of actinobacteria were isolated from soils from Ceará with different levels of anthropization and 19 strains of rhizobia using cowpea. The morphological, cultural and micromorphological characterization of the strains was performed, as well as the evaluation of their enzymatic profiles. In vitro facilitation tests were conducted between cellulolytic actinobacteria and non-cellulolytic rhizobia. Results: The soil areas presented a similar composition of actinobacteria, but strains from the anthropized area showed higher enzymatic activity. Two Streptomyces strains promoted the growth of non-cellulolytic rhizobia in vitro, indicating potential application as bioinoculants in microbial consortia. Conclusions: The study contributes to the knowledge of the interaction between beneficial microbial groups from the semiarid region and their possible biotechnological use in agriculture. Originality/value: Works on coinoculation between actinobacteria and rhizobia from semiarid soils are scarce.

Exploring Antibacterial Properties of Bioactive Compounds Isolated from Streptomyces sp. in Bamboo Rhizosphere Soil.

The increasing concern over multidrug resistance in pathogens has led to an ongoing search for novel antibiotics derived from soil actinobacteria. In this current investigation, actinobacteria were isolated from the rhizosphere of bamboo plants collected within the Megamalai forest of the Western Ghats in the Theni zone of Tamil Nadu, India. These actinobacteria were subjected to characterization, and their growth conditions were optimized to enhance the production of bioactive compounds. To assess antibacterial properties, the isolated Actinobacteria underwent testing using the agar plug method. The strain exhibiting notable antibacterial activity underwent further characterization through 16s rRNA gene sequencing and subsequent phylogenetic analysis. Employing response surface methodology (RSM), cultural conditions were fine-tuned. Bioactive compounds were extracted from the culture medium using ethyl acetate, and their antibacterial and antioxidant effects were evaluated through disc diffusion and DPPH radical scavenging methods, respectively. Ethyl acetate extracts were analyzed by using FT-IR and GC-MS techniques. In total, nine strains of Actinobacteria were isolated from the rhizosphere soil of bamboo. Among these, strain BS-16 displayed remarkable antibacterial activity against three strains: Staphylococcus aureus (19 mm), Bacillus subtilis (12 mm), and Streptococcus pyogenes (10 mm). This strain was identified as Streptomyces sp. The optimal conditions for bioactive compound production were determined as follows: malt extract (10 g), yeast extract (5 g), dextrose (5 g), pH 6.5, and temperature 30 °C. After a 7-day incubation period, the results showed a 6% increase in production. The ethyl acetate fraction derived from strain BS-16 exhibited dose-dependent antibacterial and antioxidant activities. FT-IR and GC-MS analyses revealed the presence of active compounds with antibacterial effects within the extract. Consequently, further investigation into the BS-16 strain holds promise for scaling up the production of bioactive compounds possessing antibacterial and antioxidant properties.

In Vitro Coinoculation Between Actinobacteria and Diazotrophic Nodulating Bacteria from the Semiarid

Purpose: To evaluate the potential of actinobacterial strains from the Brazilian semiarid to establish facilitation relationships with native rhizobia from the same region.&#x0D; &#x0D; Theoretical framework: The study is based on the ecological and biotechnological importance of soil actinobacteria, producers of biosurfactants and enzymes, and of nitrogen-fixing rhizobia in legumes.&#x0D; &#x0D; Method: 50 strains of actinobacteria were isolated from soils from Ceará with different levels of anthropization and 19 strains of rhizobia using cowpea. The morphological, cultural and micromorphological characterization of the strains was performed, as well as the evaluation of their enzymatic profiles. In vitro facilitation tests were conducted between cellulolytic actinobacteria and non-cellulolytic rhizobia.&#x0D; &#x0D; Results: The soil areas presented a similar composition of actinobacteria, but strains from the anthropized area showed higher enzymatic activity. Two Streptomyces strains promoted the growth of non-cellulolytic rhizobia in vitro, indicating potential application as bioinoculants in microbial consortia.&#x0D; &#x0D; Conclusions: The study contributes to the knowledge of the interaction between beneficial microbial groups from the semiarid region and their possible biotechnological use in agriculture.&#x0D; &#x0D; Originality/value: Works on coinoculation between actinobacteria and rhizobia from semiarid soils are scarce.

Control effect of root exudates from mycorrhizal watermelon seedlings on Fusarium wilt and the bacterial community in continuously cropped soil.

Watermelon (Citrullus lanatus) is susceptible to wilt disease caused by Fusarium oxysporum f. sp niveum (FON). AMF colonization alleviates watermelon wilt and regulates the composition of root exudates, but the effects of mycorrhizal watermelon root exudates on watermelon Fusarium wilt is not well understood. Root exudates of watermelon inoculated with AMF (Funeliformis mosseae or Glomus versiformme) were collected in this study. Then the root exudates of control plants and mycorrhizal plants were used to irrigate watermelon in continuous cropping soil, respectively. Meanwhile, the watermelon growth, antioxidant enzyme activity, rhizosphere soil enzyme activities and bacterial community composition, as well as the control effect on FON were analyzed. The results indicated that mycorrhizal watermelon root exudates promoted the growth of watermelon seedlings and increased soil enzyme activities, actinomyces, and the quantity of bacteria in rhizosphere soil. The proportion of Proteobacteria and Bacteroides was decreased, and the proportion of Actinobacteria, Firmicutes, and Chloroflexi in rhizosphere soil was increased when the seedlings were watered with high concentrations of mycorrhizal root exudates. The dominant bacterial genera in rhizosphere soil were Kaistobacter, Rhodanobacter, Thermomonas, Devosia, and Bacillus. The root exudates of mycorrhizal watermelon could reduce the disease index of Fusarium wilt by 6.7-30%, and five ml/L of watermelon root exudates inoculated with F. mosseae had the strongest inhibitory effect on watermelon Fusarium wilt. Our results suggest mycorrhizal watermelon root exudates changed the composition of bacteria and soil enzyme activities in rhizosphere soil, which increase the resistance of watermelon to Fusarium wilt and promoted the growth of plants in continuous cropping soil.

Emycin-E purified from Streptomyces sp. RG1011 from Himalayan soil has antibiofilm activity against Staphylococcus aureus

BackgroundStaphylococcus aureus is an opportunistic pathogen that causes deadly infections in human as well as animals. The intricate network of virulence factors and biofilms are the major hindrance for the antibiotics in the successful treatment of the infection. The aim of this study is to isolate, identify and characterize natural antimicrobial agent against S. aureus from natural resources. MethodsHimalayan soils were subjected to primary, secondary and tertiary screening to isolate soil Actinobacteria. Identification and characterization of the isolate was done by various biochemical assays and 16s rDNA sequencing. Partial purification of the potent antimicrobial agent was done by n-butanol from the culture supernatant, TLC and HPLC were performed to purify the active component and subjected to FTIR and ESI-MS analysis. ResultsThe potent isolate RM-1(13) was confirmed as Streptomyces griseus strain RG1011 (NCBI accession no: 0M780275) by biochemical and molecular analysis. The partially purified antimicrobial agent was active against various Gram-positive and Gram-negative pathogens. The active component was purified by HPLC and identified as Emycin-E by ESI-MS analysis. The Emycin-E has calculated MIC of 0.31 μg/ml against S. aureus ATCC 25923. Emycin-E inhibits the biofilm formation of S. aureus in in vitro microtiter plate assay. ConclusionsThe identified antimicrobial agent was found active against various Gram-positive and Gram-negative pathogens. We have successfully identified the active compound as Emycin-E by FTIR and ESI-MS analysis. Our study suggests the role of Emycin-E in the inhibition of biofilm formation in S. aureus.

Taxonomic and ecophysiological characteristics of actinobacteria in soils of the dry steppe zone of the Selenga Highlands (Western Transbaikalia).

Arid habitats have recently attracted increasing attention in terms of biodiversity research and the discovery of new bacterial species. These habitats are among the target ecosystems suitable for isolating new strains of actinobacteria that are likely to produce new metabolites. This paper presents the results on the isolation of actinobacteria from soils of the dry steppe zone of the Selenga Highlands, the characterization of their taxonomic diversity, as well as ecological and trophic properties. The bacterial counts on ISP 4 medium ranged from 6.6 × 105 to 7.1 × 106 CFU/g. The highest bacterial counts were observed in the subsurface and middle horizons of the studied soils. 28 strains of Gram-positive bacteria represented by thin-branched mycelium, coccoid and bacilliform forms were isolated. According to the results of 16S rRNA gene analysis, the isolated strains were representatives of Streptomyces, Arthrobacter, Glycomyces, Kocuria, Microbacterium, Micromonospora, Nocardioides, Pseudarthrobacter, and Rhodococcus (Actinomycetota). One isolate that showed low 16S rRNA gene sequence similarity with previously isolated and validly described species was a new species of the genus Glycomyces. It was shown that all tested strains are mesophilic, prefer neutral or slightly alkaline conditions, have growth limits in the temperature range of 5-45 °C and pH 6-9. The optimal NaCl concentration for growth of most strains was 0-1 %. The strains under study were capable of utilizing a wide range of mono- and disaccharides and polyatomic alcohols as a carbon source. The isolated strains were capable of using both organic (proteins and amino acids) and inorganic (ammonium salts and nitrates) compounds as nitrogen sources. The examinations of extracellular enzymes showed that all isolates were capable of producing catalase and amylase; 78.6 % of the total number of isolates produced protease and lipase; 53.6 %, cellulase; and 28.6 %, urease. The data obtained expand current knowledge about the diversity of microbial communities in soils of the Selenga Highlands and also confirm the potential of searching for new actinobacteria species in these soils.

Экологические особенности и биотехнологические возможности почвенных актинобактерий (обзор)

Actinobacteria are gram-positive aerobic and facultative anaerobic bacteria that tend to form branching hyphae capable of developing into mycelium. Their main role is in the decomposition of complex polymers in the soil: lignin, cellulose, chitin, humus substances; fertility formation; production of antibiotic substances; accumulation of biologically active compounds. Actinobacteria secrete into the environment a complex of secondary exometabolites of various compositions with aliphatic, carbocyclic, heterocyclic, nitrogenous, oxygen-containing and sulfur-containing compounds. Most of the isolated secondary metabolites have antibiotic, antimicrobial, antiviral, herbicidal, insecticidal properties. Biotechnological capabilities of soil actinobacteria producing biologically active substances with a wide range of environmental effects are used in the development of multifunctional biologics for various industries. Actinobacteria play a crucial role in optimizing the growing conditions of plants, and therefore there is a natural interest in studying the factors that influence the relationship between actinobacteria and various crops in specific soil conditions. The development of this issue is an important link in the ecological characterization of the soil microbial complex and it will help to develop the theoretical foundations for the targeted regulation of the interactions of actinobacteria with phytopathogenic microorganisms and insect pests. The purpose of this work is to analyze the ecological features and biotechnological capabilities of soil actinobacteria. The review describes the distribution of actinobacteria in various types of soils, including those with the presence of pollutant; the composition of the metabolites produced; relationships with other microorganisms, as well as biotechnological properties and the possibility of using actinobacteria for the development of biological products for agroecosystems.

Response of Bacterial Communities to Heavy Metal Contamination in an Abandoned Chromate Factory

The chromium slags left by industry emission has caused serious damage to the local ecological environment, and microorganisms were sensitive to the variation in the surrounding environmental factors. In this work, 14 soil samples around an abandoned chromate factory were collected. We utilized the 16S rRNA regions from soil DNA to explore the possible effects of environmental factors on soil bacterial communities. High-throughput DNA sequencing results suggested that bacterial communities varied greatly from different soil samples, but Actinobacteria and Proteobacteria were predominant in all samples in the phylum level. In addition, Pseudarthrobacter, Thiobacillus, Paenisporosarcina, Sphingomonas, and Bacillus were abundant at a more refined species level. Based on redundancy analysis (RDA) and variation partitioning analysis (VPA), the results revealed that pH value, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), chromium (Cr) and lead (Pb) could obviously affect the bacterial community structure. Heavy metals, soil nutrients, and pH could explain 37.69%, 13.61%, and 31.41% of bacterial community variation, respectively. This study would provide a theoretical basis for future remediation of local Cr-contaminated soil.