Plantactinosporasoyae sp. nov., an endophytic actinomycete isolated from soybean root [Glycine max (L.) Merr]

Plant endophytes: unveiling hidden applications toward agro-environment sustainability

Endophytic microbes are plant-associated microorganisms that reside in the interior tissue of plants without causing damage to the host plant. Endophytic microbes can boost the availability of nutrient for plant by using a variety of mechanisms such as fixing nitrogen, solubilizing phosphorus, potassium, and zinc, and producing siderophores, ammonia, hydrogen cyanide, and phytohormones that help plant for growth and protection against various abiotic and biotic stresses. The microbial endophytes have attained the mechanism of producing various hydrolytic enzymes such as cellulase, pectinase, xylanase, amylase, gelatinase, and bioactive compounds for plant growth promotion and protection. The efficient plant growth promoting endophytic microbes could be used as an alternative of chemical fertilizers for agro-environmental sustainability. Endophytic microbes belong to different phyla including Euryarchaeota, Ascomycota, Basidiomycota, Mucoromycota, Firmicutes, Proteobacteria, and Actinobacteria. The most pre-dominant group of bacteria belongs to Proteobacteria including α-, β-, γ-, and δ-Proteobacteria. The least diversity of the endophytic microbes have been revealed from Bacteroidetes, Deinococcus-Thermus, and Acidobacteria. Among reported genera, Achromobacter, Burkholderia, Bacillus, Enterobacter, Herbaspirillum, Pseudomonas, Pantoea, Rhizobium, and Streptomyces were dominant in most host plants. The present review deals with plant endophytic diversity, mechanisms of plant growth promotion, protection, and their role for agro-environmental sustainability. In the future, application of endophytic microbes have potential role in enhancement of crop productivity and maintaining the soil health in sustainable manner.

Genomic Analysis of a Novel Heavy Metal Resistant Isolate from a Black Sea Contaminated Sediment with the Potential to Degrade Alkanes: Plantactinospora alkalitolerans sp. nov

Microorganisms that grow in poorly studied environments are of special interest when new biotechnological applications are searched. The Melet river offshore sediments at the Black Sea have been described to contain an important number of contaminants from upstream industries which have been accumulating for years. Bacteria of such habitats must be adapted to the presence of those compounds and in some cases, are able to use them as carbon sources. In the analysis of some samples recovered from this environment, an actinobacterial strain was isolated, named as S1510T, and its taxonomic position was determined using a combination of phenotypic and genotypic properties. Strain S1510T presented phenotypic properties typical of members of the family Micromonosporaceae and was assigned to the Plantactinospora genus, based on the phylogenetic analyses of the 16S rRNA gene and whole-genome sequences. Low dDDH (digital DNA-DNA hybridization) values with other members of the genus confirmed that Plantactinospora sp. S1510T represents a novel species, and is proposed with the new name Plantactinospora alkalitolerans. The strain presented characteristics not previously described for other species in the genus, such as its high tolerance to alkaline pHs, the presence of genes related to the production and degradation of alkanes (oleABCD, ssuAD, almA), the degradation of several aromatic compounds, and the tolerance to high heavy metal concentrations. In addition, Plantactinospora sp. S1510T presents several bioclusters to produce nonribosomal peptide-synthetases, terpenes, polyketide synthases, and bacteriocins, that possess low similarities with known compounds.

Endophytic microbes: biodiversity, plant growth-promoting mechanisms and potential applications for agricultural sustainability

Endophytic microbes are known to live asymptomatically inside their host throughout different stages of their life cycle and play crucial roles in the growth, development, fitness, and diversification of plants. The plant-endophyte association ranges from mutualism to pathogenicity. These microbes help the host to combat a diverse array of biotic and abiotic stressful conditions. Endophytic microbes play a major role in the growth promotion of their host by solubilizing of macronutrients such as phosphorous, potassium, and zinc; fixing of atmospheric nitrogen, synthesizing of phytohormones, siderophores, hydrogen cyanide, ammonia, and act as a biocontrol agent against wide array of phytopathogens. Endophytic microbes are beneficial to plants by directly promoting their growth or indirectly by inhibiting the growth of phytopathogens. Over a long period of co-evolution, endophytic microbes have attained the mechanism of synthesis of various hydrolytic enzymes such as pectinase, xylanases, cellulase, and proteinase which help in the penetration of endophytic microbes into tissues of plants. The effective usage of endophytic microbes in the form of bioinoculants reduce the usage of chemical fertilizers. Endophytic microbes belong to different phyla such as Actinobacteria, Acidobacteria, Bacteroidetes, Deinococcus-thermus, Firmicutes, Proteobacteria, and Verrucomicrobia. The most predominant and studied endophytic bacteria belonged to Proteobacteria followed by Firmicutes and then by Actinobacteria. The most dominant among reported genera in most of the leguminous and non-leguminous plants are Bacillus, Pseudomonas, Fusarium, Burkholderia, Rhizobium, and Klebsiella. In future, endophytic microbes have a wide range of potential for maintaining health of plant as well as environmental conditions for agricultural sustainability. The present review is focused on endophytic microbes, their diversity in leguminous as well as non-leguminous crops, biotechnological applications, and ability to promote the growth of plant for agro-environmental sustainability.

Rhizobium glycinendophyticum sp. nov., isolated from roots of Glycine max (Linn. Merr.)

A Gram-stain-negative, rod-shaped and aerobic bacterium, designated CL12T, was isolated from roots of Glycine max (Linn. Merr.) collected from an experimental field in the campus of South China Agricultural University, PR China (22°58'46″S, 110°51'10″E). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CL12T belongs to the genus Rhizobium, closely related to Rhizobium wuzhouense W44T (99.3%), followed by Rhizobium rosettiformans W3T (98.0%) and Rhizobium ipomoeae Shin9-1T (97.9%). The results of analysis of sequences of four housekeeping genes (recA, atpD, rpoB and glnA) also revealed strain CL12T to be closely related to R. wuzhouense W44T with the similarities 91.0%, 95.0%, 94.2% and 90.5%, respectively. The major fatty acid of strain CL12T was Summed Feature 8 (C18:1ω7c and/or C18:1ω6c). Strain CL12T had not the nodulation genes (nodC and nodA) and nitrogenase reductase gene (nifH), and could not cause formation of nodule on soybean. The draft genome size of strain CL12T was 4.84 Mbp with a genomic DNA G + C content of 61.1 mol%. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) of strain CL12T and R. wuzhouense W44T were 27.4% and 84.7%, respectively. Based on genomic, phenotypic and phylogenetic analysis, strain CL12T is suggested to represent a new species of the genus Rhizobium, for which the name Rhizobium glycinendophyticum sp. nov. is proposed. The type strain is CL12T (=GDMCC 1.1597T = KACC 21281T).

Draft Genome Sequence of Two Marine Plantactinospora spp. from the Gulf of California

Plantactinospora sp. strains BB1 and BC1 were isolated in 2009 from sediment samples of the Gulf of California from among almost 300 actinobacteria. Genome mining of their ∼8.5-Mb sequences showed the bioprospecting potential of these rare actinomycetes, providing an insight to their ecological and biotechnological importance.