Trinickia dabaoshanensis sp. nov., a new name for a lost species

Trinickia violacea sp. nov. and Trinickia terrae sp. nov., isolated from forest soil

Two Gram-stain negative, aerobic and rod-shaped bacterial strains, DHOD12T and 7GSK02T, were isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China. Strain DHOD12T grew at 4-42 °C (optimum, 28-33 °C), pH 4.0-8.5 (optimum, pH 5.5-6.5) and in the presence of 0-1.5 % (w/v; optimum, 0-0.5 %)NaCl; while strain 7GSK02T grew at 12-42 °C (optimum, 28-33 °C), pH 4.0-8.5 (optimum, pH 5.0-6.0) and in the presence of 0-0.5 % (w/v; optimum, 0 %) NaCl. Strains DHOD12T and 7GSK02T had the highest 16S rRNA sequence similarities of 98.0 and 98.3 % with the same species Trinickia mobilis DHG64T, respectively, and 98.4 % between themselves. In the 16S rRNA phylogeny, they formed a clade that was sister to a major cluster consisting of all described Trinickia species. Phylogenomic analyses with the UBCG and PhyloPhlAn methods consistently showed that strains DHOD12T and 7GSK02T formed a clade with T. mobilis DHG64T that was a sister of a cluster containing the remainder of the Trinickia species. The DNA G+C contents of strains DHOD12T and 7GSK02T were 63.1 and 64.6 mol%, respectively. Digital DNA-DNA hybridization and average nucleotide identity values of strains DHOD12T, 7GSK02T and their closely related strains were in the ranges of 21.6-31.4 % and 77.1-86.9 %, respectively. These two strains had the same major respiratory quinone, ubiquinone-8, and both had C16 : 0, C17 : 0 cyclo and summed feature 8 (C18 : 1  ω7c/C18 : 1  ω6c) as their major fatty acids. Their major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. Genomic analysis indicated that the two strains could have the potential to degrade aromatic compounds like other Trinickia species. On the basis of phenotypic and phylogenetic results, strains DHOD12T and 7GSK02T represent two novel species of the genus Trinickia, for which the names Trinickia violacea sp. nov. (type strain DHOD12T=LMG 30258T=CGMCC 1.15436T) and Trinickia terrae sp. nov. (type strain 7GSK02T=CGMCC 1.15432T=KCTC 62468T) are proposed.

Burkholderia orbicola sp. nov., a novel species within the Burkholderia cepacia complex

Genome analysis of strains placed in the NCBI genome database as Burkholderia cenocepacia defined nine genomic species groups. The largest group (259 strains) corresponds to B. cenocepacia and the second largest group (58 strains) was identified as "Burkholderia servocepacia", a Burkholderia species classification which has not been validly published. The publication of "B. servocepacia" did not comply with Rule 27 and Recommendation 30 from the International Code of Nomenclature of Prokaryotes (ICNP) and have errors in the type strain name and the protologue describing the novel species. Here, we correct the position of this species by showing essential information that meets the criteria defined by ICNP. After additional analysis complying with taxonomic criteria, we propose that the invalid "B. servocepacia" be renamed as Burkholderia orbicola sp. nov. The original study proposing "B. servocepacia" was misleading, because this name derives from the Latin "servo" meaning "to protect/watch over", and the authors proposed this based on the beneficial biocontrol properties of several strains within the group. However, it is clear that "B. servocepacia" isolates are capable of opportunistic infection, and the proposed name Burkholderia orbicola sp. nov. takes into account these diverse phenotypic traits. The type strain is TAtl-371 ^T (= LMG 30279 ^T = CM-CNRG 715 ^T).

The Hidden Genomic Diversity, Specialized Metabolite Capacity, and Revised Taxonomy of Burkholderia Sensu Lato

Burkholderia sensu lato is a collection of closely related genera within the family Burkholderiaceae that includes species of environmental, industrial, biotechnological, and clinical importance. Multiple species within the complex are the source of diverse specialized metabolites, many of which have been identified through genome mining of their biosynthetic gene clusters (BGCs). However, the full, true genomic diversity of these species and genera, and their biosynthetic capacity have not been investigated. This study sought to cluster and classify over 4000 Burkholderia sensu lato genome assemblies into distinct genomic taxa representing named and uncharacterized species. We delineated 235 species groups by average nucleotide identity analyses that formed seven distinct phylogenomic clades, representing the genera of Burkholderia sensu lato: Burkholderia, Paraburkholderia, Trinickia, Caballeronia, Mycetohabitans, Robbsia, and Pararobbisa. A total of 137 genomic taxa aligned with named species possessing a sequenced type strain, while 93 uncharacterized species groups were demarcated. The 95% ANI threshold proved capable of delineating most genomic species and was only increased to resolve several closely related species. These analyses enabled the assessment of species classifications of over 4000 genomes, and the correction of over 400 genome taxonomic assignments in public databases into existing and uncharacterized genomic species groups. These species groups were genome mined for BGCs, their specialized metabolite capacity calculated per species and genus, and the number of distinct BGCs per species estimated through kmer-based de-replication. Mycetohabitans species dedicated a larger proportion of their relatively small genomes to specialized metabolite biosynthesis, while Burkholderia species harbored more BGCs on average per genome and possessed the most distinct BGCs per species compared to the remaining genera. Exploring the hidden genomic diversity of this important multi-genus complex contributes to our understanding of their taxonomy and evolutionary relationships, and supports future efforts toward natural product discovery.

'Candidatus Xiphinematincola pachtaicus' gen. nov., sp. nov., an endosymbiotic bacterium associated with nematode species of the genus Xiphinema (Nematoda, Longidoridae)

An intracellular bacterium, strain IAST, was observed to infect several species of the plant-parasitic nematode genus Xiphinema (Xiphinema astaregiense, Xiphinema incertum, Xiphinema madeirense, Xiphinema pachtaicum, Xiphinema parapachydermum and Xiphinema vallense). The bacterium could not be recovered on axenic medium. The 16S rRNA gene sequence of IAST was found to be new, being related to the family Burkholderiaceae, class Betaproteobacteria. Fungal endosymbionts Mycoavidus cysteinexigens B1-EBT (92.9 % sequence identity) and 'Candidatus Glomeribacter gigasporarum' BEG34 (89.8 % identity) are the closest taxa and form a separate phylogenetic clade inside Burkholderiaceae. Other genes (atpD, lepA and recA) also separated this species from its closest relatives using a multilocus sequence analysis approach. These genes were obtained using a partial genome of this bacterium. The localization of the bacterium (via light and fluorescence in situ hybridization microscopy) is in the X. pachtaicum females clustered around the developing oocytes, primarily found embedded inside the epithelial wall cells of the ovaries, from where they are dispersed in the intestine. Transmission electron microscopy (TEM) observations supported the presence of bacteria inside the nematode body, where they occupy ovaries and occur inside the intestinal epithelium. Ultrastructural analysis of the bacterium showed cells that appear as mostly irregular, slightly curved rods with rounded ends, 0.8-1.2 µm wide and 2.5-6.0 µm long, possessing a typical Gram-negative cell wall. The peptidoglycan layer is, however, evident only occasionally and not detectable by TEM in most cells. Another irregularly occurring shell surrounding the endosymbiont cells or the cell clusters was also revealed, probably originating from the host cell membrane. Flagella or spore-like cells do not occur and the nucleoid is diffusely distributed throughout the cell. This endosymbiont is transmitted vertically through nematode generations. These results support the proposal of IAST as a new species, although its obligate intracellular and obligate endosymbiont nature prevented isolation of a definitive type strain. Strain IAST is therefore proposed as representing 'Candidatus Xiphinematincola pachtaicus' gen. nov., sp. nov.

Bradyrhizobium sp. sv. retamae nodulates Retama monosperma grown in a lead and zinc mine tailings in Eastern Morocco

The aim of this work was to characterize and identify some bacteria isolated from the root nodules of Retama monosperma grown in Sidi Boubker lead and zinc mine tailings. Very few root nodules were obtained on the root nodules of R. monosperma grown in these soils. The three bacteria isolated from the root nodules were tolerant in vitro to different concentrations of heavy metals, including lead and zinc. The rep-PCR experiments showed that the three isolates have different molecular fingerprints and were considered as three different strains. The analysis of their 16S rRNA gene sequences proved their affiliation to the genus Bradyrhizobium. The analysis and phylogeny of the housekeeping genes atpD, glnII, gyrB, recA, and rpoB confirmed that the closest species was B. valentinum with similarity percentages of 95.61 to 95.82%. The three isolates recovered from the root nodules were slow-growing rhizobia capable to renodulate their original host plant in the presence of Pb-acetate. They were able to nodulate R. sphaerocarpa and Lupinus luteus also but not Glycine max or Phaseolus vulgaris. The phylogeny of the nodA and nodC nodulation genes as well as the nifH gene of the three strains showed that they belong to the symbiovar retamae of the genus Bradyrhizobium. The three strains isolated could be considered for use as inoculum for Retama plants before use in phytoremediation experiments.

Characterization of Pisum sativum and Vicia faba microsymbionts in Morocco and definition of symbiovar viciae in Rhizobium acidisoli

In this work, we analyzed the diversity of seventy-six bacteria isolated from Pea and faba bean nodules in two regions of Morocco. The molecular diversity was realized using the analysis of the sequences of 16S rRNA and six housekeeping genes (recA, glnII, atpD, dnaK, rpoB and gyrB) and two symbiotic genes (nodA and nodC). The phylogeny of the 16S rRNA gene sequences revealed that all strains belong to the genus Rhizobium, being related to the type strains of R. leguminosarum, R. laguerreae, R. indigoferae, R. anhuiense and R. acidisoli. The housekeeping genes phylogenies showed that some strains formed a subclade distinct from the rhizobial species that usually nodulate Vicia faba and Pisum sativum which are closely related to R. acidisoli FH23 with sequence similarity of 98.3%. Analysis of the PGPR activities of the different isolates showed that the strains related to R. laguerreae were able to solubilize phosphates and to produce siderophores and auxin phytohormone. However, R. acidisoli strain F40D2 was unable to solubilize phosphates although they produce siderophores and IAA. The phylogenetic analysis of the nodA and nodC sequences showed that all isolated strains were closely related with the strains of symbiovar viciae. The nodulation tests confirmed the ability to nodulate V. faba and P. sativum but not Cicer arietinum or Phaseolus vulgaris. Hence, in Morocco P. sativum is nodulated by R. laguerreae; whereas V. faba is nodulated by R. laguerreae and the symbiovar viciae of R. acidisoli which has been not previously described in this species.

Deciphering the Symbiotic Plant Microbiome: Translating the Most Recent Discoveries on Rhizobia for the Improvement of Agricultural Practices in Metal-Contaminated and High Saline Lands

Rhizosphere and plant-associated microorganisms have been intensely studied for their beneficial effects on plant growth and health. These mainly include nitrogen-fixing bacteria (NFB) and plant-growth promoting rhizobacteria (PGPR). This beneficial fraction is involved in major functions such as plant nutrition and plant resistance to biotic and abiotic stresses, which include water deficiency and heavy-metal contamination. Consequently, crop yield emerges as the net result of the interactions between the plant genome and its associated microbiome. Here, we provide a review covering recent studies on PGP rhizobia as effective inoculants for agricultural practices in harsh soil, and we propose models for inoculant combinations and genomic manipulation strategies to improve crop yield.