Amycolatopsis echigonensis sp. nov. and Amycolatopsis niigatensis sp. nov., novel actinomycetes isolated from a filtration substrate

New insights into the relationship between the average nucleotide identity and the digital DNA-DNA hybridization values in the genus Amycolatopsis and Amycolatopsis cynarae sp. nov., a novel actinobacterium from the rhizosphere soil of Cynara scolymus, and proposal of Amycolatopsis niigatensis as a synonym of Amycolatopsis echigonensis based on comparative genomic analysis

At present, it is widely believed that a 95-96% average nucleotide identity (ANI) value is equivalent to a 70% digital DNA-DNA hybridization (dDDH) value in the prokaryotic taxonomy. However, in the present study, comparative genome analysis of 29 pairs of Amycolatopsis type strains revealed that a 70% dDDH value did not correspond to a 95-96% ANI based on the MuMmer ultra-rapid aligning tool (ANIm) but approximately corresponded to a 96.6% ANIm value in the genus Amycolatopsis. Based on this corresponding relationship, phenotypic and chemotaxonomical characteristics, as well as phylogenetic analysis, an actinobacterial strain HUAS 11-8T isolated from the rhizosphere soil of Cynara scolymus, was subjected to a polyphasic taxonomic characterization. Based on EzBioCloud alignment, it was found that strain HUAS11-8T had the 16S rRNA gene similarities of 99.78% with A. rhizosphaerae JCM 32589T, 97.8% with A. dongchuanensis YIM 75904T, and < 97.8% sequence similarities to other Amycolatopsis species. Phylogenetic analysis of 16S rRNA gene sequences and whole-genome sequences revealed that strain HUAS 11-8T was closely related to A. rhizosphaerae JCM 32589T. ANIm and dDDH values between strains HUAS 11-8T and A. rhizosphaerae JCM 32589T were 96.3 and 68.5%, respectively, lower than the 96.6 and 70% thresholds recommended for the delineation of a novel Amycolatopsis species. Consequently, strain HUAS 11-8T should represent a novel Amycolatopsis species, for which the name Amycolatopsis cynarae sp. nov. (type strain HUAS 11-8T = MCCC 1K08337T = JCM 35980T) is proposed. Furthermore, based on comparative genomic analysis and rule 42 of the Prokaryotic Code, we propose that Amycolatopsis niigatensis is a later heterotypic synonym of Amycolatopsis echigonensis.

Genome-Based Taxonomic Classification of the Phylum Actinobacteria

The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

Amycolatopsis stemonae sp. nov., isolated from a Thai medicinal plant

A novel actinomycete, strain ST1-08T, was isolated from the stem of Stemona sp. in Thailand. The taxonomic position of this isolate was determined by using a polyphasic approach. Strain ST1-08T contained meso-diaminopimelic acid in the cell-wall peptidoglycan, and arabinose and galactose as diagnostic sugars of the whole-cell hydrolysate, which are typical properties of members of the genus Amycolatopsis. Strain ST1-08T grew at 15-40 °C, pH 6-9 and on 5 % (w/v) NaCl. Gelatin liquefaction, starch hydrolysis and skimmed milk peptonization were positive. The strain utilized l-arabinose, d-glucose, glycerol, myo-inositol, d-mannitol and l-rhamnose. The predominant menaquinone was MK-9(H4) and the major cellular fatty acids were iso-C16 : 0 and iso-C15 : 0.The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, hydroxyl-phosphatidylethanolamine, phosphatidylinositol and phosphatidylglycerol. The 16S rRNA gene sequence analysis revealed that the strain was closely related to Amycolatopsis pretoriensis JCM 12673T (98.99 %) and Amycolatopsis lexingtonensis JCM 12672T (98.87 %). The DNA G+C content of strain ST1-08T was 71.2 mol%. The DNA-DNA relatedness values among strain ST1-08T, A. pretoriensis JCM 12673T and A. lexingtonensis JCM 12672T were lower than 70 %, the cut-off level for assigning strains to the same species. On the basis of phenotypic and genotypic characteristics, strain ST1-08T represents a novel species of the genus Amycolatopsis, for which the name Amycolatopsis stemonae is proposed. The type strain is ST1-08T( = JCM 30050T = PCU 339T = TISTR 2278T).

Arthrobacter liuii sp. nov., resuscitated from Xinjiang desert soil

A Gram-stain positive, aerobic, non-motile actinobacterium, designated DSXY973(T), was isolated from soil samples collected from Xinjiang desert using medium supplemented with resuscitation-promoting factor, and subjected to a polyphasic taxonomic investigation. Phylogenetic analysis based on 16S rRNA gene sequences revealed that DSXY973(T) belonged to the genus Arthrobacter and was most closely related to Arthrobacter oryzae JCM 15922(T) with 97.1 % similarity. The DNA G+C content was 67.6 %. Cells of strain DSXY973(T) mainly contained MK-9(H2), and the cell wall contained l-lysine as the primary diamino acid. The major cellular fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C15 : 0. Strain DSXY973(T) was positive for catalase and negative for oxidase activity. On the basis of its phylogenetic position and phenotypic properties, strain DSXY973(T) represents a novel species of the genus Arthrobacter, for which the name Arthrobacter liuii sp. nov. is proposed. The type strain is DSXY973(T) ( = CGMCC1.12778(T) = JCM 19864(T)).

Exploring the potential environmental functions of viable but non-culturable bacteria

A conventional plate count is the most commonly employed method to estimate the number of living bacteria in environmental samples. In fact, judging the level of viable culture by plate count is limited, because it is often several orders of magnitude less than the number of living bacteria actually present. Most of the bacteria are in "viable but non-culturable" (VBNC) state, whose cells are intact and alive and can resuscitate when surrounding conditions are more favorable. The most exciting recent development in resuscitating VBNC bacteria is a bacterial cytokine, namely, the resuscitation-promoting factor (Rpf), secreted by Micrococcus luteus, which promotes the resuscitation and growth of high G+C Gram-positive organisms, including some species of the genus Mycobacterium. However, most of studies deal with VBNC bacteria only from the point of view of medicine and epidemiology. It is therefore of great significance to research whether these VBNC state bacteria also possess some useful environmental capabilities, such as degradation, flocculation, etc. Further studies are needed to elucidate the possible environmental role of the VBNC bacteria, rather than only considering their role as potential pathogens from the point view of epidemiology and public health. We have studied the resuscitation of these VBNC bacteria in polluted environments by adding culture supernatant containing Rpf from M. luteus, and it was found that, as a huge microbial resource, VBNC bacteria could provide important answers to dealing with existing problems of environmental pollution. This mini-review will provide new insight for considering the potentially environmental functions of VBNC bacteria.

Evaluation of the use of recN sequence analysis in the phylogeny of the genus Amycolatopsis

Partial recN gene sequences (>1 kb) were obtained from 35 type strains of the genus Amycolatopsis. Phylogenetic trees were constructed to determine the effectiveness of using this gene to predict taxonomic relationships within the genus. The use of recN sequence analysis as an alternative to DNA-DNA hybridization (DDH) for distinguishing closely related species was also assessed. The recN based phylogeny mostly confirmed the conventional 16S rRNA and gyrB gene-based phylogenies and thus provides further support for these phylogenetic groupings. As is the case for the gyrB gene, pairwise recN sequence similarities cannot be used to predict the DNA relatedness between type strains but the recN genetic distance can be used as a means to assess quickly whether an isolate is likely to represent a new species in the genus Amycolatopsis. A recN genetic distance of >0.04 between two Amycolatopsis strains is proposed to provide a good indication that they belong to different species (and that polyphasic taxonomic characterization of the unknown strain is worth undertaking).

Evaluation of the antibiotic biosynthetic potential of the genus Amycolatopsis and description of Amycolatopsis circi sp. nov., Amycolatopsis equina sp. nov. and Amycolatopsis hippodromi sp. nov

AIMS

To describe three new Amycolatopsis strains and assess the antibiotic biosynthetic potential of the genus.

METHODS AND RESULTS

Three strains, designated S1·3(T) , S3·6(T) and SE(8)3(T) , belonging to the genus Amycolatopsis were isolated and found to cluster together by 16S rRNA and gyrB gene-based phylogenetic analysis. Genetic distance values, based on the gyrB gene, were calculated between the strains and their closest relatives and were all above the threshold value of 0·02 that has been proposed to distinguish Amycolatopsis type strains. DNA-DNA hybridization experiments against related type strains confirmed that strain S3·6(T) represents a unique genomic species. Strain S3·6(T) was also found to be distinct from strains S1·3(T) and SE(8)3(T) , the latter two of which were also shown to be distinct from each other. Antibiotic biosynthetic genes were identified from multiple Amycolatopsis strains, and their presence was found to be phylogenetically associated.

CONCLUSIONS

The data presented in this study indicate that strains S1·3(T) , SE(8)3(T) and S3·6(T) belong to three novel species, for which the names Amycolatopsis circi sp. nov. (= DSM 45561(T) = NRRL B-24841(T) ), Amycolatopsis equina sp. nov. (= DSM 45563(T) = NRRL B-24842(T) ) and Amycolatopsis hippodromi sp. nov. (= DSM 45562(T) = NRRL B-24843(T) ) are proposed.

SIGNIFICANCE AND IMPACT OF THE STUDY

Three new species of Amycolatopsis are described, and the knowledge of the antibiotic biosynthetic potential of the genus has been extended.

Study on the flocculability of the Arthrobacter sp., an actinomycete resuscitated from the VBNC state

A bioflocculant with high flocculating activity, LC13-SF, produced by strain LC13(T) which was in a viable but nonculturable (VBNC) state, and which was woken up by Rpf (resuscitation promoting factor), was systematically investigated with regard to its fermentation conditions and flocculating activity. The key parameters influencing the bioflocculant LC13-SF were investigated through measuring the optical density at 660 (OD(660)) of the fermentation liquid and the optical density at 550 (OD(550)) of the centrifugal supernatant. The flocculating efficiency and the Zeta potentials were chosen as the response variables for the study of the flocculating activity. The results showed that the optimal conditions for bioflocculant LC13-SF production were a fermentation time of 72 h, an initial pH of 7.0, a fermentation temperature of 30°C and a shaking speed of 150 r/min. The optimized flocculating process was as follows: a final volume percentage of bioflocculant LC13-SF and 0.5% (w/w) CaCl(2) were 1.5 and 5%, respectively in a 4 g/L Kaolin suspension, and the system pH was adjusted to 8.0. Under these conditions, the flocculating efficiency and the absolute value of the Zeta potential reached 94.83% and 4.37, respectively.

Amycolatopsis halophila sp. nov., a halophilic actinomycete isolated from a salt lake

A novel halophilic actinomycete, designated strain YIM 93223(T), was isolated from a salt lake in Xinjiang Province, north-west China, and was subjected to a polyphasic taxonomic study. The isolate grew at 25-45 degrees C, at pH 6-8 and in the presence of 1-15 % (w/v) NaCl; no growth was observed in the absence of NaCl. Strain YIM 93223(T) contained meso-diaminopimelic acid, glutamic acid and alanine as cell-wall amino acids, and glucose and galactose as major whole-cell-wall sugars. Major fatty acids were iso-C(16 : 0), C(16 : 0) and C(16 : 1)omega7c/iso-C(15 : 0) 2-OH. MK-8(H(4)) was the predominant menaquinone. The genomic DNA G+C content was 66.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM 93223(T) belongs to the genus Amycolatopsis. It shared highest 16S rRNA gene sequence similarity with Amycolatopsis palatopharyngis 1BDZ(T) (96.6 %) and Amycolatopsis marina Ms392A(T) (96.4 %), but lower values (94.5-96.2 %) with the type strains of other recognized species of the genus Amycolatopsis. On the basis of the data from this polyphasic study, strain YIM 93223(T) is considered to represent a novel species of the genus Amycolatopsis, for which the name Amycolatopsis halophila sp. nov. is proposed. The type strain is YIM 93223(T) (=DSM 45216(T) =KCTC 19403(T)).