Results

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The genome sizes of the Tellurirhabdus and Larkinella species ranged from 4941522 to 8175905 bp, with G+C content ranging from 48.8 to 57.6%. The number of tRNAs ranged from 39 to 50. The genome was >90% complete, with <5% contamination. Detailed genome traits of Tellurirhabdus and Larkinella species are mentioned in Table 1. In the present study, the ANI values (Table 2) among Larkinella, Tellurirhabdus, and Dyadobacter species were below 95-96%. In the phylogenomic tree, Larkinella and Tellurirhabdus species showed a distinct clade (Figure. 1). A similar clade was noticed when the trees were constructed using NJ, ML, and MP methods (Figure S1, S2, and S3). In the present study, the AAI values among Larkinella and Tellurirhabdus were evaluated. Based on the data in Table 3, the AAI value between Tellurirhabdus rosea U15T and the analyzed Larkinella species ranged from 68.7% to 70.1%, while the value between Tellurirhabdus bombi IE-0392T and the Larkinella species ranged from 70.8% to 71.3%.

The genera Larkinella and Tellurirhabdus are the members of the family Spirosomataceae [3]. Both genera are Gram-negative and aerobic [1, 2]. Recently Zhang et al., reported that Tellurirhabdus species share phenotypic and chemotaxonomic characteristics similar to Larkinella species [10]. The present study reviewed the taxonomic status of the taxa Larkinella and Tellurirhabdus. The genomes were downloaded and their quality assessed using CheckM, as it offers methods for assessing genome quality and providing reliable estimates of completeness and contamination by utilizing ubiquitous, single-copy genes within a phylogenetic lineage [19]. Good-quality genomes exhibit completeness levels more than 90% and contamination levels less than 5% [19]. The Larkinella and Tellurirhabdus genomes downloaded from NCBI have high completeness and low contamination levels (>90 and <5%, respectively), indicating high quality genomes [19]. 

The ANI value was introduced for species-level delineation and a cut-off value of 95-96% was proposed [27]. In the present study, the ANI values among Larkinella, Tellurirhabdus, and Dyadobacter species were below 95-96% indicating they were different species [27]. Similarly, AAI was introduced to delineate strains at the genus level by measuring the average amino acid identity of all shared genes between two strains, allowing for an assessment of their genetic relatedness [28] and the threshold value of >60–65 % was also proposed [28, 29]. The AAI values between Larkinella and Tellurirhabdus were above the threshold value of genus delineation (>60–65 %) indicating that they were members of the same genus. Since the genus Larkinella was published earlier than Tellurirhabdus [1, 2] hence Tellurirhabdus species should be transferred to the genus Larkinella. We propose transferring Tellurirhabdus bombi as Larkinella bombi comb. nov. Since Tellurirhabdus rosea would be a later homonym of Larkinella rosea, a name already assigned to a species in the genus Larkinella, the name Larkinella roseola nom. nov. is proposed. In addition, the culture deposition certificates of Tellurirhabdus species are depicted in Figure S4.

The taxonomic position of the genera Larkinella and Tellurirhabdus was evaluated using genome analysis. The genome size of Larkinella and Tellurirhabdus species ranged from 4941522-8175905 bp and their G+C content ranged from 48.8-57.6%. The number of tRNAs ranged from 39-50. CheckM analysis revealed that Larkinella and Tellurirhabdus species genome completeness and contamination were >90 and <5%, respectively indicating good-quality genomes. The ANI values among Larkinella and Tellurirhabdus species were below the cut-off for species delineation indicating they were different species. However, the AAI values were above the cut-off value (>60–65 %) for genus delineation indicating they belong to the same genus. Based on the above results, we propose to transfer Tellurirhabdus rosea to the genus Larkinella as Larkinella roseola nom. nov., and Tellurirhabdus bombi as Larkinella bombi comb. nov.

Larkinella roseola (ro.se'o.la. N.L. fem. adj. roseola, rose-colored, pink).

Basonym: Tellurirhabdus rosea Choi et al.

The description of this species is the same as provided by Choi et al., [2] for Tellurirhabdus rosea. The type strain is U15^T (= KCTC 62116^T = JCM 32361^T). Larkinella bombi (bom’bi. L. n. bombus a boom, a deep hollow noise, buzzing, also the zoological genus name of the bumblebee; N.L. gen. n. bombi of Bombus, of a bumblebee).

Basonym: Tellurirhabdus bombi Zhang et al.

The description of this species is the same as provided by Zhang et al., [10] for Tellurirhabdus bombi. The type strain is IE-0392^T (= GDMCC 1.2794^T = JCM 35040^T).

Tables and Figures