**4. Conclusions**

The gene-specific oligonucleotides corresponding to the coding DNA sequences for the enzymes responsible for the vital bacterial cell functions, such as EEP-like and DNA/RNA nonspecific nucleases, alkaline phosphatases PhoA and PhoD, proteases Cpl and Do/DeqQ family, and phospholipase A1, may be used for rapid molecular differentiation of the closely related species of the marine bacteria *Cobetia* in addition to the traditional 16S rRNA assay. Furthermore, the highly active alkaline phosphatase CmAP of the structural family PhoA is a highly specific marker for the species *C. amphilecti*, probably indicating the adaptability to the host–microbe relationships. However, the genus needs further study, including verification of the suggested molecular markers with the use of a higher number of isolates to develop the MLST-based method of identification. Primarily, comparative genomics of the type strains of *Cobetia* should be carried out to a final decision about the valid interspecies phylogeny of the genus, particularly towards the closely related species (*C. amphilecti* and *C. litoralis*; *C. marina* and *C. pacifica*), as well as about their genetic drivers and causes of such divergent evolution within the genus.

**Supplementary Materials:** The following are available online, Table S1: Similarity calculation of 16S rRNA gene sequences of *Cobetia* isolates by EzBioCloud 16S database, Table S2: Similarity calculation of 16S RNA gene sequence of the type strain *Cobetia marina* LMG 2217T, Table S3: Similarity calculation of 16S RNA gene sequence of the strain *Cobetia amphilecti* KMM 296, Table S4: Comparative analysis of coding DNA sequences of *Cobetia* sp. 2AS1 (KMM 7005) and *C. amphilecti* KMM 296.

**Author Contributions:** Conceptualization, L.B.; methodology, L.B. and O.N.; software, L.B.; validation, L.B. and O.N.; investigation, Y.N., A.S. and L.S.; resources, L.T., O.N., L.S.; data curation, L.B.; writing—original draft preparation, Y.N., A.S. and O.N.; writing—review and editing, L.B.; visualization, Y.N., A.S.; supervision, O.S.; project administration, O.S.; funding acquisition, L.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the isolates and DNA are available from the authors.
