Streptomyces meridianus sp. nov. isolated from brackish water of the Tagus estuary in Alcochete, Portugal

Abstract

An isolation effort focused on sporogenous Actinomycetota from the Tagus estuary in Alcochete, Portugal, yielded a novel actinomycetal strain, designated MTZ3.1^T, which was subjected to a polyphasic taxonomic study. MTZ3.1^T is characterised by morphology typical of members of the genus Streptomyces, with light beige coloured substrate mycelium, which does not release pigments to the culture medium and with helicoidal aerial hyphae that differentiate into spores with a light-grey colour. The phylogeny of MTZ3.1^T, based on the full 16S rRNA gene sequence, indicated that its closest relatives were Streptomyces alkaliterrae OF1^T (98.48 %), Streptomyces chumphonensis KK1-2^T (98.41 %), Streptomyces albofaciens JCM 4342^T (98.34 %), Streoptomyces paromomycinus NBRC 15454^T (98.34 %) and Streptomyces chrestomyceticus NRBC 13444^T (98.34 %). Moreover, average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA-DNA hybridisation (dDDH) are below the species cutoff values (ANI 67.70 and 68.35 %, AAI 77.06 and 76.71 % and dDDH 22.10 and 21.50 % for S. alkaliterrae OF1^T and S. chumphonensis KK1-2^T, respectively). Whole genome sequencing revealed that MTZ3.1^T has a genome of 5 644 485 bp with a DNA G+C content of 71.29 mol% and 5044 coding sequences. Physiologically, MTZ3.1^T is strictly aerobic, able to grow at 15-37 °C, optimally at 25 °C and between pH5 and 8 and showed high salinity tolerance, growing with 0-10 %(w/v) NaCl. Major cellular fatty acids are C_{15 : 0}, iso-C_{15 : 0}, anteiso-C_{15 : 0} and iso-C_{16 : 0}. Furthermore, it was able to utilise a variety of nitrogen and carbon sources. Antimicrobial screening indicated that MTZ3.1^T has potent anti-Staphylococcus aureus activity. On the basis of the polyphasic data, MTZ3.1^T is proposed to represent a novel species, Streptomyces meridianus sp. nov. (= CECT 30416^T = DSM 114037^T=LMG 32463^T).

Keywords: Actinomycetota; Streptomyces; Tagus river estuary; brackish water; novel taxa.