Unveiling the culturable and non‐culturable actinobacterial diversity in two macroalgae species from the northern Portuguese coast

Abstract

Actinomycetota, associated with macroalgae, remains one of the least explored marine niches. The secondary metabolism of Actinomycetota, the primary microbial source of compounds relevant to biotechnology, continues to drive research into the distribution, dynamics, and metabolome of these microorganisms. In this study, we employed a combination of traditional cultivation and metagenomic analysis to investigate the diversity of Actinomycetota in two native macroalgae species from the Portuguese coast. We obtained and taxonomically identified a collection of 380 strains, which were distributed across 12 orders, 15 families, and 25 genera affiliated with the Actinomycetia class, with Streptomyces making up approximately 60% of the composition. Metagenomic results revealed the presence of Actinomycetota in both Chondrus crispus and Codium tomentosum datasets, with relative abundances of 11% and 2%, respectively. This approach identified 12 orders, 16 families, and 17 genera affiliated with Actinomycetota, with minimal overlap with the cultivation results. Acidimicrobiales emerged as the dominant actinobacterial order in both macroalgae, although no strain affiliated with this taxonomic group was successfully isolated. Our findings suggest that macroalgae represent a hotspot for Actinomycetota. The synergistic use of both culture‐dependent and independent approaches proved beneficial, enabling the identification and recovery of not only abundant but also rare taxonomic members.

Cellulamides: A New Family of Marine-Sourced Linear Peptides from the Underexplored Cellulosimicrobium Genus

“…Strain CT-R177 was obtained from one specimen of the Chlorophyta Codium tomentosum , collected in January 2020 in the intertidal area of the northern Portuguese rocky shore (41.309298°; −8.742228°), as described in Girão et al, 2024 [ 27 ]. The macroalgae was processed in the laboratory for Actinomycetota isolation and, from its holdfast tissues, strain CT-R177 was isolated in Actinomycete Isolation Agar (AIA) [ 27 ]. After 48–72 h of incubation at 28 °C, this aerobic, non-sporulating strain exhibited colonies with a small-size rod-shaped morphology and a bright yellow coloration.…”

“…Strain CT-R177 was taxonomically identified through 16S rRNA gene sequencing, as described in Girão et al, 2024 [ 27 ]. To infer the evolutionary relationship between strain CT-R177 and their closest relatives, a phylogenetic tree using the maximum-likelihood (ML) method, based on the Tamura–Nei model, was constructed using the 16S rRNA gene sequences of the described type strains closest to strain CT-R177.…”

“…In this study, we have explored the secondary metabolism of Cellulosimicrobium funkei CT-R177, a strain isolated from the tissues the green macroalgae Codium tomentosum collected in the rocky intertidal northern Portuguese coast [ 27 ]. Based on the bioactive properties displayed by the extract of this strain, and the opportunity for exploring rare Actinomycetota taxa for the production of novel chemistry, our goal was to isolate and elucidate the structure of novel molecules detected in the CT-R177 metabolome, representing the first reported NPs from the rare Actinomycetota genus Cellulosimicrobium.…”