1-Aminociclopropane-1-carboxylate (ACC)-degrading bacteria having been widely studied for their use in alleviating abiotic stresses in plants. In the present study, we isolated and characterized ACC-degrading bacteria from the rhizosphere, phyllosphere, and endosphere of the Antarctic vascular plants Deschampsia antarctica and Colobanthus quitensis. One hundred and eighty of the 578 isolates (31%) were able to grow on minimal medium containing ACC, with 101 isolates (23, 37, and 41 endosphere-, phyllosphere- and rhizosphere-associated isolates, respectively) identified as being genetically unique by enterobacterial repetitive intergenic consensus (ERIC)-PCR. Subsequently, freeze/thaw treatments and ice-recrystallization-inhibition (IRI) activity assays were performed, the results of which revealed that 77 (13%) of cold-tolerant isolates exhibited putative ACC deaminase activity. Significant (p ≤ 0.05) differences in IRI activity were also observed between the studied plant niches. Surprisingly, all the cold-tolerant isolates showed ACC deaminase activity, independent of the plant niches, with 12 isolates showing the highest ACC deaminase activities of 13.21–39.56 mmol α KB mg protein⁻¹ h⁻¹. These isolates were categorized as ‘cold-tolerant hyper-ACC-degrading bacteria’, and identified as members of Pseudomonas, Serratia, and Staphylococcus genera. The results revealed the occurrence of cold-tolerant hyper-ACC-degrading bacteria in diverse plant niches of Antarctic vascular plants, that could be investigated as novel microbial inoculants to alleviate abiotic stresses in plants.

Microbiota associated with bivalves have drawn considerable attention because studies have suggested their relevance to the fitness and growth of marine bivalves. Although the mussel Choromytilus chorus is a valuable resource for Chilean aquaculture and fisheries, its microbiota is still unknown. In this study, the composition and predicted functions of the bacterial community in tissues of C. chorus specimens grown in an estuary (Nehuentue) and a bay (Hueihue) were investigated. Using 16S rRNA genes as targets, the bacterial abundance in tissues was estimated by quantitative PCR and sequenced via Illumina MiSeq. The abundances of bacteria ranged from 10³ to 10⁵ copies of 16S rRNA genes g⁻¹ tissue. In the Nehuentue estuary, the bacterial communities in the tissues were dominated by the Tenericutes phylum, whereas the Tenericutes and Proteobacteria phyla dominated in mussels from Hueihue Bay. Higher numbers of operational taxonomic units (OTUs) were observed in tissues from the Nehuentue Estuary than in those from Hueihue Bay. Differences in bacterial community compositions in tissues between both locations were confirmed by nonmetric multidimensional scaling (nMDS) and Venn diagram analysis. In addition, linear discriminant analysis effect size (LEfSe) revealed that the Mollicutes class and Actynomycetales order were key phylotypes in tissues from the Nehuentue Estuary and Hueihue Bay, respectively. Our analysis also predicted a high abundance of sequences assigned to heterotrophy; however, relatively high functional diversity was also found in tissues from Hueihue Bay. This work represents our first attempt to elucidate the C. chorus microbiota in contrasting Chilean aquatic environments.