Two Antarctic endophytic bacteria of <i>Colobanthus quitensis</i> show functional and genomic characteristics potentially responsible for plant growth promotion and cold tolerance

Bacterial endophytes reside in plant tissues and can promote plant growth under abiotic stresses. Complex microbial communities are associated with cold-adapted plants, but scarce information is available on the functional properties of Antarctic bacterial endophytes. This study aimed to investigate possible cold tolerance and plant growth promotion activities of two Antarctic bacterial endophytes by in vitro functional characterization and genome sequence analysis. Ewingella sp., Pseudomonas sp, and their bacterial consortium were cold tolerant and showed plant growth-promoting activity on tomato seedlings at low temperature. Phytohormones (indole-3-acetic acid) and proteases were produced by Ewingella sp. and Pseudomonas sp., respectively, while ammonia and siderophores were produced by both bacterial isolates and their consortium. Ewingella sp. and Pseudomonas sp. genomes encompassed genes possibly involved in plant growth promotion (e.g., auxin, cytokinin, ethylene, salicylic acid, and siderophore metabolism and transport) and genes related to bacterial metabolic processes that can contribute to plant growth-promoting activities, such as amino acid metabolism, iron transport, nitrogen metabolism, and lytic activities (amylases, cellulases, and proteases), phosphate metabolism, potassium transport, and zinc transport. Moreover, Ewingella sp. and Pseudomonas sp. encompassed genes possibly associated with bacterial cold tolerance that can contribute to cold stress mitigation in the plant host, such as cold shock- and heat shock-related proteins, lipid desaturases, polyamine metabolism, proline metabolism, proline and glycine betaine transport, reactive oxygen species detoxification, and trehalose metabolism. Antarctic bacterial endophytes include multiple characteristics to survive under cold conditions and some bacterial functions can contribute to plant growth promotion and stress mitigation at low temperature.