Draft:Algimonas arctica

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Algimonas arctica is a Gram-negative, aerobic, dimorphic bacterium isolated from intertidal sand in Kongsfjorden, Svalbard, within the Arctic Circle. It was proposed as a novel species within the genus Algimonas based on phylogenetic, genomic, and morphological analyses.

Algimonas arctica
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Alphaproteobacteria
Order:	Caulobacterales
Family:	Robiginitomaculaceae
Genus:	Algimonas
Species:	A. arctica
Binomial name
Algimonas arctica (Liu et al. 2015)
Type strain
SM1216ᵀ
Species
Algimonas porphyrae Algimonas ampicilliniresistens Algimonas arctica

Etymology

The genus name Algimonas is derived from the Latin alga, meaning “seaweed,” and the Greek monas (μονάς), meaning “a single unit” or “monad,” commonly used in bacterial nomenclature. This name reflects the genus' marine origin. The second part of the species name, arctica, refers to the Arctic region where the bacterium was first isolated, specifically from intertidal sand in Svalbard.

Taxonomy and Phylogenetic Description

Algimonas arctica is a Gram-negative bacterium classified within the domain Bacteria and the phylum Pseudomonadota (previously known as Proteobacteria). According to NCBI taxonomy classifications, it falls under the class Alphaproteobacteria, order Maricaulales, and family Robiginitomaculaceae. The genus Algimonas, to which it belongs, currently includes three known species: A. porphyrae, A. ampicilliniresistens, and A. arctica. In 2013, the genus Algimonas was first formally established following the identification of A. porphyrae. Early literature assigned Algimonas to the Hyphomonadaceae family, but recent taxonomic evaluation has reassigned the genus to Robiginitomaculaceae.

Phylogenetic comparisons have been made using 16S rRNA gene sequencing to accurately place Algimonas arctica within the genus Algimonas. This revealed phylogenetic relevance of this bacterium as it had 97.5% sequence identity similarity with A. ampicilliniresistens and 96.3% with A. porphyrae. Despite its similarity, DNA-DNA hybridization experiments comparing genetic similarity showed only 57.9% relatedness between A. arctica and its closest known relative A. ampicilliniresistens, confirming it as a distinct species. The bacterium forms a separate phylogenetic branch alongside other Algimonas species, differentiating it from members of the related genera Litorimonas, Hellea, and Robiginitomaculum.

Discovery

Algimonas arctica was first discovered in 2011 during the 8th Chinese National Arctic Yellow River Station Scientific Expedition. The bacterium was isolated from an Arctic intertidal sand sample collected at Kongsfjorden, Svalbard (78°55′2.8″N 11°58′14.4″E), a fjord system known for its unique combination of glacial inputs, seawater influence, and diverse microbial communities. This environment provided a cold, marine-influenced habitat ideal for discovering psychrotolerant and halotolerant microorganisms capable of surviving in extreme Arctic conditions.

Isolation

Approximately 10 grams of intertidal sand were suspended in sterile artificial seawater and serially diluted. The diluted suspension was plated on Trypticase soy agar—a nutrient medium containing tryptone, yeast extract, and sea salts—designed to mimic marine conditions while encouraging the growth of heterotrophic, salt-tolerant aerobic bacteria. Plates were incubated at 15°C for 2–4 weeks to select for cold-adapted microorganisms. Colonies were chosen based on distinct morphological characteristics, including pigmentation and shape, and were then purified through repeated streaking on fresh media.

This method selectively enriched for slow-growing, pigmented, marine-adapted bacteria with the metabolic flexibility to thrive under low-temperature, nutrient-variable conditions typical of Arctic sediment environments. One such isolate, designated strain SM1216^T, exhibited distinct phenotypic and genetic characteristics that led to its classification as a novel species.

Classification

Strain SM1216^T underwent 16S rRNA gene sequencing, revealing 97.5% and 96.3% similarity to Algimonas ampicilliniresistens and Algimonas porphyrae, respectively—its two closest relatives within the genus Algimonas. However, DNA–DNA hybridization values between SM1216^T and A. ampicilliniresistens were only 57.9%, well below the 70% threshold for species delineation. This, along with distinctive biochemical and morphological features, supported the classification of Algimonas arctica as a novel species. The type strain was deposited in two microbial culture collections under the identifiers MCCC 1K00233^T and KCTC 32513^T.

Morphology

Algimonas arctica is a Gram-negative, aerobic, dimorphic, rod-shaped bacterium within the family Hyphomonadaceae. Cells typically measure between 1–2 μm in length and 0.3–0.4 μm in width. A distinctive feature of this species, consistent with others in the genus Algimonas, is the presence of either a single polar prostheca or a single polar flagellum, which contributes to its dimorphic nature and motility.

Colonies of A. arctica grown on Trypticase soy agar at 20°C appear pale orange, round, smooth, and convex, with a diameter ranging from 0.5–2.0 mm after 5–7 days of incubation. The orange pigmentation is due to the production of carotenoid pigments, though the species does not produce bacteriochlorophyll a. Under electron microscopy, cell surface structures such as prosthecae and flagella are clearly visible, reflecting traits typical of marine Alphaproteobacteria adapted for surface attachment or motility in aquatic environments. A. arctica divides by binary fission, and no spore formation has been observed, consistent with other members of the Hyphomonadaceae family. The structural lipid composition of the cell membrane includes phosphatidylglycerol (PG), monogalactosyldiacylglycerol (MGDG), glucopyranosyl diacylglycerol (GUDG), and three unidentified phospholipids, which are typical of the genus Algimonas. The predominant respiratory quinone is ubiquinone-10 (Q-10) . The major fatty acids are C_18:1 ω7c (69.1%) and C_18:1 2-OH (18.7%), consistent with other members of the Hyphomonadaceae, which often display a higher proportion of glycolipids and sulfolipids relative to phospholipids.

Genomics

Genomic analysis of Algimonas arctica strain SM1216ᵀ indicates a DNA guanine and cytosine content of 60.6 mol%, higher than that of A. ampicilliniresistens (54.9 mol%) and A. porphyrae (58.5 mol%). To date, no complete genome assembly or detailed pathway annotations have been published for this species, including a lack of data entry per this bacterium on the KEGG database.

Metabolism

Algimonas arctica is a strictly aerobic, chemoorganotrophic bacterium, deriving energy from the oxidation of organic compounds in the presence of oxygen. The organism does not ferment carbohydrates and exhibits no growth under anaerobic conditions. Enzymatic and biochemical testing revealed that A. arctica is oxidase-positive and catalase-positive, indicating a functional electron transport chain for aerobic respiration. It can reduce nitrate to nitrite, suggesting that it may play a role in nitrogen cycling within its native Arctic intertidal ecosystem.

Carbohydrate metabolism is relatively limited but includes utilization of D-xylose, D-mannose, arbutin, and gentiobiose. The bacterium does not hydrolyze starch, gelatin, DNA, or Tween 80, and is negative for typical mixed-acid fermentation indicators such as the methyl red and Voges–Proskauer reactions. It also does not produce indole or hydrogen sulfide. Analysis using the API ZYM system, a lab test for enzymes, confirmed the presence of several hydrolytic enzymes, including esterase (C4), cystine arylamidase, acid phosphatase, and β-glucosidase, which suggest limited but targeted capacities for degrading complex molecules. Like other members of the family Hyphomonadaceae, A. arctica synthesizes ubiquinone-10 (Q-10) as its major respiratory quinone. Its fatty acid profile is dominated by C_18:1 ω7c and C_18:1 2-OH, monounsaturated fatty acids commonly found in cold-adapted marine bacteria, which contribute to membrane fluidity under low-temperature conditions.^[5]

Physiology

Algimonas arctica is a strictly aerobic, chemoorganotrophic bacterium that demonstrates a high degree of physiological adaptability to cold marine environments. It is capable of growth across a broad range of temperatures, from 4 °C to 30 °C, with optimal growth occurring at 25 °C. The organism grows in media with 0.5–6.0% NaCl, showing optimal tolerance at 2.0–3.0%, and displays pH tolerance from 5.0 to 9.0, preferring conditions between pH 7.0 and 8.0. The species tests positive for catalase and oxidase activity, indicating an oxidative metabolism. It is also capable of nitrate reduction to nitrite, a metabolic feature common among marine Alphaproteobacteria. In contrast, it does not hydrolyze starch, gelatin, DNA, or Tween 80, and does not produce hydrogen sulfide, indole, or utilize methyl red or Voges–Proskauer pathways. Enzymatic profiling using API ZYM assays shows activity for esterase (C4), cystine arylamidase, acid phosphatase, and β-glucosidase, among others. The bacterium can metabolize several carbohydrates, including D-xylose, D-mannose, arbutin, and gentiobiose, indicating moderate saccharolytic capabilities. The primary respiratory quinone in A. arctica is ubiquinone-10 (Q-10), consistent with other members of the family Hyphomonadaceae. Its major fatty acid components include C_18:1 ω7c and C_18:1 2-OH, which together account for over 85% of total fatty acid composition. These monounsaturated fatty acids are thought to contribute to membrane fluidity under cold environmental conditions. ^[5] Collectively, the physiological characteristics of A. arctica reflect adaptation to cold, oligotrophic, and saline marine environments, and align with the broader metabolic traits of the Hyphomonadaceae family.

Ecology and Scientific Relevance

Algimonas arctica is of growing interest in the study of polar microbial ecology, extremophile adaptation, and the potential development of biotechnological applications involving cold-active cellular processes. Although it is not currently used in applied science or medicine, its physiological and biochemical features make it relevant for both environmental monitoring and foundational microbiology research.

Isolated from intertidal sand in Kongsfjorden, Svalbard, A. arctica was recovered during the 8th Chinese National Arctic Scientific Expedition in 2011, from a cold, marine-influenced sediment environment shaped by glacial runoff and seasonal variation. This Arctic setting is known to support high microbial diversity, with metabolically active bacterial communities that help regulate organic carbon and nutrient cycling. The presence of A. arctica in this niche contributes to our understanding of how microbes adapt to low temperatures, variable salinity, and nutrient-limited conditions. The species displays several traits consistent with other extremophilic Alphaproteobacteria, including growth at 4–30 °C, tolerance of 0.5–6.0% NaCl, and a suite of lipids typical of cold-adapted marine bacteria. Its cellular membrane contains monoglycosyl diglyceride (MGDG), glucuronopyranosyl diglyceride (GUDG), and ubiquinone Q-10, which are commonly found in psychrotolerant and marine species within the family Hyphomonadaceae. These features may have future relevance in biotechnological applications, including the development of cold-active enzymes, biosurfactants, or cryoprotectants.

In addition, A. arctica exhibits an antibiotic resistance profile that includes resistance to ampicillin, vancomycin, and polymyxin B, while remaining susceptible to chloramphenicol and erythromycin. This characteristic could provide insight into intrinsic resistance mechanisms in polar environments and support further antimicrobial research. More broadly, A. arctica represents a model for studying how climate change may affect microbial life in Arctic coastal ecosystems. As glaciers retreat and nutrient regimes shift, Arctic microbes play a key role in ecosystem resilience and biogeochemical regulation. Continued research on bacteria such as A. arctica can help assess biodiversity loss and adaptation in response to environmental change.