Department of Molecular Ecology, Max Planck Institute for Marine Microbiology, Bremen D-28359, Germany.
Institute of Chemistry and Biology of the Marine Environment, University of Oldenburg, Wilhelmshafen, Germany.
ISME J. 2024 Jan 8;18(1). doi: 10.1093/ismejo/wrae155.
One of the most hostile marine habitats on Earth is the surface of the South Pacific Gyre (SPG), characterized by high solar radiation, extreme nutrient depletion, and low productivity. During the SO-245 "UltraPac" cruise through the center of the ultra-oligotrophic SPG, the marine alphaproteobacterial group AEGEAN169 was detected by fluorescence in situ hybridization at relative abundances up to 6% of the total microbial community in the uppermost water layer, with two distinct populations (Candidatus Nemonibacter and Ca. Indicimonas). The high frequency of dividing cells combined with high transcript levels suggests that both clades may be highly metabolically active. Comparative metagenomic and metatranscriptomic analyses of AEGEAN169 revealed that they encoded subtle but distinct metabolic adaptions to this extreme environment in comparison to their competitors SAR11, SAR86, SAR116, and Prochlorococcus. Both AEGEAN169 clades had the highest percentage of transporters per predicted proteins (9.5% and 10.6%, respectively). In particular, the high expression of ABC transporters in combination with proteorhodopsins and the catabolic pathways detected suggest a potential scavenging lifestyle for both AEGEAN169 clades. Although both AEGEAN169 clades may share the genomic potential to utilize phosphonates as a phosphorus source, they differ in their metabolic pathways for carbon and nitrogen. Ca. Nemonibacter potentially use glycine-betaine, whereas Ca. Indicimonas may catabolize urea, creatine, and fucose. In conclusion, the different potential metabolic strategies of both clades suggest that both are well adapted to thrive resource-limited conditions and compete well with other dominant microbial clades in the uppermost layers of SPG surface waters.
地球上最具挑战性的海洋生境之一是南太平洋 Gyre（SPG）的表面，其特点是太阳辐射强、极度营养匮乏和生产力低。在 SO-245“UltraPac”考察穿越超寡营养的 SPG 中心期间，通过荧光原位杂交检测到海洋 α 变形菌纲 AEGEAN169，在最上层水体中的总微生物群落中相对丰度高达 6%，有两个不同的种群（疑似 Nemonibacter 和疑似 Indicimonas）。分裂细胞的高频率加上高转录水平表明，这两个分支可能具有高度的代谢活性。AEGEAN169 的比较宏基因组和宏转录组分析表明，与竞争微生物 SAR11、SAR86、SAR116 和聚球藻相比，它们编码了微妙但明显的代谢适应这种极端环境的能力。AEGEAN169 的两个分支都具有每预测蛋白最高的转运蛋白百分比（分别为 9.5%和 10.6%）。特别是，ABC 转运蛋白的高表达与质体视蛋白和检测到的分解代谢途径相结合，表明这两个分支都可能具有潜在的掠夺性生活方式。尽管 AEGEAN169 的两个分支可能具有利用膦酸盐作为磷源的基因组潜力，但它们在碳和氮的代谢途径上存在差异。疑似 Nemonibacter 可能利用甘氨酸甜菜碱，而疑似 Indicimonas 可能分解尿素、肌酸和岩藻糖。总之，两个分支的不同潜在代谢策略表明，它们都很好地适应了资源有限的条件，并与 SPG 表面水最上层的其他优势微生物分支竞争良好。
