■生物固氮(BNF),地球上的活微生物中无与伦比的代谢新颖性,全球对自然生态系统的贡献约为88-101TgN年-1,约56%来自共生BNF,而约22-45%来自自由生活的固氮剂(FLNF)。共生BNF的成功很大程度上取决于其与寄主植物的相互作用,然而,无处不在的环境异养FLNFs在其直接生态位维持不受阻碍的BNF方面面临许多限制。自养型FLNFs,如蓝细菌和海洋异养重氮生物,已经对它们的发明进行了充分的研究,这些生物适应/适应了这些生物,以胜过功能性重氮营养的环境限制。然而,FLNF异养生物在紧张的河口/海洋/水生生境下执行BNF时面临更多的逆境。
■在这项研究中,对190个NCBI接入和45个未接入的异养FLNF可培养细菌分离株(共235株)进行了大规模的培养依赖性调查,这些分离株来自印度Sundarbans的嗜盐河口潮间带红树林,拉姆萨尔遗址和联合国教科文组织宣布为世界遗产。假设微生物群落的可培养性~1%,还通过V3-V4rRNA区域的培养无关的下一代测序研究了各自的生态位代表实际的细菌多样性.
■两项研究都显示出更高的可培养的伽玛变形菌丰度,其次是Firmicutes,研究的235种FLNFs中的大多数属于这两类。FLNFs在游离氮固定剂和铁氧化细菌的培养基中显示出相当的选择潜力,将重氮营养与铁氧化联系起来,铁载体生产,磷溶解,磷的吸收和积累以及反硝化。
■这一观察结果验证了在极端河口红树林生态位下的假设,重氮生物被自然选择为专门的多维实体,加快BNF和生存。来自红树林生态位的早期宏基因组数据证明了C之间的微生物代谢耦合,N,P,S,和红树林沉积物中的铁循环,作为一种适应性特征,与共同丰富的各自的功能基因很明显,这证实了我们在具有挑战性的潮间带红树林环境中多种相互关联的代谢潜力促进BNF的培养模式中的发现。
UNASSIGNED: Biological nitrogen fixation (BNF), an unparalleled metabolic novelty among living microorganisms on earth, globally contributes ~88-101 Tg N year-1 to natural ecosystems, ~56% sourced from symbiotic BNF while ~22-45% derived from free-living nitrogen fixers (FLNF). The success of symbiotic BNF is largely dependent on its interaction with host-plant, however ubiquitous environmental heterotrophic FLNFs face many limitations in their immediate ecological niches to sustain unhindered BNF. The autotrophic FLNFs like cyanobacteria and oceanic heterotrophic diazotrophs have been well studied about their contrivances acclimated/adapted by these organisms to outwit the environmental constraints for functional diazotrophy. However, FLNF heterotrophs face more adversity in executing BNF under stressful estuarine/marine/aquatic habitats.
UNASSIGNED: In this study a large-scale cultivation-dependent investigation was accomplished with 190 NCBI accessioned and 45 non-accessioned heterotrophic FLNF cultivable bacterial isolates (total 235) from halophilic estuarine intertidal mangrove niches of Indian Sundarbans, a Ramsar site and UNESCO proclaimed World Heritage Site. Assuming ~1% culturability of the microbial community, the respective niches were also studied for representing actual bacterial diversity via cultivation-independent next-generation sequencing of V3-V4 rRNA regions.
UNASSIGNED: Both the studies revealed a higher abundance of culturable Gammaproteobacteria followed by Firmicutes, the majority of 235 FLNFs studied belonging to these two classes. The FLNFs displayed comparable selection potential in media for free nitrogen fixers and iron-oxidizing bacteria, linking diazotrophy with iron oxidation, siderophore production, phosphorus solubilization, phosphorus uptake and accumulation as well as denitrification.
UNASSIGNED: This observation validated the hypothesis that under extreme estuarine mangrove niches, diazotrophs are naturally selected as a specialized multidimensional entity, to expedite BNF and survive. Earlier metagenome data from mangrove niches demonstrated a microbial metabolic coupling among C, N, P, S, and Fe cycling in mangrove sediments, as an adaptive trait, evident with the co-abundant respective functional genes, which corroborates our findings in cultivation mode for multiple interrelated metabolic potential facilitating BNF in a challenging intertidal mangrove environment.