The diversity and ecological significance of microbial traits potentially involved in B_(12) biosynthesis in the global ocean

Cobalamin(B_(12)),an essential nutrient and growth cofactor for many living organisms on Earth,can be fully synthesized only by selected prokaryotes in nature.Therefore,microbial communities related to B_(12) biosynthesis could serve as an example subsystem to disentangle the underlying ecological mechanisms balancing the function and taxonomic make-up of complex functional assemblages.By anchoring microbial traits potentially involved in B_(12) biosynthesis,we depict the biogeographic patterns of B_(12) biosynthesis genes and the taxa harboring them in the global ocean,despite the limitations of detecting de novo B_(12) synthesizers via metagenomes alone.Both the taxonomic and functional composition of B_(12) biosynthesis genes were strongly shaped by depth,differentiating the epipelagic zones from the mesopelagic layers.Functional genes related to B_(12) biosynthesis were relatively stably distributed across different oceans,but the taxa harboring them varied considerably,showing clear functional redundancy among microbial systems.Microbial taxa carrying B_(12) biosynthesis genes in the surface water were influenced by environmental factors such as temperature,oxygen,and nitrate.However,the composition of functional genes was only weakly associated with these environmental factors.Null model analyses demonstrated that determinism governed the variations in B_(12) biosynthesis genes,whereas a higher degree of stochasticity was associated with taxonomic variations.Significant associations were observed between the chlorophyll a concentration and B_(12) biosynthesis,confirming its importance in primary production in the global ocean.The results of this study reveal an essential ecological mechanism governing the assembly of microbes in nature:the environment selects for function rather than taxonomy;functional redundancy underlies stochastic community assembly.

Dissipative Kerr single soliton generation with extremely high probability via spectral mode depletion

Optical Kerr solitons generation based on microresonators is essential in nonlinear optics.Among various soliton generation processes,the single soliton generation plays a pivotal role since it ensures rigorous mode-locking on each comb line whose interval equals the free spectral range(FSR)of the microresonator.Current studies show that single soliton generation is challenging due to cavity instability.Here,we propose a new method to greatly improve single soliton generation probalility in the anomalous group velocity dispersion(GVD)regime in a micro-ring resonator based on silicon nitride.The improvement is realized by introducing mode depletion through an integrated coupled flter.It is convenient to introduce controllable single mode depletion in a micro-ring resonator by adjusting the response function of a coupled flter.We show that spectral mode depletion(SMD)can signifcantly boost the single soliton generation probability.The efect of SMD on the dynamics of optical Kerr solitons generation are also discussed.The proposed method ofers a straightforward and simple way to facilitate robust single soliton generation,and will have an impact on the research development in optical Kerr soliton generation and on-chip optical frequency mode manipulation.