Significance: A number of organisms synthesize hydrocarbons, but the scale at which this occurs in the environment is unknown. Here, we provide the first global estimates of hydrocarbon production by the two most abundant cyanobacteria on Earth, Prochlorococcus and Synechococcus . We suggest that these organisms represent a significant and widespread source of hydrocarbons to the world’s oceans, which in turn may sustain populations of obligate hydrocarbon-degrading bacteria known to be important in consuming anthropogenic oil spills. Our study demonstrates the role cyanobacteria play in the ocean ‟hydrocarbon cycle” and reveals the massive scale of this process. The widespread distribution of cyanobacteria and hydrocarbon-degrading bacteria in freshwater, marine, and terrestrial environments suggests the hydrocarbon cycle is pervasive in many natural ecosystems.

A Golden Gate-based assembly standard developed for cloning and transformation in cyanobacteria is compatible with, and builds on, the broadly established plant

The Mariana Trench is the deepest known site in the Earth’s oceans, reaching a depth of ~ 11,000 m at the Challenger Deep. Recent studies reveal that hadal waters harbor distinctive microbial planktonic communities. However, the genetic potential of microbial communities within the hadal zone is poorly understood. Here, implementing both culture-dependent and culture-independent methods, we perform extensive analysis of microbial populations and their genetic potential at different depths in the Mariana Trench. Unexpectedly, we observed an abrupt increase in the abundance of hydrocarbon-degrading bacteria at depths > 10,400 m in the Challenger Deep. Indeed, the proportion of hydrocarbon-degrading bacteria at > 10,400 m is the highest observed in any natural environment on Earth. These bacteria were mainly Oleibacter, Thalassolituus, and Alcanivorax genera, all of which include species known to consume aliphatic hydrocarbons. This community shift towards hydrocarbon degraders was accompanied by increased abundance and transcription of genes involved in alkane degradation. Correspondingly, three Alcanivorax species that were isolated from 10,400 m water supplemented with hexadecane were able to efficiently degrade n-alkanes under conditions simulating the deep sea, as did a reference Oleibacter strain cultured at atmospheric pressure. Abundant n-alkanes were observed in sinking particles at 2000, 4000, and 6000 m (averaged 23.5 μg/gdw) and hadal surface sediments at depths of 10,908, 10,909, and 10,911 m (averaged 2.3 μg/gdw). The δ2H values of n-C16/18 alkanes that dominated surface sediments at near 11,000-m depths ranged from − 79 to − 93‰, suggesting that these sedimentary alkanes may have been derived from an unknown heterotrophic source. These results reveal that hydrocarbon-degrading microorganisms are present in great abundance in the deepest seawater on Earth and shed a new light on potential biological processes in this extreme environment.

The aerobic electron transport chain in Mycobacterium smegmatis can terminate in one of three possible terminal oxidase complexes. The structure and function of the electron transport pathway leading from the menaquinol-menaquinone pool to the cytochrome bc ₁ complex and terminating in the aa ₃ -type cytochrome c oxidase was characterized. M. smegmatis strains with mutations in the bc ₁ complex and in subunit II of cyctochome c oxidase were found to be profoundly growth impaired, confirming the importance of this respiratory pathway for mycobacterial growth under aerobic conditions. Disruption of this pathway resulted in an adaptation of the respiratory network that is characterized by a marked up-regulation of cydAB , which encodes the bioenergetically less efficient and microaerobically induced cytochrome bd -type menaquinol oxidase that is required for the growth of M. smegmatis under O ₂ -limiting conditions. Further insights into the adaptation of this organism to rerouting of the electron flux through the branch terminating in the bd -type oxidase were revealed by expression profiling of the bc ₁ -deficient mutant strain using a partial-genome microarray of M. smegmatis that is enriched in essential genes. Although the expression profile was indicative of an increase in the reduced state of the respiratory chain, blockage of the bc ₁ - aa ₃ pathway did not induce the sentinel genes of M. smegmatis that are induced by oxygen starvation and are regulated by the DosR two-component regulator.