Global Growth Phase Response of the Gut Bacterium Phocaeicola vulgatus (Phylum Bacteroidota).

INTRODUCTION: Phocaeicola vulgatus (basonym Bacteroides vulgatus) belongs to the intestinal microbiome of healthy humans and animals, where it participates in the fermentative breakdown of biopolymers ingested with food. In doing so, P. vulgatus contributes to the shaping of the gut metabolome, which benefits the host health. Moreover, considering the fermentation product range (short chain fatty acids), P. vulgatus suggests itself as a potential nonstandard platform organism for a sustainable production of basic organic chemicals. Complementing a recent physiologic-proteomic report deciphering the strain's versatile fermentation network, the present study focusses on the global growth phase-dependent response of P. vulgatus. METHODS: P. vulgatus was anaerobically cultivated with glucose as sole source of carbon and energy in process-controlled bioreactors operated in parallel. Close sampling was conducted to measure growth parameters (OD, CDW, ATP-content, substrate/product profiles) as basis for determining growth stoichiometry in detail. A coarser sampling (½ODmax, ODmax, and ODstat) served the molecular analysis of the global growth phase-dependent response, studied by means of differential proteomics (soluble and membrane fractions, nanoLC-ESI-MS/MS) as well as targeted metabolite (GC-MS and LC-MS/MS) and untargeted exometabolome (FT-ICR-MS) analyses. RESULTS: The determined growth performance of P. vulgatus features 1.74 h doubling time, 0.06 gCDW/mmolGlc biomass yield, 0.36 (succinate) and 0.61 (acetate) mmolP/mmolGlc as predominant fermentation product yields, and 0.43 mmolATP/mmolC as theoretically calculated ATP yield. The fermentation pathway displayed distinct growth phase-dependent dynamics: the levels of proteins and their accompanying metabolites constituting the upper part of glycolysis peaked at ½ODmax, whereas those of the lower part of glycolysis and of the fermentation routes in particular toward the predominant products acetate and succinate were highest at ODmax and ODstat. While identified proteins of monomer biosynthesis displayed rather unspecific profiles, most of the intracellular amino acids peaked at ODmax. By contrast, proteins and metabolites related to stress response and quorum sensing showed increased abundances at ODmax and ODstat. Finally, the composition of the exometabolome expanded from 2,317 molecular formulas at ½ODmax via 4,258 at ODmax to 4,501 at ODstat, with growth phase-specific subsets increasing in parallel. CONCLUSIONS: The present study provides insights into the distinct growth phase-dependent behavior of P. vulgatus during cultivation in bioreactors on the physiological and molecular levels. This could serve as a valuable knowledge-base for further developing P. vulgatus as a nonconventional platform organism for biotechnological applications. In addition, the findings shed new light on the potential growth phase-dependent imprints of P. vulgatus on the gut microbiome environment, e.g., by indicating interactions via quorum sensing and by unraveling the complex exometabolic background against which fermentation products and secondary metabolites are formed.

Microbes with higher metabolic independence are enriched in human gut microbiomes under stress.

A wide variety of human diseases are associated with loss of microbial diversity in the human gut, inspiring a great interest in the diagnostic or therapeutic potential of the microbiota. However, the ecological forces that drive diversity reduction in disease states remain unclear, rendering it difficult to ascertain the role of the microbiota in disease emergence or severity. One hypothesis to explain this phenomenon is that microbial diversity is diminished as disease states select for microbial populations that are more fit to survive environmental stress caused by inflammation or other host factors. Here, we tested this hypothesis on a large scale, by developing a software framework to quantify the enrichment of microbial metabolisms in complex metagenomes as a function of microbial diversity. We applied this framework to over 400 gut metagenomes from individuals who are healthy or diagnosed with inflammatory bowel disease (IBD). We found that high metabolic independence (HMI) is a distinguishing characteristic of microbial communities associated with individuals diagnosed with IBD. A classifier we trained using the normalized copy numbers of 33 HMI-associated metabolic modules not only distinguished states of health versus IBD, but also tracked the recovery of the gut microbiome following antibiotic treatment, suggesting that HMI is a hallmark of microbial communities in stressed gut environments.

Metabolic independence drives gut microbial colonization and resilience in health and disease.

BACKGROUND: Changes in microbial community composition as a function of human health and disease states have sparked remarkable interest in the human gut microbiome. However, establishing reproducible insights into the determinants of microbial succession in disease has been a formidable challenge. RESULTS: Here we use fecal microbiota transplantation (FMT) as an in natura experimental model to investigate the association between metabolic independence and resilience in stressed gut environments. Our genome-resolved metagenomics survey suggests that FMT serves as an environmental filter that favors populations with higher metabolic independence, the genomes of which encode complete metabolic modules to synthesize critical metabolites, including amino acids, nucleotides, and vitamins. Interestingly, we observe higher completion of the same biosynthetic pathways in microbes enriched in IBD patients. CONCLUSIONS: These observations suggest a general mechanism that underlies changes in diversity in perturbed gut environments and reveal taxon-independent markers of "dysbiosis" that may explain why widespread yet typically low-abundance members of healthy gut microbiomes can dominate under inflammatory conditions without any causal association with disease.

Adaptability as the key to success for the ubiquitous marine nitrite oxidizer Nitrococcus.

Nitrite-oxidizing bacteria (NOB) have conventionally been regarded as a highly specialized functional group responsible for the production of nitrate in the environment. However, recent culture-based studies suggest that they have the capacity to lead alternative lifestyles, but direct environmental evidence for the contribution of marine nitrite oxidizers to other processes has been lacking to date. We report on the alternative biogeochemical functions, worldwide distribution, and sometimes high abundance of the marine NOB Nitrococcus. These largely overlooked bacteria are capable of not only oxidizing nitrite but also reducing nitrate and producing nitrous oxide, an ozone-depleting agent and greenhouse gas. Furthermore, Nitrococcus can aerobically oxidize sulfide, thereby also engaging in the sulfur cycle. In the currently fast-changing global oceans, these findings highlight the potential functional switches these ubiquitous bacteria can perform in various biogeochemical cycles, each with distinct or even contrasting consequences.

Nitrite oxidation in the Namibian oxygen minimum zone.

Nitrite oxidation is the second step of nitrification. It is the primary source of oceanic nitrate, the predominant form of bioavailable nitrogen in the ocean. Despite its obvious importance, nitrite oxidation has rarely been investigated in marine settings. We determined nitrite oxidation rates directly in (15)N-incubation experiments and compared the rates with those of nitrate reduction to nitrite, ammonia oxidation, anammox, denitrification, as well as dissimilatory nitrate/nitrite reduction to ammonium in the Namibian oxygen minimum zone (OMZ). Nitrite oxidation (≤372 nM NO(2)(-) d(-1)) was detected throughout the OMZ even when in situ oxygen concentrations were low to non-detectable. Nitrite oxidation rates often exceeded ammonia oxidation rates, whereas nitrate reduction served as an alternative and significant source of nitrite. Nitrite oxidation and anammox co-occurred in these oxygen-deficient waters, suggesting that nitrite-oxidizing bacteria (NOB) likely compete with anammox bacteria for nitrite when substrate availability became low. Among all of the known NOB genera targeted via catalyzed reporter deposition fluorescence in situ hybridization, only Nitrospina and Nitrococcus were detectable in the Namibian OMZ samples investigated. These NOB were abundant throughout the OMZ and contributed up to ~9% of total microbial community. Our combined results reveal that a considerable fraction of the recently recycled nitrogen or reduced NO(3)(-) was re-oxidized back to NO(3)(-) via nitrite oxidation, instead of being lost from the system through the anammox or denitrification pathways.