Effect of large magnetotactic bacteria with polyphosphate inclusions on the phosphate profile of the suboxic zone in the Black Sea.

The Black Sea is the world's largest anoxic basin and a model system for studying processes across redox gradients. In between the oxic surface and the deeper sulfidic waters there is an unusually broad layer of 10-40 m, where neither oxygen nor sulfide are detectable. In this suboxic zone, dissolved phosphate profiles display a pronounced minimum at the upper and a maximum at the lower boundary, with a peak of particulate phosphorus in between, which was suggested to be caused by the sorption of phosphate on sinking particles of metal oxides. Here we show that bacterial polyphosphate inclusions within large magnetotactic bacteria related to the genus Magnetococcus contribute substantially to the observed phosphorus peak, as they contain 26-34% phosphorus compared to only 1-5% in metal-rich particles. Furthermore, we found increased gene expression for polyphosphate kinases by several groups of bacteria including Magnetococcaceae at the phosphate maximum, indicating active bacterial polyphosphate degradation. We propose that large magnetotactic bacteria shuttle up and down within the suboxic zone, scavenging phosphate at the upper and releasing it at the lower boundary. In contrast to a passive transport via metal oxides, this bacterial transport can quantitatively explain the observed phosphate profiles.

New insights into the role of the porcine intestinal yeast, Kazachstania slooffiae, in intestinal environment of weaned piglets.

Kazachstania slooffiae is a porcine intestinal yeast whose role in the intestinal environment is largely unexplored. Therefore, the impact of K. slooffiae on growth performance, intestinal microbial metabolites and the microbiota of weaned piglets was investigated in this study. Forty-eight German Landrace pigs were weaned at day 27 or 28 of life and grouped into one control and three treatment groups. During the 5-week experiment, piglets had ad libitum access to feed and water. On days 5, 6 and 7 post weaning, pigs were orally supplemented with either placebo or K. slooffiae cells once a day. Faecal samples collected on days 5-8, 14, 21 and 28 post weaning were used for microbiological and chemical analyses. Between groups, there were no significant differences in the incidence of diarrhoea, pH and growth performance. Total yeasts and K. slooffiae correlated positively with total short-chain fatty acids, acetic, propionic, n-butyric, i-valeric and valeric acids, and negatively with pH. Pyrosequencing of the bacterial intestinal community revealed that K. slooffiae significantly affected the composition of the microbiota. The results of this study suggest that K. slooffiae may play an important role in the porcine digestive system, especially in the critical weaning period.

Comparative analysis of the fecal bacterial community of five harbor seals (Phoca vitulina).

The gut microbiota has many beneficial effects on host metabolism and health, and its composition is determined by numerous factors. It is also assumed that there was a co-evolution of mammals and the bacteria inhabiting their gut. Current knowledge of the mammalian gut microbiota mainly derives from studies on humans and terrestrial animals, whereas those on marine mammals are sparse. However, they could provide additional information on influencing factors, such as the role of diet and co-evolution with the host. In this study, we investigated and compared the bacterial diversity in the feces of five male harbor seals (Phoca vitulina). Because this small population included two half-brother pairs, each sharing a common father, it allowed an evaluation of the impact of host relatedness or genetic similarity on the gut microbial community. Fresh feces obtained from the seals by an enema were analyzed by fluorescence in situ hybridization and amplicon sequencing of 16S rRNA genes. The results showed that the bacterial communities in the seals' feces mainly consisted of the phyla Firmicutes (19-43%), Bacteroidetes (22-36%), Fusobacteria (18-32%), and Proteobacteria (5-17%) . Twenty-one bacterial members present in the fecal samples of the five seals contributed an average relative abundance of 93.7 + 8.7% of the total fecal microbial community. Contrary to all expectations based on previous studies a comparison of the fecal community between individual seals showed a higher similarity between unrelated than related individuals.

Uncoupling of bacterial and terrigenous dissolved organic matter dynamics in decomposition experiments.

The biodegradability of terrigenous dissolved organic matter (tDOM) exported to the sea has a major impact on the global carbon cycle, but our understanding of tDOM bioavailability is fragmentary. In this study, the effects of preparative tDOM isolation on microbial decomposition were investigated in incubation experiments consisting of mesocosms containing mesohaline water from the Baltic Sea. Dissolved organic carbon (DOC) consumption, molecular DOM composition, bacterial activities, and shifts in bacterial community structure were compared between mesocosms supplemented with riverine tDOM, either as filtered, particle-free river water or as a concentrate obtained by lyophilization/tangential ultrafiltration, and those containing only Baltic Sea water or river water. As shown using ultra-high-resolution mass spectrometry (15 Tesla Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) covering approximately 4600 different DOM compounds, the three DOM preparation protocols resulted in distinct patterns of molecular DOM composition. However, despite DOC losses of 4-16% and considerable bacterial production, there was no significant change in DOM composition during the 28-day experiment. Moreover, tDOM addition affected neither DOC degradation nor bacterial dynamics significantly, regardless of the tDOM preparation. This result suggested that the introduced tDOM was largely not bioavailable, at least on the temporal scale of our experiment, and that the observed bacterial activity and DOC decomposition mainly reflected the degradation of unknown, labile, colloidal and low-molecular weight DOM, both of which escape the analytical window of FT-ICR-MS. In contrast to the different tDOM preparations, the initial bacterial inoculum and batch culture conditions determined bacterial community succession and superseded the effects of tDOM addition. The uncoupling of tDOM and bacterial dynamics suggests that mesohaline bacterial communities cannot efficiently utilize tDOM and that in subarctic estuaries other factors are responsible for the removal of imported tDOM.