Changes in bacterial community metabolism and composition during the degradation of dissolved organic matter from the jellyfish Aurelia aurita in a Mediterranean coastal lagoon.

Spatial increases and temporal shifts in outbreaks of gelatinous plankton have been observed over the past several decades in many estuarine and coastal ecosystems. The effects of these blooms on marine ecosystem functioning and particularly on the dynamics of the heterotrophic bacteria are still unclear. The response of the bacterial community from a Mediterranean coastal lagoon to the addition of dissolved organic matter (DOM) from the jellyfish Aurelia aurita, corresponding to an enrichment of dissolved organic carbon (DOC) by 1.4, was assessed for 22 days in microcosms (8 l). The high bioavailability of this material led to (i) a rapid mineralization of the DOC and dissolved organic nitrogen from the jellyfish and (ii) the accumulation of high concentrations of ammonium and orthophosphate in the water column. DOM from jellyfish greatly stimulated heterotrophic prokaryotic production and respiration rates during the first 2 days; then, these activities showed a continuous decay until reaching those measured in the control microcosms (lagoon water only) at the end of the experiment. Bacterial growth efficiency remained below 20%, indicating that most of the DOM was respired and a minor part was channeled to biomass production. Changes in bacterial diversity were assessed by tag pyrosequencing of partial bacterial 16S rRNA genes, DNA fingerprints, and a cultivation approach. While bacterial diversity in control microcosms showed little changes during the experiment, the addition of DOM from the jellyfish induced a rapid growth of Pseudoalteromonas and Vibrio species that were isolated. After 9 days, the bacterial community was dominated by Bacteroidetes, which appeared more adapted to metabolize high-molecular-weight DOM. At the end of the experiment, the bacterial community shifted toward a higher proportion of Alphaproteobacteria. Resilience of the bacterial community after the addition of DOM from the jellyfish was higher for metabolic functions than diversity, suggesting that jellyfish blooms can induce durable changes in the bacterial community structure in coastal lagoons.

Biodegradation of crude oil by an Arctic psychrotrophic bacterium Pseudoalteromomas sp. P29.

A psychrotrophic petroleum-degrading bacterium Pseudoalteromonas sp. P29 was isolated from marine sediment, which was collected during 2nd Chinese Arctic Scientific Expedition. The phenotypic character and biodegradation efficiency on mixed oil or vacuum oil were tested at low temperature. The strain Pseudoalteromonas sp. P29 grew in a range of temperature from 5 to 35 degrees C and the optimum temperature was 25 degrees C. Gas chromatography analysis indicated that the strain might preferentially metabolize shorter-chain alkanes. The biodegradation efficiency were nearly 90 and 80%, respectively, after incubation at 5 degrees C for 28 days in the mineral medium supplement with mixed oil or vacuum oil as the sole carbon and energy source. The results showed a possible exploitation of the strain in future biotechnological processes especially in cold contaminated environments.

Environmental stress determines the quality of bacterial lysate and its utilization efficiency in a simple microbial loop.

Heterotrophic bacteria provide the critical link in the microbial loop by converting dissolved organic matter (DOM) into particulate form. In this study, DOM was prepared from recently isolated estuarine bacterial strain Vibrio sp. (DSM14379) grown at different salinities [0.2%, 0.5%, 3%, 5%, or 10% (w/v)], washed, concentrated, and lysed by autoclaving. The corresponding lysate-containing media were designated LM(0.2), LM(0.5), LM(3), LM(5), and LM(10). Vibrio sp. cells grown at different salinities had similar C/N/P ratios, but different C/S ratios, different trace element composition, and different 2D gel electrophoresis protein profiles. Pseudoalteromonas sp. (DSM06238) isolated from a similar environment was able to grow on all lysates, and its biomass production was dependent on lysate type. The highest growth rate and biomass production of Pseudoalteromonas sp. at saturation lysate concentrations were observed in LM(3). The biomass production at saturation lysate concentrations was about 3-fold higher as compared to LM(0.2) and LM(10). The initial respiration rate, intracellular adenosine triphosphate (ATP) levels, and (3)H-Leu and (3)H-TdR incorporation rates were lowest in LM(3). On the other hand, in LM(0.2) or LM(10) lysates the situation was reversed, the growth rates and biomass production were lowest, whereas (3)H-Leu and (3)H-TdR incorporation, respiration rates, as well as ATP levels, were highest. These results imply uncoupling of catabolism from growth in either high- or low-salinity lysates. The results also suggest that differences in organic carbon quality generated during Vibrio sp. growth at different NaCl concentrations were propagated through the simple microbial loop, which may have important ecological implications for higher trophic levels that depend on microbial grazing.

The nature of plant growth-promoting effects of a pseudoalteromonad associated with the marine algae Laminaria japonica and linked to catalase excretion.

AIMS: The goal of this study was to identify a marine algae-associated bacterium isolated from Laminaria japonica and investigate this microorganism's growth-promoting effects on plants. METHODS AND RESULTS: The bacterium, identified as Pseudoalteromonas porphyrae, was determined to display a biostimulatory activity for seed germination and shoot growth in several agricultural plants and also for growth in ginseng callus cell culture. This biostimulatory activity was linked to a catalase enzyme that was excreted in the maximal amount during the transition from logarithmic growth phase to stationary growth phase. In addition, selected shifts in growth temperature and medium salinity affected the amount of enzyme excreted. The purified catalase was determined to be composed of identical subunits. The catalase of interest displayed significantly higher biostimulatory activity than the catalase from bovine liver. CONCLUSIONS: The catalase investigated in this study is unique in that it promotes growth in and possibly contributes to stress tolerance of plants. SIGNIFICANCE AND IMPACT OF THE STUDY: The catalase of interest has the potential for use in treatments that aim to improve percent seed germination as well as obtaining tall shoots in a shorter time period.