Changes in morphology and metabolism enable Mn-oxidizing bacteria from mid-oceanic ridge environment to counter metal-induced stress.

Mn-oxidizing potential of two metal-tolerant bacterial strains - Halomonas meridiana and Marinobacter algicola isolated from the South West Indian Ridge waters were compared at varying concentrations of Mn (II), i.e., 1, 10, and 100 µmol and mmol L-1 . Accompanying changes in their morphology and metabolism were also determined. At concentrations >1 mmol L-1 Mn (II), Mn-oxidizing potential of M. algicola was 2-7 times greater than that of H. meridiana. Scanning electron microscopy revealed that exposure to elevated metal content prompted bacterial cells especially those of M. algicola to been enveloped in exopolymeric material and form aggregates. Energy dispersive spectrometric analysis showed that exopolymeric material acts as a nucleation site for Mn deposition and oxide formation which occurs in the form of microspherical aggregates. These features show striking resemblance to biogenically produced Fe-Mn oxide deposits from Lau Basin. Surprisingly, diffractograms of auto-oxidized and bacterially formed Mn-oxide showed similarities to the hydrothermal vein mineral Rhodochrosite indicating that it can also be produced biotically. Elongation of cells by up to 4× the original size and distortion in cell shape were evident at Mn (II) concentrations >100 µmol L-1 . Marked differences in C-substrate utilization by the test strains were also observed in presence of Mn (II). A shift in use of substrates that are readily available in oceanic waters like N-acetyl-d-glucosamine to those that can be used under changing redox conditions (d-cellobiose) or in the presence of metal ions (d-arabinose, l-asparagine) were observed. These findings highlight the significant role of autochthonous bacteria in transforming reduced metal ions and aiding in the formation of metal oxides. Under natural or laboratory conditions, the mode of bacterially generated Mn-oxide tends to remain the same.

Fluctuation of microbial activities after influent load variations in a full-scale SBR: recovery of the biomass after starvation.

Due to variations in the production levels, a full-scale sequencing batch reactor (SBR) for post-treatment of tannery wastewater was exposed to low and high ammonia load periods. In order to study how these changes affected the N-removal capacity, the microbiology of the reactor was studied by a diverse set of techniques including molecular tools, activity tests, and microbial counts in samples taken along 3 years. The recover capacity of the biomass was also studied in a lab-scale reactor operated with intermittent aeration without feeding for 36 days. The results showed that changes in the feeding negatively affected the nitrifying community, but the nitrogen removal efficiencies could be restored after the concentration stress. Species substitution was observed within the nitrifying bacteria, Nitrosomonas europaea and Nitrobacter predominated initially, and after an ammonia overload period, Nitrosomonas nitrosa and Nitrospira became dominant. Some denitrifiers, with nirS related to Alicycliphilus, Azospirillum, and Marinobacter nirS, persisted during long-term reactor operation, but the community fluctuated both in composition and in abundance. This fluctuating community may better resist the continuous changes in the feeding regime. Our results showed that a nitrifying-denitrifying SBR could be operated with low loads or even without feeding during production shut down periods.

Marinobacter gudaonensis sp. nov., isolated from an oil-polluted saline soil in a Chinese oilfield.

Two novel strains, SL014B61A(T) and SL014B11A, were isolated from an oil-polluted saline soil from Gudao in the coastal Shengli Oilfield, eastern China. Cells of strains SL014B61A(T) and SL014B11A were motile, Gram-negative and rod-shaped. Growth occurred at NaCl concentrations of between 0 and 15 % and at temperatures of between 10 and 45 degrees C. Strain SL014B61A(T) had Q9 as the major respiratory quinone and C16 : 0 (21.2 %), C18 : 1omega9c (20.3 %), C16 : 1omega7c (7.3 %) and C16 : 1omega9c (6.4 %) as predominant fatty acids. The G+C content of the DNA was 57.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain SL014B61A(T) belonged to the genus Marinobacter in the class Gammaproteobacteria. Strain SL014B61A(T) showed the highest 16S rRNA gene sequence similarity with Marinobacter bryozoorum (97.9 %) and showed 97.8 % sequence similarity to Marinobacter lipolyticus. DNA-DNA relatedness to the reference strains Marinobacter bryozoorum and Marinobacter lipolyticus was 35.5 % and 33.8 %, respectively. On the basis of these data, it is proposed that strains SL014B61A(T) and SL014B11A represent a novel species, Marinobacter gudaonensis sp. nov. The type strain is strain SL014B61A(T) (=DSM 18066(T)=LMG 23509(T)=CGMCC 1.6294(T)).

Marinobacter vinifirmus sp. nov., a moderately halophilic bacterium isolated from a wine-barrel-decalcification wastewater.

A halophilic, Gram-negative, motile, non-sporulating bacterium designated strain FB1T was isolated from a wine-barrel-decalcification wastewater. The organism comprises straight rods and has a strictly respiratory metabolism with O2. Strain FB1T grows optimally at 20-30 degrees C and 5-6% NaCl. The predominant fatty acids were found to be C18:1omega9c (30.4%), C16:0 (25.7%), C12:0 3-OH (10.3%), C16:1omega9c (9.7%) and C16:1omega7c (8.4%). A phylogenetic analysis based on 16S rRNA gene sequences revealed that the strain forms a coherent cluster within the genus Marinobacter. The highest level of 16S rRNA gene sequence similarity (97.9%) exhibited by strain FB1T was with the type strain of Marinobacter excellens. However, the level of DNA-DNA relatedness between the novel strain and M. excellens CIP 107,686T was only 31.2%. The DNA G+C content of strain FB1T was 58.7 mol%. On the basis of phenotypic and genotypic characteristics, and also phylogenetic evidence, strain FB1T is considered to represent a novel species of the genus Marinobacter, for which the name Marinobacter vinifirmus sp. nov. is proposed. The type strain is FB1T (=DSM 17747T=CCUG 52119T).

Marinobacter koreensis sp. nov., isolated from sea sand in Korea.

A marine, Gram-negative, aerobic, motile, straight-rod-shaped, moderately halophilic bacterium, designated strain DD-M3T, was isolated from sea sand in Pohang, Korea. A phylogenetic tree based on 16S rRNA gene sequences showed that the strain fell within the evolutionary radiation encompassed by the genus Marinobacter. The levels of 16S rRNA gene sequence similarity between the novel strain and the type strains of recognized Marinobacter species ranged from 94.2 to 97.6%, the highest values being with Marinobacter flavimaris SW-145T (97.6%) and Marinobacter lipolyticus SM19T (96.8%). The values for DNA-DNA relatedness between isolate DD-M3T and the type strains of the most closely related species, M. flavimaris and M. lipolyticus, were 41 and 36%, respectively. Strain DD-M3T was characterized as having Q-9 as the predominant respiratory quinone and 16:0, summed feature 3 and 18:1omega9c as the main fatty acids. The DNA G+C content was 54.1 mol%. On the basis of its phenotypic and genotypic characteristics, DD-M3T represents a novel species of the genus Marinobacter, for which the name Marinobacter koreensis sp. nov. is proposed, with DD-M3T (=KACC 11513T=DSM 17924T) as the type strain.