Microbial succession on lignite along with weathering was examined by scanning electron microscopy (SEM). Few microorganisms were observed on lignite samples just excavated and only spores and short hyphae were observed on lignite samples excavated 5 months, 1 year and 4 years before sampling. When lignite samples were moistened with distilled water and incubated for 10 days, actinomycetes proliferated significantly on lignite samples that were just excavated or excavated 5 months before sampling. The growth of bacteria was observed on lignite samples excavated 1 year before sampling. Fungi increased in length and in number on lignite samples excavated 4 years before sampling. These findings of microbial succession on lignite samples along with weathering were consistent with results of the plate count method; actinomycetes are the first colonizers, then bacteria and fungi are the last.

View full abstract

Mechanisms of lignite solubilization were investigated to understand the microbial succession in lignite piles along with weathering after excavation. Solubilization of lignite by phosphate buffer was significantly increased with increases in buffer pH. Chelation of iron was involved in solubilization of lignite, though it was less effective than pH increase. Reduction of iron was another important process for solubilizing lignite.
When lignite samples were incubated, greater solubilization occurred under anaerobic conditions than under aerobic conditions. Increase in pH were also an important process, especially for newly excavated lignite samples, while the reduction process was important for more weathered lignite samples. Microbial solubilization/degradation of lignite is considered to occur by complex processes cooperating at anaerobic spots and aerobic sites in lignite piles; anaerobic conditions accelerate lignite solubilization and thus solubilized lignite is utilized by microorganisms at aerobic sites.

View full abstract

A flow cytometer was used to measure the intracellular RNA contents of Vibrio alginolyticus and natural bacterial populations after specific staining with acridine orange. During the course of starvation, the RNA level in Vibrio alginolyticus gradually decreased, whereas subsequent enrichment caused a rapid increment of RNA and resulted in the appearance of a distinct group on the cytometric histogram. Similar distinct subpopulations were also confirmed in natural seawater samples after 6 hours direct viable count (DVC) incubation. Moreover, it was confirmed that the DVC technique enabled us to detect and enumerate marine bacteria using 16S rRNA fluorescent oligonucleotide probes.

View full abstract