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Bacterial community succession corresponds to changes in the phylogenetic identity, growth-response time and rRNA operon (rrn) copy number of culturable populations. To test this hypothesis, we compared the bacterial fractions culturable from the oxic zone of flooded, unplanted paddy soil microcosms after 1-day (early succession) and 70-day (late succession) incubation periods. The proportion of bacteria that was cultivable on solid media corresponded for early and late succession to 3740% and 3135% of total DAPI cell counts, which were 7.40 (±0.36) × 108 and 5.54 (±0.28) × 108 cells per gram of dry soil, respectively. In colony-forming curve analysis, late successional bacteria showed a significant delay in their growth response compared with those from early succession. A total of 59 early successional isolates grouped into 16 species-level clusters (SLC) plus three Bacilli-like SLC, while 66 late successional isolates formed 25 SLC plus five Bacilli-like SLC. Except Bacilli-like spp., isolates from early succession always belonged to different SLC than those from late succession. Betaproteobacteria and Gammaproteobacteria were typical of the early stage, while Alphaproteobacteria and Actinobacteria prevailed in late succession. Considering all SLC except those assigned to Bacilli, growth-response time and rrn copy number were significantly correlated with successional stage. Isolates of most early successional SLC (14 of 16) formed visible colonies within 1 (11 SLC) or 2 days (three SLC) and contained = 4 rrn copies. In contrast, isolates of late successional SLC (23 of 25) formed visible colonies within 2 days (four SLC) or, in most cases, only within 315 days (19 SLC) and contained = 2 rrn copies. Regardless of whether isolated from early or late succession, Bacilli-like isolates always showed a colony-forming time of 2 days and had 911 rrn copies.
Quantification of microbial load in diesel storage tanks using culture- and qPCR-based approaches
(2016)
Microbial contamination of fuels, associated with a wide variety of bacteria and fungi, leads to decreased product quality and can compromise equipment performance by biofouling and microbiologically influenced corrosion of pipelines and storage tanks. Detection and quantification of biomass are critical in monitoring fuel systems for an early detection of microbial outbreaks. The aims of this study are (i) to quantify bacterial and fungal contamination in samples from diesel storage tanks of petrol stations, using both culture dependent- and culture independent (qPCR) approaches, and (ii) to analyse the diversity of cultivable diesel-contaminating microorganisms with the purpose to create a strain collection for further use in biodeterioration experiments. Both methodological approaches revealed a high microbial contamination in all studied samples, with the bacterial load being much higher than the fungal load. The diversity of cultivable microorganisms was rather low. Based on criteria of abundance and fuel degradation potential, the most relevant microorganisms were identified as bacteria of genera Bacillus, Citrobacter, Burkholderia and Acetobacter, the filamentous fungi Paecilomyces variotii and Pseudallescheria boydii, and a Dipodascaceae yeast. Furthermore the validity and utility of qPCR-based methods are discussed.