physical-isolation-endospores-from-environmental-samples-targeted

Physical Isolation of Endospores from Environmental Samples by Targeted Lysis of Vegetative Cells

Endospore formation is a survival strategy found among some bacteria from the phylum Firmicutes. During endospore formation, these bacteria enter a ...

University of Neuchatel

Bacterial endospores are highly specialized cellular forms that allow endospore-forming Firmicutes (EFF) to tolerate harsh environmental conditions. EFF are considered ubiquitous in natural environments, in particular, those subjected to stress conditions. In addition to natural habitats, EFF are often the cause of contamination problems in anthropogenic environments, such as industrial production plants or hospitals. It is therefore desirable to assess their prevalence in environmental and industrial fields. To this end, a high-sensitivity detection method is still needed. The aim of this study was to develop and evaluate an approach based on quantitative PCR (qPCR). For this, the suitability of functional genes specific for and common to all EFF were evaluated. Seven genes were considered, but only spo0A was retained to identify conserved regions for qPCR primer design. An approach based on multivariate analysis was developed for primer design. Two primer sets were obtained and evaluated with 16 pure cultures, including representatives of the genera Bacillus, Paenibacillus, Brevibacillus, Geobacillus, Alicyclobacillus, Sulfobacillus, Clostridium, and Desulfotomaculum, as well as with environmental samples. The primer sets developed gave a reliable quantification when tested on laboratory strains, with the exception of Sulfobacillus and Desulfotomaculum. A test using sediment samples with a diverse EFF community also gave a reliable quantification compared to 16S rRNA gene pyrosequencing. A detection limit of about 10(4) cells (or spores) per gram of initial material was calculated, indicating this method has a promising potential for the detection of EFF over a wide range of applications.

Quantification of endospore-forming firmicutes by quantitative PCR with the functional gene spo0A.

In this study, we developed and validated a culture-independent method for diversity surveys to specifically detect endospore-forming Firmicutes. The global transcription regulator of sporulation (spo0A) was identified as a gene marker for endospore-forming Firmicutes. To enable phylogenetic classification, we designed a set of primers amplifying a 602 bp fragment of spo0A that we evaluated in pure cultures and environmental samples. The amplification was positive for 35 strains from 11 genera, yet negative for strains from Alicyclobacillus and Sulfobacillus. We also evaluated various DNA extraction methods because endospores often result in reduced yields. Our results demonstrate that procedures utilizing increased physical force improve DNA extraction. An optimized DNA extraction method on biomass pre-extracted from the environmental sample source (indirect DNA extraction) followed by amplification with the aforementioned primers for spo0A was then tested in sediments from two different sources. Specifically, we validated our culture-independent diversity survey methodology on a set of 8338 environmental spo0A sequences obtained from the sediments of Lakes Geneva (Switzerland) and Baikal (Russia). The phylogenetic affiliation of the environmental sequences revealed a substantial number of new clades within endospore-formers. This novel culture-independent approach provides a significant experimental improvement that enables exploration of the diversity of endospore-forming Firmicutes.

Stage 0 sporulation gene A as a molecular marker to study diversity of endospore-forming Firmicutes.

We present a method for the physical isolation of endospores from environmental samples allowing the specific targeting of endospore-forming bacteria for sequencing (endospore-enriched community). The efficiency of the method was tested on lake sediment samples. After 16S rRNA gene amplicon sequencing, the composition in the endospore-enriched community was compared with the community from untreated control samples (whole community). In the whole community, Firmicutes had a relative abundance of 8% and 19% in the two different lake sediments. In contrast, in the endospore-enriched community, Firmicutes abundance increased to 90.6% and 83.9%, respectively, confirming the efficiency of the endospore enrichment. The relative abundance of other microbial groups that form spore-like resisting states (i.e. actinobacteria, cyanobacteria and myxococcales) was below 2% in the endospore-enriched community, indicating that the method is adapted to true endospores. Representatives from two out of the three known classes of Firmicutes (Bacilli and Clostridia) were detected and supposedly asporogenic groups (e.g. Ethanoligenes and Trichococcus) could be detected. The method presented here is a leap forward for ecological studies of endospore-forming Firmicutes. It can be applied to other types of samples in order to reveal the diversity and metabolic potential of this bacterial group in the environment.

Endospore-enriched sequencing approach reveals unprecedented diversity of Firmicutes in sediments.

Anoxybacillus geothermalis strain GSsed3 is an endospore-forming thermophilic bacterium isolated from filter deposits in a geothermal site. This novel species has a larger genome size (7.2 Mb) than that of any other Anoxybacillus species, and it possesses genes that support its phenotypic metabolic characterization and suggest an intriguing link to metals.

Genome Sequence of Anoxybacillus geothermalis Strain GSsed3, a Novel Thermophilic Endospore-Forming Species.

The genome of strain GS3372 is the first publicly available strain of Aeribacillus pallidus. This endospore-forming thermophilic strain was isolated from a deep geothermal reservoir. The availability of this genome can contribute to the clarification of the taxonomy of the closely related Anoxybacillus, Geobacillus, and Aeribacillus genera.

Genome Sequence of Aeribacillus pallidus Strain GS3372, an Endospore-Forming Bacterium Isolated in a Deep Geothermal Reservoir.

Bacillus alveayuensis strain 24KAM51 was isolated from a marine hydrothermal vent in Milos, Greece. Its genome depicts interesting features of halotolerance and resistance to heavy metals.

Article	Year
Quantification of endospore-forming firmicutes by quantitative PCR with the functional gene spo0A. Applied and environmental microbiology\| PubMed ID: 23811505	2013
Stage 0 sporulation gene A as a molecular marker to study diversity of endospore-forming Firmicutes. Environmental microbiology reports\| PubMed ID: 24249300	2013
Endospore-enriched sequencing approach reveals unprecedented diversity of Firmicutes in sediments. Environmental microbiology reports\| PubMed ID: 25756117	2014
Genome Sequence of Anoxybacillus geothermalis Strain GSsed3, a Novel Thermophilic Endospore-Forming Species. Genome announcements\| PubMed ID: 26067952	2015
Genome Sequence of Aeribacillus pallidus Strain GS3372, an Endospore-Forming Bacterium Isolated in a Deep Geothermal Reservoir. Genome announcements\| PubMed ID: 26316637	2015
Genome Sequence of Bacillus alveayuensis Strain 24KAM51, a Halotolerant Thermophile Isolated from a Hydrothermal Vent. Genome announcements\| PubMed ID: 26316638	2015

Nicole Jeanneret

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