Oligotrophic bacteria from rendzina forest soil

Identifying Hidden Viable Bacterial Taxa in Tropical Forest Soils Using Amplicon Sequencing of Enrichment Cultures

Simple Summary

The study of a microbial community nowadays mostly relies on environmental DNA (eDNA)-based amplicon sequencing. However, some studies report that this method is not able to capture all bacterial taxa in the community. This study presents an enrichment culture-based amplicon sequencing method to estimate the proportion of culturable bacteria in soil. A bacterial community derived from this method was compared with those derived from culture-independent methods (eDNA-based amplicon sequencing). This study revealed that the majority of cultured bacteria were rare or completely absent in the community detected by the culture-independent method. Nevertheless, the dominant bacterial Operational Taxonomic Units (OTUs) were also observed, as 8 out of the 30 most frequently detected bacteria from eDNA were found in the enrichment cultures. The method proposed in this study could extend bacterial community’s information derived from the culture-independent method. Furthermore, the enrichment culture-based amplicon sequencing method could be a promising tool for quick screening of a culturable bacterial community and its associated function for various applications.

Abstract

This study aims to estimate the proportion and diversity of soil bacteria derived from eDNA-based and culture-based methods. Specifically, we used Illumina Miseq to sequence and characterize the bacterial communities from (i) DNA extracted directly from forest soil and (ii) DNA extracted from a mixture of bacterial colonies obtained by enrichment cultures on agar plates of the same forest soil samples. The amplicon sequencing of enrichment cultures allowed us to rapidly screen a culturable community in an environmental sample. In comparison with an eDNA community (based on a 97% sequence similarity threshold), the fact that enrichment cultures could capture both rare and abundant bacterial taxa in forest soil samples was demonstrated. Enrichment culture and eDNA communities shared 2% of OTUs detected in total community, whereas 88% of enrichment cultures community (15% of total community) could not be detected by eDNA. The enrichment culture-based methods observed 17% of the bacteria in total community. FAPROTAX functional prediction showed that the rare and unique taxa, which were detected with the enrichment cultures, have potential to perform important functions in soil systems. We suggest that enrichment culture-based amplicon sequencing could be a beneficial approach to evaluate a cultured bacterial community. Combining this approach together with the eDNA method could provide more comprehensive information of a bacterial community. We expected that more unique cultured taxa could be detected if further studies used both selective and non-selective culture media to enrich bacteria at the first step.

Chromatin binding of FOXA1 is promoted by LSD1-mediated demethylation in prostate cancer

FOXA1 functions as a pioneer transcription factor by facilitating the access to chromatin for steroid hormone receptors, such as androgen receptor and estrogen receptor^1-4, but mechanisms regulating its binding to chromatin remain elusive. LSD1 (KDM1A) acts as a transcriptional repressor by demethylating mono/dimethylated histone H3 lysine 4 (H3K4me1/2)^5,6, but also acts as a steroid hormone receptor coactivator through mechanisms that are unclear. Here we show, in prostate cancer cells, that LSD1 associates with FOXA1 and active enhancer markers, and that LSD1 inhibition globally disrupts FOXA1 chromatin binding. Mechanistically, we demonstrate that LSD1 positively regulates FOXA1 binding by demethylating lysine 270, adjacent to the wing2 region of the FOXA1 DNA-binding domain. Acting through FOXA1, LSD1 inhibition broadly disrupted androgen-receptor binding and its transcriptional output, and dramatically decreased prostate cancer growth alone and in synergy with androgen-receptor antagonist treatment in vivo. These mechanistic insights suggest new therapeutic strategies in steroid-driven cancers.

Cultivation-success of rare soil bacteria is not influenced by incubation time and growth medium

Rare bacterial species have recently attracted interest due to their many potential beneficial functions. However, only little is known about their cultivability. In this study we test the hypotheses that the use of flow cell-sorting for cultivation results in a high proportion of rare soil bacterial isolates relative to bacterial taxa that are abundant in soil. Moreover, we investigate whether different oligotrophic cultivation media and a prolonged incubation time increase the number of cultivated rare species. In a cultivation study we used flow cell sorting to select for small cells and to separate single cells, and grew bacteria on different oligotrophic media with prolonged incubation times. The abundance of the isolates in the field was assessed by comparing them to a 454-sequencing dataset from the same soil. Consequentially, all bacterial isolates were classified as either rare (<0.01% relative abundance) or abundant (>0.01% relative abundance) in the field soil. We found more bacterial taxa among the isolates that were abundant in soil than would be expected by the proportion of abundant species in the field. Neither incubation time nor growth medium had an influence on the recovery of rare species. However, we did find differences in time until visible growth on the plate between different phylogenetic classes of the isolates. These results indicate that rare cultivable species are active and not more likely to be dormant than abundant species, as has been suggested as a reason for their rarity. Moreover, future studies should be aware of the influence incubation time might have on the phylogenetic composition of the isolate collection.

The use of metagenomic approaches to analyze changes in microbial communities

Microbes are the most abundant biological entities found in the biosphere. Identification and measurement of microorganisms (including viruses, bacteria, archaea, fungi, and protists) in the biosphere cannot be readily achieved due to limitations in culturing methods. A non-culture based approach, called “metagenomics”, was developed that enabled researchers to comprehensively analyse microbial communities in different ecosystems. In this study, we highlight recent advances in the field of metagenomics for analyzing microbial communities in different ecosystems ranging from oceans to the human microbiome. Developments in several bioinformatics approaches are also discussed in context of microbial metagenomics that include taxonomic systems, sequence databases, and sequence-alignment tools. In summary, we provide a snapshot for the recent advances in metagenomics approach for analyzing changes in the microbial communities in different ecosystems.

Isolation and partial characterization of bacterial strains on low organic carbon medium from soils fertilized with different organic amendments

A total of 720 bacterial strains were isolated from soils with four different organic amendment regimes on a low organic carbon (low-C) agar medium (10 µg C ml(-1)) traditionally used for isolation of oligotrophs. Organic amendments in combination with field history resulted in differences in dissolved organic carbon contents in these soils. There were negative correlations between total and dissolved organic carbon content and the number of isolates on low-C agar medium, whereas these correlations were absent for bacterial strains isolated from the same soil on high-C agar medium (1,000 µg C ml(-1)). Repeated transfers (up to ten times) of the isolates from low-C agar medium to fresh low- and high-C agar media were done to test for exclusive growth under oligotrophic conditions. The number of isolates exclusively growing under oligotrophic conditions dropped after each subsequent transfer from 241 after the first to 98 after the third transfer step. Identification on the basis of partial 16S rRNA gene sequences revealed that most of the 241 isolates (as well as the subset of 98 isolates) belong to widespread genera such as Streptomyces, Rhizobium, Bradyrhizobium, and Mesorhizobium, and the taxonomic composition of dominant genera changed from the first transfer step to the third. A selected subset of 17 isolates were further identified and characterized for exclusive growth on low-C agar medium. Two isolates continued to grow only on low-C agar medium up to the tenth transfer step and matched most closely with Rhizobium sullae and an uncultured bacterium on the basis of the almost full-length 16S rRNA gene. It was concluded that the vast majority of strains which are isolated on low-C agar media belong to the trophic group of microorganisms adapted to a "broad range" of carbon concentrations, including well-known and widespread bacterial genera. Oligotrophy is a physiological, not a taxonomic property, and can only be identified by cultural means so far. We showed that true oligotrophs that are unable to grow on high carbon media are rare and belong to genera that also contain broad-range and copiotrophic strains.

Metagenomics: application of genomics to uncultured microorganisms

Metagenomics (also referred to as environmental and community genomics) is the genomic analysis of microorganisms by direct extraction and cloning of DNA from an assemblage of microorganisms. The development of metagenomics stemmed from the ineluctable evidence that as-yet-uncultured microorganisms represent the vast majority of organisms in most environments on earth. This evidence was derived from analyses of 16S rRNA gene sequences amplified directly from the environment, an approach that avoided the bias imposed by culturing and led to the discovery of vast new lineages of microbial life. Although the portrait of the microbial world was revolutionized by analysis of 16S rRNA genes, such studies yielded only a phylogenetic description of community membership, providing little insight into the genetics, physiology, and biochemistry of the members. Metagenomics provides a second tier of technical innovation that facilitates study of the physiology and ecology of environmental microorganisms. Novel genes and gene products discovered through metagenomics include the first bacteriorhodopsin of bacterial origin; novel small molecules with antimicrobial activity; and new members of families of known proteins, such as an Na(+)(Li(+))/H(+) antiporter, RecA, DNA polymerase, and antibiotic resistance determinants. Reassembly of multiple genomes has provided insight into energy and nutrient cycling within the community, genome structure, gene function, population genetics and microheterogeneity, and lateral gene transfer among members of an uncultured community. The application of metagenomic sequence information will facilitate the design of better culturing strategies to link genomic analysis with pure culture studies.

Sphingomonas oligophenolica sp. nov., a halo- and organo-sensitive oligotrophic bacterium from paddy soil that degrades phenolic acids at low concentrations

The taxonomic position of a halo- and organo-sensitive, oligotrophic soil bacterium, strain S213T, was investigated. Cells were Gram-negative, non-motile, strictly aerobic, yellow-pigmented rods of short to medium length on diluted nutrient broth. When 0·1–0·4 % (w/v) NaCl was added to diluted media composed of peptone and meat extract, growth was inhibited with increasing NaCl concentration and the cells became long aberrant forms. When 6 mM CaCl2 was added, the cells grew quite normally and aberrant cells were no longer found at 0·1–0·5 % (w/v) NaCl. Chemotaxonomically, strain S213T contains chemical markers that indicate its assignment to the Sphingomonadaceae: the presence of ubiquinone Q-10 as the predominant respiratory quinone, C18 : 1 and C16 : 0 as major fatty acids, C14 : 0 2-OH as the major 2-hydroxy fatty acid and sphingoglycolipids. 16S rRNA gene sequence analysis indicated that strain S213T belongs to the genus Sphingomonas, exhibiting high sequence similarity to the 16S rRNA gene sequences of Sphingomonas mali IFO 15500T (98·3 %), Sphingomonas pruni IFO 15498T (98·0 %), Sphingomonas asaccharolytica IFO 15499T (97·9 %) and Sphingomonas echinoides DSM 1805T (97·8 %). The results of DNA–DNA hybridization experiments and its phenotypic characteristics clearly distinguished the strain from its nearest neighbours and demonstrate that strain S213T represents a novel Sphingomonas species, for which the name Sphingomonas oligophenolica sp. nov. is proposed. The type strain is S213T (=JCM 12082T=CIP 107926T).

Soil microbial community of abandoned sand fields

Microbiological evaluation of sandy grassland soils from two different stages of secondary succession on abandoned fields (4 and 8 years old fallow) was carried out as a part of research focused on restoration of semi-natural vegetation communities in Kiskunság National Park in Hungary. There was an apparent total N and organic C enrichment, stimulation of microbial growth and microbial community structure change on fields abandoned by agricultural practice (small family farm) in comparison with native undisturbed grassland. A successional trend of the microbial community was found after 4 and 8 years of fallow-lying soil. It consisted in a shift of r-survival strategy to more efficient C economy, in a decrease of specific respiration and metabolic activity, forced accumulation of storage bacterial compounds and increased fungal distribution. The composition of microbial phospholipid fatty acids mixture of soils abandoned at various times was significantly different.

Oligophilic bacteria as tools to monitor aseptic pharmaceutical production units

The bacterial loads of air, surfaces, and personnel in clean rooms are routinely monitored using a set of standard media. Bacteria that can grow on these media are a tiny fraction of the total numbers in any environment. A substantial proportion of bacteria long thought to be unculturable were recently shown to be oligophilic. Oligophile counts in clean rooms in our studies exceeded the standard plate counts by up to 2 orders of magnitude. They responded to disinfection routines in ways similar to the responses of conventional bacteria. We suggest that oligophiles are better tools than conventional bacteria for environmental monitoring in aseptic pharmaceutical production units.

Effect of Metal-Rich Sludge Amendments on the Soil Microbial Community

The effects of heavy-metal-containing sewage sludge on the soil microbial community were studied in two agricultural soils of different textures, which had been contaminated separately with three predominantly single metals (Cu, Zn, and Ni) at two different levels more than 20 years ago. We compared three community-based microbiological measurements, namely, phospholipid fatty acid (PLFA) analysis to reveal changes in species composition, the Biolog system to indicate metabolic fingerprints of microbial communities, and the thymidine incorporation technique to measure bacterial community tolerance. In the Luddington soil, bacterial community tolerance increased in all metal treatments compared to an unpolluted-sludge-treated control soil. Community tolerance to specific metals increased the most when the same metal was added to the soil; for example, tolerance to Cu increased most in Cu-polluted treatments. A dose-response effect was also evident. There were also indications of cotolerance to metals whose concentration had not been elevated by the sludge treatment. The PLFA pattern changed in all metal treatments, but the interpretation was complicated by the soil moisture content, which also affected the results. The Biolog measurements indicated similar effects of metals and moisture to the PLFA measurements, but due to high variation between replicates, no significant differences compared to the uncontaminated control were found. In the Lee Valley soil, significant increases in community tolerance were found for the high levels of Cu and Zn, while the PLFA pattern was significantly altered for the soils with high levels of Cu, Ni, and Zn. No effects on the Biolog measurements were found in this soil.

Na+-induced structural change of a soil bacterium, S34, and Ca2+ requirement for preserving its original structure

A drastic change in the outer membrane structure of a salt-sensitive soil bacterium, S34, related to the genus Deinococcus was induced by 0.2 to 0.4% (wt/vol) NaCl. The change was relieved by 6 mM CaCl2 and induced by 1 mM EGTA. The results indicate the strong dependence of the organism on calcium.

Assessment of survival during starvation of Escherichia coli and Klebsiella pneumoniae in artificial urine: analysis of the kinetics of colony formation

A kinetic model of colony formation was proposed by Hattori, based on a count of the colonies that appear on a plate in successive short intervals of time. In this model, three parameters (lambda, tr and N infinity) are defined, which reflect the ability of a bacterium to yield colonies and allow us to described the dynamics of bacterial populations in soil and of E. coli at different growth phases. In this paper we report a reparametrization of the kinetic model of colony formation, with the aim of facilitating more accurate calculation of lambda and tr. Moreover, we observed that during the starvation of E. coli and K. pneumoniae in urine, lambda can be used to assess survival, since this parameter clearly decreases during starvation. Retardation time values (tr) were similar in E. coli and K. pneumoniae throughout the starvation experimental period.

Physiological bases of oligotrophy of microorganisms and the concept of microbial community

Three groups of physiological processes in microorganisms are considered the physiological basis of oligotrophy: the greater substrate affinity of the oligotrophs' transport systems, efficient or "economical" metabolism, and existence of a "master reaction" or "rate-determining steps" controlling the rate of metabolism. Heterotrophic microorganisms are divided into three unequal groups according to "reaction norma." Two groups representing the extremes are small groups with the "narrow" reaction norma, regarding the concentrations and structure of the assimilated organic compounds and variability limits of the physiological characteristics mentioned above. The third, intermediate group includes the majority of microorganisms with the "wide" reaction norma.