Kin discrimination, broadly defined as differential treatment of conspecifics according to their relatedness, could help biological systems direct cooperative behavior toward their relatives. Here we ...investigated the ability of the soil bacterium Bacillus subtilis to discriminate kin from nonkin in the context of swarming, a cooperative multicellular behavior. We tested a collection of sympatric conspecifics from soil in pairwise combinations and found that despite their history of coexistence, the vast majority formed distinct boundaries when the swarms met. Some swarms did merge, and most interestingly, this behavior was only seen in the most highly related strain pairs. Overall the swarm interaction phenotype strongly correlated with phylogenetic relatedness, indicative of kin discrimination. Using a subset of strains, we examined cocolonization patterns on plant roots. Pairs of kin strains were able to cocolonize roots and formed a mixed-strain biofilm. In contrast, inoculating roots with pairs of nonkin strains resulted in biofilms consisting primarily of one strain, suggestive of an antagonistic interaction among nonkin strains. This study firmly establishes kin discrimination in a bacterial multicellular setting and suggests its potential effect on ecological interactions.
The occurrence and environmental toxicity of pharmaceuticals have recently attracted increasing attention. Diclofenac is a highly consumed non-steroidal anti-inflammatory drug, which is often ...detected in wastewaters, but investigations of its influence on bacteria are scarce.
We investigated the influence of this pharmaceutical on bacterial community in activated sludge exposed to increasing concentrations of diclofenac in fed-batch reactors over 41 days. Nitrification activity of the activated sludge was measured and changes in bacterial community structure were followed using culture-independent molecular method (terminal restriction fragment length polymorphism, T-RFLP) and by the cultivation approach.
Nitrification activity was not detectably influenced by the addition of diclofenac, while the main change of the bacterial community structure was detected only at the end of incubation (after 41 days) when diclofenac was added to artificial wastewater as the only carbon source. Changes in community composition due to enrichment were observed using cultivation approach. However, taxonomic affiliation of isolates did not match taxons identified by T-RFLP community profiling. Isolates obtained from activated sludge used as inoculum belonged to five genera:
,
,
r,
and
, known for their potential to degrade aromatic compounds. However, only
species were isolated after the last enrichment step on minimal agar plates with diclofenac added as the sole carbon source.
Our results suggest that the selected recalcitrant and commonly detected pharmaceutical does not strongly influence the sensitive and important nitrification process of wastewater treatment. Moreover, the isolated strains obtained after enrichment procedure that were able to grow on minimal agar plates with diclofenac added as the only carbon source could serve as potential model bacteria to study bacterial diclofenac degradation.
Multicellularity inherently involves a number of cooperative behaviors that are potentially susceptible to exploitation but can be protected by mechanisms such as kin discrimination. Discrimination ...of kin from non-kin has been observed in swarms of the bacterium Bacillus subtilis, but the underlying molecular mechanism has been unknown. We used genetic, transcriptomic, and bioinformatic analyses to uncover kin recognition factors in this organism. Our results identified many molecules involved in cell-surface modification and antimicrobial production and response. These genes varied significantly in expression level and mutation phenotype among B. subtilis strains, suggesting interstrain variation in the exact kin discrimination mechanism used. Genome analyses revealed a substantial diversity of antimicrobial genes present in unique combinations in different strains, with many likely acquired by horizontal gene transfer. The dynamic combinatorial effect derived from this plethora of kin discrimination genes creates a tight relatedness cutoff for cooperation that has likely led to rapid diversification within the species. Our data suggest that genes likely originally selected for competitive purposes also generate preferential interactions among kin, thus stabilizing multicellular lifestyles.
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•Kin discrimination (KD) in B. subtilis leads to cell death and stress response•Various genes are used for KD, generally antimicrobials and cell-surface modifiers•Transcription of KD genes varies extensively, especially when encountering non-kin•KD genes are poorly conserved, often absent even in the most closely related strains
Lyons et al. show that B. subtilis cells use a collection of intercellular attack and defense molecules to discriminate kin from non-kin—only those cells that contain the right set of immunities will survive and be treated as kin. These kin discrimination genes are numerous and vary greatly between strains in both conservation and expression levels.
We investigated microbial growth in increasing concentrations of hexavalent chromium (Cr(VI)) and its reduction by a microbial community enriched from tannery effluent and by the bacterial strains ...isolated from the enriched community. The bacterial growth was monitored by measuring the optical cell density (OD
), while the Cr(VI) concentration in the samples was determined using spectrophotometry and liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). At a Cr(VI) concentration of 100 mg/L, the isolates affiliated with Pseudomonas aeruginosa (P. aeruginosa) reached higher optical cell densities, but were in general less effective for Cr(VI) reduction than the isolates affiliated with Mammaliicoccus sciuri (M. sciuri). All three M. sciuri isolates and only one of the seven P. aeruginosa isolates were able to reduce 50% of the Cr(VI) with an initial concentration of 100 mg/L within 24 h (pH 7.1), while the six isolates affiliated with P. aeruginosa were less effective. Compared to the isolated, individual bacterial strains, the enriched microbial community was better adapted to the elevated Cr(VI) concentrations, but needed a longer time (48 h) to reduce the Cr(VI) with the same efficacy as the most efficient individual isolates. The ability of the enriched microbial community and the isolated bacterial strains to reduce the Cr(VI) highlights their potential for use in the rapid bioremediation of wastewaters contaminated with Cr(VI).
Abstract
Bacillus subtilis
is a soil bacterium that is competent for natural transformation. Genetically distinct
B. subtilis
swarms form a boundary upon encounter, resulting in killing of one of the ...strains. This process is mediated by a fast-evolving kin discrimination (KD) system consisting of cellular attack and defence mechanisms. Here, we show that these swarm antagonisms promote transformation-mediated horizontal gene transfer between strains of low relatedness. Gene transfer between interacting non-kin strains is largely unidirectional, from killed cells of the donor strain to surviving cells of the recipient strain. It is associated with activation of a stress response mediated by sigma factor SigW in the donor cells, and induction of competence in the recipient strain. More closely related strains, which in theory would experience more efficient recombination due to increased sequence homology, do not upregulate transformation upon encounter. This result indicates that social interactions can override mechanistic barriers to horizontal gene transfer. We hypothesize that KD-mediated competence in response to the encounter of distinct neighbouring strains could maximize the probability of efficient incorporation of novel alleles and genes that have proved to function in a genomically and ecologically similar context.
Ammonium removal is a key step in biological wastewater treatment and novel approaches that improve this process are in great demand. The aim of this study is to test the hypothesis that ammonium ...removal from wastewater can be stimulated by static magnetic fields. This was achieved by analysis of the effects of static magnetic field (SMF) on the growth and activity of
, a key ammonia-oxidising bacterium, where increased growth and increased ammonia oxidation rate were detected when bacteria were exposed to SMF at 17 mT. Additionally, the effect of SMF on mixed cultures of ammonia oxidisers in activated sludge, incubated in sequencing batch bioreactors simulating wastewater treatment process, was assessed. SMFs of 30 and 50 mT, but not of 10 mT, increased ammonium oxidation rate in municipal wastewater by up to 77% and stimulated ammonia oxidiser growth. The results demonstrate the potential for use of static magnetic fields in increasing ammonium removal rates in biological wastewater treatment plants.
Pozadina istraživanja. U zadnje vrijeme prisutnost i toksičnost farmaceutskih proizvoda u okolišu pobuđuju veliki interes javnosti. Diklofenak je nesteroidni protuupalni lijek koji se uvelike ...koristi, pa često dospijeva u otpadne vode, no usprkos tome postoji vrlo malo istraživanja o njegovom utjecaju na bakterije aktivnog mulja. Eksperimentalni pristup. Ispitali smo utjecaj ovog lijeka na bakterijsku populaciju aktivnog mulja u reaktoru s pritokom supstrata kojem smo dodavali diklofenak tijekom 41 dana. Izmjerena je nitrifikacijska aktivnost bakterija aktivnog mulja, a promjena sastava bakterijske populacije praćena je molekularnom metodom za izravnu identifikaciju (T-RFLP) te uzgojem bakterija. Rezultati i zaključci. Dodatak diklofenaka nije vidljivo utjecao na nitrifikacijsku aktivnost bakterija, a veća je promjena sastava bakterijske populacije opažena tek na kraju inkubacije (nakon 41 dana), kad je diklofenak bio dodan kao jedini izvor ugljika u otopinu koja simulira sastav otpadnih voda. Promjene sastava bakterijske populacije nakon obogaćivanja podloge diklofenakom primijećene su nakon izolacije i praćenja rasta bakterija na minimalnoj podlozi. Međutim, taksonomska pripadnost izolata nije odgovarala taksonima identificiranim metodom T-RFLP. Izolati dobiveni iz aktivnog mulja te korišteni kao inokulum spadali su u pet rodova bakterija: Comamonas, Arthrobacter, Acinetobacter, Citrobacter i Aeromonas, koje su poznate po sposobnosti razgradnje aromatskih spojeva. Međutim, nakon posljednjeg dodatka diklofenaka kao jedinog izvora ugljika minimalnoj podlozi izolirane su jedino bakterije vrste Pseudomonas. Novina i znanstveni doprinos. Rezultati pokazuju da ispitani lijek, koji ima ograničenu biorazgradivost a često ga nalazimo u otpadnim vodama, ne utječe u velikoj mjeri na osjetljiv i bitan postupak nitrifikacije otpadnih voda. Osim toga, zaključeno je da izolirani sojevi bakterija koji su rasli na minimalnoj podlozi s diklofenakom kao jedinim izvorom ugljika mogu poslužiti kao model za proučavanje bakterijske razgradnje diklofenaka.
Many peatlands in Europe have been subjected to land reclamation and systematic drainage, which have substantially affected nutrient cycles in the soil. This work reviews published studies on ...microbial processes linked to carbon and nitrogen transformations in the soils of the Ljubljana marsh, a drained peatland positioned close to Ljubljana, the capital of Slovenia. This region is known for its dramatic diversity of animal and plant life, but below ground it hides diverse bacterial and archaeal communities that are highly responsive to environmental changes and make the Ljubljana marsh soils a good source of N.sub.2O and CO.sub.2, and a sink for CH.sub.4. Methanogenesis is highly restricted in these soils due to competition for electron donors with iron reducers. In addition, methane is efficiently removed by methanotrophs, which are highly active, especially in the soil layers exposed to the changing water table. Denitrification is limited by electron acceptors and in deeper soil layers also by carbon, which becomes more recalcitrant with depth. Nitrification involves bacterial and archaeal ammonia oxidisers with ammonia oxidation rates being among the highest in the world. Interestingly, ammonia-oxidising Thaumarchaeota in acidic bog soils thrive only on ammonia released through mineralisation of organic matter and are incapable of oxidising added mineral ammonia. The soils of the Ljubljana marsh are rich in bacterial laccase-like genes, which may encode enzymes involved in lignin degradation and are therefore interesting for bioexploitations. Future challenges involve designing studies that will reveal specific physiological functions of phenol oxidases and other enzymes involved in peat transformations and address relations between microbial diversity, function and ecosystem responses to anthropogenic disturbances. Key words: microbial community, microbial diversity, peatland, greenhouse gas, nitrification, denitrification, methanogenesis, methanotrophy, laccase, amoA
Swarming is the collective movement of bacteria across a surface. It requires the production of surfactants (public goods) to overcome surface tension and provides an excellent model to investigate ...bacterial cooperation. Previously, we correlated swarm interaction phenotypes with kin discrimination between B. subtilis soil isolates, by showing that less related strains form boundaries between swarms and highly related strains merge. However, how kin discrimination affects cooperation and territoriality in swarming bacteria remains little explored. Here we show that the pattern of surface colonization by swarming mixtures is influenced by kin types. Closely related strain mixtures colonize the surface in a mixed swarm, while mixtures of less related strains show competitive exclusion as only one strain colonizes the surface. The outcome of nonkin swarm expansion depends on the initial ratio of the competing strains, indicating positive frequency-dependent competition. We find that addition of surfactin (a public good excreted from cells) can complement the swarming defect of nonkin mutants, whereas close encounters in nonkin mixtures lead to territorial exclusion, which limits the exploitation of surfactin by nonkin nonproducers. The work suggests that kin discrimination driven competitive territorial exclusion may be an important determinant for the success of cooperative surface colonization.
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