Environmental microbiology最新文献

Ammonia-oxidising archaea (AOA) are important microorganisms contributing towards the nitrogen flux in the environment. Unlike archaea from other major phyla, genetic tools are yet to be developed for the AOA, and identification of antibiotic resistance markers for selecting mutants is required for a genetic system. The aim of this study was to test the effects of selected antibiotics (hygromycin B, neomycin, apramycin, puromycin, novobiocin) on pure cultures of three well studied AOA strains, ‘Candidatus Nitrosocosmicus franklandianus C13’, Nitrososphaera viennensis EN76 and Nitrosopumilus maritimus SCM1. Puromycin, hygromycin B and neomycin inhibited some but not all tested archaeal strains. All strains were resistant to apramycin and inhibited by novobiocin to various degrees. As N. viennensis EN76 was relatively more resistant to the tested antibiotics, a wider range of concentrations and compounds (chloramphenicol, trimethoprim, statins) was tested against this strain. N. viennensis EN76 was inhibited by trimethoprim, but not by chloramphenicol, and growth recovered within days in the presence of simvastatin, suggesting either degradation of, or spontaneous resistance against, this compound. This study highlights the physiological differences between different genera of AOA and has identified new candidate antibiotics for selective enrichment and the development of selectable markers for genetic systems in AOA.

We examined the effects of symbiont identity and heat stress on the host metabolome and proteome in the cnidarian–dinoflagellate symbiosis. Exaiptasia diaphana (‘Aiptasia’) was inoculated with its homologous (i.e., native) symbiont Breviolum minutum or a heterologous (i.e., non-native) symbiont (Symbiodinium microadriaticum; Durusdinium trenchii) and thermally stressed. Integrated metabolome and proteome analyses characterised host thermal responses between symbioses, with clear evidence of enhanced nutritional deprivation and cellular stress in hosts harbouring heterologous symbionts following temperature stress. Host metabolomes were partially distinct at the control temperature; however, thermal stress caused metabolomes of anemones containing the two heterologous symbionts to become more alike and more distinct from those containing B. minutum. While these patterns could be partly explained by innate symbiont-specific differences, they may also reflect differences in symbiont density, as under control conditions D. trenchii attained 60% and S. microadriaticum 15% of the density attained by B. minutum, and at elevated temperature only D. trenchii–colonised anemones bleached (60% loss). Our findings add to a growing literature that highlights the physiological limits of partner switching as a means of adaptation to global warming. However, we also provide tentative evidence for improved metabolic functioning with a heterologous symbiont (D. trenchii) after sustained symbiosis.

Dinoflagellates of the family Symbiodiniaceae are important symbionts of diverse marine animals and they also occupy different environmental niches on coral reefs. The link between diversity at ecosystem-scale to microhabitats of Symbiodiniaceae within the coral holobiont is largely unknown. Using ITS2-amplicon sequencing, we compared Symbiodiniaceae communities across four environments (seawater, near-reef vs. distant sediments and turf algae) and two coral microhabitats (tissue, mucus) on a coral reef in the Red Sea. We found that coral and environmental habitats were both dominated by the genera Symbiodinium, Cladocopium and Durusdinium, but environmental habitats additionally harboured Fugacium, Gerakladium and Halluxium. Each environmental habitat harboured a distinct Symbiodiniaceae community. Nonetheless, 17 ITS2 sequences were shared among coral and environmental habitats and were also part of nearly half of the ITS2 type profiles in coral-based communities. Tissues and mucus of 49 coral colonies from 17 genera had largely identical Symbiodiniaceae communities. Together with the large difference between environmental Symbiodiniaceae communities and those in the coral tissue and mucus, our results indicate a clear barrier between host-associated and environmental Symbiodiniaceae communities marked by only few shared complete type profiles. Monitoring coral colonies after mucus sampling confirmed its suitability for long-term monitoring of coral-associated Symbiodiniaceae communities.

Classical models from theoretical ecology are seeing increasing uptake in microbial ecology, but there remains rich potential for closer cross-pollination. Here we explore opportunities for stronger integration of ecological theory into microbial research (and vice versa) through the lens of so-called “modern” coexistence theory. Coexistence theory can be used to disentangle the contributions different mechanisms (e.g., resource partitioning, environmental variability) make to species coexistence. We begin with a short primer on the fundamental concepts of coexistence theory, with an emphasis on the relevance to microbial communities. We next present a systematic review, which highlights the paucity of empirical applications of coexistence theory in microbial systems. In light of this gap, we then identify and discuss ways in which: (i) coexistence theory can help to answer fundamental and applied questions in microbial ecology, particularly in spatio-temporally heterogeneous environments, and (ii) experimental microbial systems can be leveraged to validate and advance coexistence theory. Finally, we address several unique but often surmountable empirical challenges posed by microbial systems, as well as some conceptual limitations. Nevertheless, thoughtful integration of coexistence theory into microbial ecology presents a wealth of opportunities for the advancement of both theoretical and microbial ecology.

Some mat-forming cyanobacteria produce harmful cyanotoxins, yet benthic species remain understudied compared to planktonic counterparts. This study assesses the diversity, distribution and toxin production of mat-forming cyanobacteria across lentic and lotic systems in Nova Scotia, Canada. We documented greater cyanobacterial species richness in lentic environments, with six dominant species distributed into two major Microcoleus clades, five of which represent putative novel taxa. Two Microcoleus species with the genetic repertoire to produce anatoxins were prevalent. One has been previously reported in Canada, while the second represents a novel species found exclusively in an environment impacted by discharge from a water treatment plant. We observed variability in the gene clusters responsible for the biosynthesis of anatoxin-a and associated analogues (ATXs), including the discovery of a novel anaG variant with a ~ 1.7 kb insertion in a Microcoleus strain dominating homoanatoxin-producing mats. This extended anaG, encoding a polyketide synthase with an additional methyltransferase domain, coexists with shorter variants, leading to the production of a mixture of ATXs. These findings highlight the genetic diversity of benthic cyanobacteria in freshwater environments, with Microcoleus as the primary contributor to the production of ATXs in both lentic and lotic systems, underscoring their potential to produce harmful toxins.