A novel marine bacterium algicidal to the toxic dinoflagellate Alexandrium tamarense

Aims: This work is aiming at investigating algicidal characterization of a bacterium isolate DHQ25 against harmful alga Alexandrium tamarense. Methods and Results: 16S rDNA sequence analysis showed that the most probable affiliation of DHQ25 belongs to the γ‐proteobacteria subclass and the genus Vibrio. Bacterial isolate DHQ25 showed algicidal activity through an indirect attack. Xenic culture of A. tamarense was susceptible to the culture filtrate of DHQ25 by algicidal activity assay. Algicidal process demonstrated that the alga cell lysed and cellular substances released under the visual field of microscope. DHQ25 was a challenge controller of A. tamarense by the above characterizations of algicidal activity assay and algicidal process. Conclusion: Interactions between bacteria and harmful algal bloom (HAB) species proved to be an important factor regulating the population of these algae. Significance and Impact of Study: This is the first report of a Vibrio sp. bacterium algicidal to the toxic dinoflagellate A. tamarense. The findings increase our knowledge of the role of bacteria in algal–bacterial interaction.     

An invasive beetle–fungus complex is maintained by fungal nutritional-compensation mediated by bacterial volatiles

Mutualisms between symbiotic microbes and animals have been well documented, and nutritional relationships provide the foundation for maintaining beneficial associations. The well-studied mutualism between bark beetles and their fungi has become a classic model system in the study of symbioses. Despite the nutritional competition between bark beetles and beneficial fungi in the same niche due to poor nutritional feeding substrates, bark beetles still maintain mutualistic associations with beneficial fungi over time. The mechanism behind this phenomenon, however, remains largely unknown. Here, we demonstrated the bark beetle Dendroctonus valens LeConte relies on the symbiotic bacterial volatile ammonia, as a nitrogen source, to regulate carbohydrate metabolism of its mutualistic fungus Leptographium procerum to alleviate nutritional competition, thereby maintaining the stability of the bark beetle–fungus mutualism. Ammonia significantly reduces competition of L. procerum for carbon resources for D. valens larval growth and increases fungal growth. Using stable isotope analysis, we show the fungus breakdown of phloem starch into d-glucose by switching on amylase genes only in the presence of ammonia. Deletion of amylase genes interferes with the conversion of starch to glucose. The acceleration of carbohydrate consumption and the conversion of starch into glucose benefit this invasive beetle–fungus complex. The nutrient consumption–compensation strategy mediated by tripartite beetle–fungus–bacterium aids the maintenance of this invasive mutualism under limited nutritional conditions, exacerbating its invasiveness with this competitive nutritional edge.Subject terms: Microbial ecology, Microbial ecology     

Wheat Bran Enhances the Cytotoxicity of Immobilized Alcaligenes aquatilis F8 against Microcystis aeruginosa

Algicidal bacteria offer a promising option for killing cyanobacteria. Therefore, a new Alcaligenes aquatilis strain F8 was isolated to control Microcystis aeruginosa in this study. The algicidal activity of strain F8 was dependent on the cell density of M. aeruginosa, and the maximal algicidal rate of the free bacterium reached 88.45% within 72 h. With a view to its application to the control of M. aeruginosa in the natural environment, strain F8 was immobilized in sodium alginate beads, but immobilization of the strain decreased its algicidal rate compared to that of the free bacterium. However, addition of wheat bran to the sodium alginate matrix used to immobilize strain F8 not only eliminated the adverse effects of immobilization on the bacteria but also resulted in an 8.83% higher algicidal rate of the immobilized than free bacteria. Exclusion and recovery methods were used to identify key ingredients of wheat bran and gain insight into the mechanism underlying the observed enhancement of algicidal activity. This analysis indicated that certain factors in wheat bran, including vitamins B₁, B₂, B₉, and E were responsible for promoting bacterial growth and thereby improving the algicidal rate of immobilized strain F8. Our findings indicate that wheat bran is able to improve the algicidal efficiency of A. aquatilis strain F8 for killing M. aeruginosa and is a good source of not only carbon and nitrogen but also vitamins for bacteria.     

Stability of Microbiota Facilitated by Host Immune Regulation: Informing Probiotic Strategies to Manage Amphibian Disease

Microbial communities can augment host immune responses and probiotic therapies are under development to prevent or treat diseases of humans, crops, livestock, and wildlife including an emerging fungal disease of amphibians, chytridiomycosis. However, little is known about the stability of host-associated microbiota, or how the microbiota is structured by innate immune factors including antimicrobial peptides (AMPs) abundant in the skin secretions of many amphibians. Thus, conservation medicine including therapies targeting the skin will benefit from investigations of amphibian microbial ecology that provide a model for vertebrate host-symbiont interactions on mucosal surfaces. Here, we tested whether the cutaneous microbiota of Panamanian rocket frogs, Colostethus panamansis, was resistant to colonization or altered by treatment. Under semi-natural outdoor mesocosm conditions in Panama, we exposed frogs to one of three treatments including: (1) probiotic - the potentially beneficial bacterium Lysinibacillus fusiformis, (2) transplant – skin washes from the chytridiomycosis-resistant glass frog Espadarana prosoblepon, and (3) control – sterile water. Microbial assemblages were analyzed by a culture-independent T-RFLP analysis. We found that skin microbiota of C. panamansis was resistant to colonization and did not differ among treatments, but shifted through time in the mesocosms. We describe regulation of host AMPs that may function to maintain microbial community stability. Colonization resistance was metabolically costly and microbe-treated frogs lost 7–12% of body mass. The discovery of strong colonization resistance of skin microbiota suggests a well-regulated, rather than dynamic, host-symbiont relationship, and suggests that probiotic therapies aiming to enhance host immunity may require an approach that circumvents host mechanisms maintaining equilibrium in microbial communities.     

Fungal metabolic plasticity and sexual development mediate induced resistance to arthropod fungivory

Prey organisms do not tolerate predator attack passively but react with a multitude of inducible defensive strategies. Although inducible defence strategies are well known in plants attacked by herbivorous insects, induced resistance of fungi against fungivorous animals is largely unknown. Resistance to fungivory is thought to be mediated by chemical properties of fungal tissue, i.e. by production of toxic secondary metabolites. However, whether fungi change their secondary metabolite composition to increase resistance against arthropod fungivory is unknown. We demonstrate that grazing by a soil arthropod, Folsomia candida, on the filamentous fungus Aspergillus nidulans induces a phenotype that repels future fungivores and retards fungivore growth. Arthropod-exposed colonies produced significantly higher amounts of toxic secondary metabolites and invested more in sexual reproduction relative to unchallenged fungi. Compared with vegetative tissue and asexual conidiospores, sexual fruiting bodies turned out to be highly resistant against fungivory in facultative sexual A. nidulans. This indicates that fungivore grazing triggers co-regulated allocation of resources to sexual reproduction and chemical defence in A. nidulans. Plastic investment in facultative sex and chemical defence may have evolved as a fungal strategy to escape from predation.     

Transfer of Alternaria macrospora from Cotton Seed to Seedling: Light and Scanning Electron Microscopy of Colonization

Alternaria macrospora is transferred from an infected seed, through the plant stem to the cotyledon and sporulates on its surface. However, at the beginning of the process, there is no difference between resistant and susceptible plants. In later stages, lower levels of fungal mycelium and sporulation were detected on the seedlings of a resistant cultivar. The fungus grew inside the plant from the underground to the upper parts. The mycelia which originated from surface spores could penetrate, through stomata and result in leaf colonization. A. macrospora sporulated ultimately on plant surfaces whereas the internal leaf tissue was colonized by mycelium only. This study suggests that cotyledon infection is a result of seed infection.     

A multifaceted ecological assessment reveals the invasion of the freshwater red macroalga Montagnia macrospora (Batrachospermales,Rhodophyta) in Taiwan

Invasive freshwater macroalgae are rarely described. Montagnia macrospora is a freshwater red alga introduced from South America to East Asia via the global aquarium trade. The earliest occurrence record of this alga in Taiwan is dated 2005. To determine whether M. macrospora has become invasive in Taiwan and to understand the traits that facilitated its invasion, we took a multifaceted approach that combines examination of ecological background and population genetic analysis. Our island‐wide survey showed that M. macrospora is widespread in the field across Taiwan, where the climate greatly differs from that of South America, and can self‐sustain for nearly a decade. Our population genetic analysis revealed a lack of genetic diversity of M. macrospora in Taiwan, consistent with the hypothesis that the alga expanded through asexual reproduction. Moreover, during our long‐term ecological assessments and field surveys, we observed that M. macrospora is an ecological generalist that can survive in a wide range of temperature, pH, illumination, and nutrient enrichment. Taken together, our data suggest that M. macrospora has successfully invaded the freshwater ecosystems of Taiwan, likely due to its ability to disperse asexually and to grow under broad environmental conditions. We hope that our study brings attention to invasive freshwater algae, which have been overlooked in conservation planning and management.     

Identification and analysis of smORFs in Chlamydomonas reinhardtii

Small open reading frames (smORFs) have been acknowledged as an important partner in organism functions ranging from bacteria to higher eukaryotes. However, there is a lack of investigation of smORFs in green algae, despite their importance in ecology and evolution. We applied bioinformatic analysis, ribosome profiling, and small peptide proteomics to provide a genome-wide and high-confident smORF database in the model green alga Chlamydomonas reinhardtii. The whole genome was screened first to mine potential coding smORFs. Then conservative analysis, ribosome profiling, and proteomics data were processed to identify conserved smORFs and generate translation evidence. The combination of procedures resulted in 2014 smORFs that might exist in the C. reinhardtii genome. The expression of smORFs in Cd treatment suggested that two smORFs might participate in redox reaction, three in inorganic phosphate transport, and one in DNA repair under stress. Our study built a genome-widely database in C. reinhardtii, providing target smORFs for further research.     

Utilizing the green alga Chlamydomonas reinhardtii for microbial electricity generation: a living solar cell

By employing living cells of the green alga Chlamydomonas reinhardtii, we demonstrate the possibility of direct electricity generation from microbial photosynthetic activity. The presented concept is based on an in situ oxidative depletion of hydrogen, photosynthetically produced by C. reinhardtii under sulfur-deprived conditions, by polymer-coated electrocatalytic electrodes.     

Functional Characterization of the Chlamydomonas reinhardtii ERG3 Ortholog,a Gene Involved in the Biosynthesis of Ergosterol

Background

The predominant sterol in the membranes of the alga Chlamydomonas reinhardtii is ergosterol, which is commonly found in the membranes of fungi, but is rarely found in higher plants. Higher plants and fungi synthesize sterols by different pathways, with plants producing cycloartenol as a precursor to end-product sterols, while non-photosynthesizing organisms like yeast and humans produce lanosterol as a precursor. Analysis of the C. reinhardtii genome sequence reveals that this algae is also likely to synthesize sterols using a pathway resembling the higher plant pathway, indicating that its sterols are synthesized somewhat differently than in fungi. The work presented here seeks to establish experimental evidence to support the annotated molecular function of one of the sterol biosynthetic genes in the Chlamydomonas genome.

Methodology/Principal Findings

A gene with homology to the yeast sterol C-5 desaturase, ERG3, is present in the Chlamydomonas genome. To test whether the ERG3 ortholog of C. reinhardtii encodes a sterol C-5 desaturase, Saccharomyces cerevisiae ERG3 knockout strains were created and complemented with a plasmid expressing the Chlamydomonas ERG3. Expression of C. reinhardtii ERG3 cDNA in erg3 null yeast was able to restore ergosterol biosynthesis and reverse phenotypes associated with lack of ERG3 function.

Conclusions/Significance

Complementation of the yeast erg3 null phenotypes strongly suggests that the gene annotated as ERG3 in C. reinhardtii functions as a sterol C-5 desaturase.     

Deodorization of pig slurry and characterization of bacterial diversity using 16S rDNA sequence analysis

Fusarium graminearum is a filamentous fungal plant pathogen that infects major cereal crops. The fungus produces both sexual and asexual spores in order to endure unfavorable environmental conditions and increase their numbers and distribution across plants. In a model filamentous fungus, Aspergillus nidulans, early induction of conidiogenesis is orchestrated by the fluffy genes. The objectives of this study were to characterize fluffy gene homologs involved in conidiogenesis and their mechanism of action in F. graminearum. We characterized five fluffy gene homologs in F. graminearum and found that FlbD is the only conserved regulator for conidiogenesis in A. nidulans and F. graminearum. Deletion of fgflbD prevented hyphal differentiation and the formation of perithecia. Successful interspecies complementation using A. nidulans flbD demonstrated that the molecular mechanisms responsible for FlbD functions are conserved in F. graminearum. Moreover, abaA-wetA pathway is positively regulated by FgFlbD during conidiogenesis in F. graminearum. Deleting fgflbD abolished morphological effects of abaA overexpression, which suggests that additional factors for FgFlbD or an AbaA-independent pathway for conidiogenesis are required for F. graminearum conidiation. Importantly, this study led to the construction of a genetic pathway of F. graminearum conidiogenesis and provides new insights into the genetics of conidiogenesis in fungi.     

种子微生物生态学研究进展

植物种子微生物生态学是研究与种子相联合的微生物的组成﹑功能﹑演替、它们之间关系及其与宿主之间相互关系的科学。种子中蕴含着丰富的微生物资源,它们对种子以及植物的健康具有重要的影响。不同种类植物种子联合的微生物群落由于受到种子本身及外界环境因素的影响而有所差异。论述了种子微生物生态学的概念、主要研究方法、种子微生物生态系统中的微生物种类、相关影响因素,以及种子微生物生态学研究的发展方向。种子微生物生态学的研究对生产实践有重要意义,同时也将丰富种子生物学的内容,对种子科学的发展起到促进作用。     

Regulation of alternative oxidase 1 in Chlamydomonas reinhardtii during sulfur starvation

The mitochondrial respiratory chain in plants, some protists and many fungi consists of the ATP-coupling cyanide-sensitive cytochrome pathway and the cyanide-resistant alternative respiratory pathway. The alternative pathway is mediated by alternative oxidase (AOX). Although AOX has been proposed to play essential roles in nutrient stress tolerance of plants and protists, the effects of sulfur (S) deprivation, on AOX are largely unknown. The unicellular green alga Chlamydomonas reinhardtii reacts to S limitation conditions with the induced expression of many genes. In this work, we demonstrated that exposure of C. reinhardtii to S deprivation results in the up-regulation of AOX1 expression and an increased AOX1 protein. Furthermore, S-deprived C. reinhardtii cells display the enhanced AOX1 capacity. Moreover, nitrate assimilation regulatory protein (NIT2) is involved in the control of the AOX1 gene expression in the absence of S. Together, the results clearly indicate that AOX1 relates to S limitation stress responses and is regulated in a NIT2-dependent manner, probably together with yet-unknown regulatory factor(s).     

Wood decay fungi and their bacterial interaction partners in the built environment – A systematic review on fungal bacteria interactions in dead wood and timber

Microbial biodeterioration of timber and woody material in buildings can cause costly restoration procedures. Here, we focus on Serpula lacrymans (commonly known as dry-rot) the fungus causing the most severe damages to buildings in Europe. Although its morphology, lifestyle, and dispersal have been intensively studied, research on microorganisms sharing the same habitat and interacting with the dry-rot fungus is not as comprehensive. Bacteria have long been known to inhabit dead wood, and several studies have shown their association to fungi. However, their identity, ecology, and putative interactions with co-existing fungi in dead wood remains largely underexplored. The interactions of bacterial and fungi have considerable impact on all partners involved covering the full spectrum between antagonistic and beneficial. Fungi are highly capable of manipulating the microbial community in their surroundings (e.g. via pH manipulation) and bacteria, in turn, can influence fungi by affecting the outcomes of (antagonistic) interactions or preventing fungal feedback inhibition via consumption of breakdown products. Associated bacteria on the other side could play an essential role for the fungus as bacteria can exert significant influence on fungal physiology and behaviour. This minireview summarizes the current knowledge on bacterial-fungal interactions in dead wood with a special focus on dry-rot and proposes possible bacterial-fungal interaction (BFI) mechanisms based on examples from soil or decomposing wood from forests.     

Hyphal morphogenesis in Aspergillus nidulans

The formation of hyphae that grow solely by apical extension is a defining feature of filamentous fungi. Hyphal morphogenesis involves several key steps, including the establishment and maintenance of a stable polarity axis, as well as cell division via the deposition of septa. Several filamentous fungi have been employed in attempts to decipher the mechanisms underlying these steps. Amongst these fungi, Aspergillus nidulans has proven to be a particularly valuable model. The genetic tractability of this fungus coupled with the availability of sophisticated post-genomics resources has enabled the identification and characterization of numerous genes involved in hyphal morphogenesis. Here, we summarize current progress towards understanding the function of these genes and the mechanisms involved in polarized hyphal growth and septation in A. nidulans. We also highlight important areas for future investigation.     

A TRP conductance modulates repolarization after sensory-dependent depolarization in Chlamydomonas reinhardtii

Sensory integration is vital for motile organisms constantly exposed to changing surroundings. Chlamydomonas reinhardtii is a single-celled green alga found swimming in freshwater. In this type of alga, sensory input is first detected by membrane receptors located in the cell body, and then transduced to the beating cilia by membrane depolarization. Many components of the machinery associated with sensory integration in C. reinhardtii, such as chemoreceptors and repolarization-associated channels, are yet uncharacterized. TRP channels are known mediators for cellular sensing in animal cells and it has been suggested that the C. reinhardtii genome encodes for a set of TRP proteins. Here, by combining behavioral studies with electrophysiological experiments conducted on both population and single alga, we test whether TRP channel blockers affect algal swimming behavior. Our results suggest that a TRP conductance is associated to the repolarization that follows a depolarizing receptor potential, highlighting a primitive function of TRP proteins.     

Fungal Parasitism of Heterodera glycines Eggs as Influenced by Egg Age and Pre-colonization of Cysts by Other Fungi

The objective of this study was to determine the effect of egg age and pre-colonization of cysts by a saprophytic or parasitic fungus on parasitism of Heterodera glycines eggs by other parasitic fungi. In agar and in soil tests, fungi generally parasitized more eggs in early developmental stages than eggs containing a juvenile. The effect of pre-colonization of cysts by a fungus on parasitism of eggs by other fungi depended on the fungi involved. In most cases, pre-colonization of cysts by an unidentified, saprophytic fungal isolate (A-1-24) did not affect parasitism of eggs in the cysts subsequently treated with other fungi. However, pre-colonization of cysts by A-1-24 reduced fungal parasitism of eggs in cysts subsequently treated with Cylindrocarpon destructans isolate 3. In agar tests, pre-colonization of cysts by Chaetomium cochliodes, a saprophytic or weakly parasitic fungus, reduced parasitism of eggs in cysts subsequently treated with Verticillium chlamydosporium Florida isolate, Fusarium oxysporum, Fusarium solani, ARF18, and another sterile fungus. However, in soil tests, pre-colonization of cysts by C. cochliodes had no effect on parasitism of eggs by subsequent fungal parasites. In another test, parasitism of eggs by V. chlamydosporium in cysts was not affected by pre-colonizing fungi C. destructans, F. oxysporum, and F. solani but was reduced by Mortierella sp., Pyrenochaeta terrestris, and C. cochliodes. Parasitism of eggs in cysts by ARF18 was reduced by pre-colonizing fungi C. destructans, F. oxysporum, F. solani, P. terrestris, and C. cochliodes but not Mortierella sp.     

Isolation and evaluation of terrestrial fungi with algicidal ability from Zijin Mountain,Nanjing, China

Approximately 60 fungal isolates from Zijin Mountain (Nanjing, China) were screened to determine their algicidal ability. The results show that 8 fungi belonging to Ascomycota and 5 belonging to Basidiomycota have algicidal ability. Of these fungi, Irpex lacteus T2b, Trametes hirsuta T24, Trametes versicolor F21a, and Bjerkandera adusta T1 showed strong algicidal ability. The order of fungal chlorophyll-a removal efficiency was as follows: T. versicolor F21a > I. lacteus T2b > B. adusta T1 > T. hirsuta T24. In particular, T. versicolor F21a completely removed algal cells within 30 h, showing the strongest algicidal ability. The results also show that all 4 fungal species degraded algal cells through direct attack. In addition, most of the tested fungi from the order Polyporales of Basidiomycota exhibited strong algicidal activity, suggesting that most fungi that belong to this order have algicidal ability. The findings of this work could direct the search for terrestrial fungi for bloom control.