Studies on the body wall ultrastructure of Hirschmanniella oryzae and H. spinicaudata (Nematoda : Pratylenchidae)

L'ultrastructure de la cuticule et de la musculature somatique chez #Hirschmanniella oryzae et #H. spinicaudata est décrite. La cuticule est constituée de trois zones : une zone corticale avec deux couches (une couche trilamellaire externe et une couche interne d'aspect granuleux), une zone médiane formée d'une couche vacuolaire et une zone basale représentée par une couche striée. Sous les champs latéraux, la structure de la zone corticale demeure inchangée ; par contre, la couche vacuolaire est remplacée par quatre couches (deux couches vacuolaires séparées par deux autres d'aspect granuleux) ; la couche basale striée s'interrompt sous les incisures externes du champ latéral ; elle est remplacée par deux couches épaisses d'aspect fibreux. L'observation des champs musculaires montre que les "Thorneian cells" de Sher (1968) correspondent à une hypertrophie de la partie sarcoplasmique des cellules musculaires, chargées d'importantes réserves de glycogène. Ces observations sur l'accumulation inhabituelle de glycogène sont discutées. (Résumé d'auteur

Description of Aphasmatylenchus liberiensis n. sp., and observations on the other species of the genus Aphasmatylenchus Sher, 1965 (Nematoda : Hoplolaimidae)

La population d'#Aphasmatylenchus précédemment identifiée comme #A. nigeriensis par Vovlas et al. (1991) est considérée comme une nouvelle espèce, décrite et illustrée ici comme #A. liberiensis n. sp. ; ses principaux caractères distinctifs sont le premier anneau céphalique non divisé, l'absence de spermatozoïdes dans le tractus génital de la femelle et l'absence de mâles. Des observations en microscopie électronique à balayage et optique ont été conduites sur des populations ouest-africaines d'#Aphasmatylenchus ; la morphologie externe de la capsule céphalique est schématisée pour toutes les espèces du genre. La variabilité des structures externes est très faible, à l'exception de la configuration du premier anneau céphalique. Des fasciculi ont été observés pour la première fois chez #A. nigeriensis provenant du Sud-Ouest de la Côte d'Ivoire, tandis que des appendices filiformes ont été détectés sur la marge de la lèvre cloacale antérieure chez #A. straturatus et #A. variabilis, appendices précédemment identifiés dans le genre #Radopholus ; la présence de nerfs dans ces structures ne peut pas être confirmée au microscopie électronique à balayage. (Résumé d'auteur

Defining trait-based microbial strategies with consequences for soil carbon cycling under climate change

We acknowledge funding from the US DOE Genomic Science Program, BER, Office of Science project DE-SC0016410. We thank Bin Wang for discussion and inputs on trait-based modelling.Peer reviewedPublisher PD

Cellulolytic potential under environmental changes in microbial communities from grassland litter

In many ecosystems, global changes are likely to profoundly affect microorganisms. In Southern California, changes in precipitation and nitrogen deposition may influence the composition and functional potential of microbial communities and their resulting ability to degrade plant material. To test whether such environmental changes impact the distribution of functional groups involved in leaf litter degradation, we determined how the genomic diversity of microbial communities in a semi-arid grassland ecosystem changed under reduced precipitation or increased N deposition. We monitored communities seasonally over a period of 2 years to place environmental change responses into the context of natural variation. Fungal and bacterial communities displayed strong seasonal patterns, Fungi being mostly detected during the dry season whereas Bacteria were common during wet periods. Most putative cellulose degraders were associated with 33 bacterial genera and predicted to constitute 18% of the microbial community. Precipitation reduction reduced bacterial abundance and cellulolytic potential whereas nitrogen addition did not affect the cellulolytic potential of the microbial community. Finally, we detected a strong correlation between the frequencies of genera of putative cellulose degraders and cellulase genes. Thus, microbial taxonomic composition was predictive of cellulolytic potential. This work provides a framework for how environmental changes affect microorganisms responsible for plant litter deconstruction

Microzooplankton regulation of surface ocean POC:PON ratios

The elemental composition of particulate organic matter in the surface ocean significantly affects the efficiency of the ocean's store of carbon. Though the elemental composition of primary producers is an important factor, recent observations from the western North Atlantic Ocean revealed that carbon-to-nitrogen ratios (C:N) of phytoplankton were significantly higher than the relatively homeostatic ratio of the total particulate pool (particulate organic carbon:particulate organic nitrogen; POC:PON). Here we use an idealized ecosystem model to show how interactions between primary and secondary producers maintain the mean composition of surface particulates and the difference between primary producers and bulk material. Idealized physiological models of phytoplankton and microzooplankton, constrained by laboratory data, reveal contrasting autotrophic and heterotrophic responses to nitrogen limitation: under nitrogen limitation, phytoplankton accumulate carbon in carbohydrates and lipids while microzooplankton deplete internal C reserves to fuel respiration. Global ecosystem simulations yield hypothetical global distributions of phytoplankton and microzooplankton C:N ratio predicting elevated phytoplankton C:N ratios in the high-light, low-nutrient regions of the ocean despite a lower, homeostatic POC:PON ratio due to respiration of excess carbon in systems subject to top-down control. The model qualitatively captures and provides a simple interpretation for, a global compilation of surface ocean POC:PON data

Taxonomic studies on the genus Aorolaimus Sher, 1963 (Nemata : Hoplolaimidae) : 1. Bibliographic analysis and tentative key to species

L'analyse bibliographique des descriptions d'espèces ou de populations dans le genre #Aorolaimus permet d'évaluer la variabilité intraspécifique des 39 caractères utilisés pour les diagnoses spécifiques ou les relations entre taxons dans ce genre. Trois caractères (aréolations au niveau de la phasmide dans les champs latéraux, position de la phasmide antérieure, existence de mâles) sont bien définis et présentent une variabilité intraspécifique faible et intragénérique suffisante pour proposer six groupes d'espèces à l'intérieur desquels les autres caractères morpho-biométriques ne permettent pas une séparation claire de toutes les espèces. Plusieurs espèces du genre #Aorolaimus apparaissent donc douteuses et leur réexamen de microscopie optique est nécessaire. #Peltamigratus regularis Siddiqi, 1985 est transféré au genre #Aorolaimus comme #Aorolaimus regularis (Siddiqi, 1985) n. comb. #A. brevicaudatus, A. conicori et #A. triticeus sont considérés comme synonymes mineurs de #A. longistylus et #A. thornei comme synonyme mineur de #A. pachyurus. (Résumé d'auteur

Differential Response of Bacterial Microdiversity to Simulated Global Change

ACKNOWLEDGMENTS UC Irvine and the LRGCE are located on the ancestral homelands of the Indigenous Kizh and Acjachemen nations. We thank Alejandra Rodriguez Verdugo, Katrine Whiteson, Kendra Walters, Cynthia Rodriguez, Kristin Barbour, Alberto Barron Sandoval, Joanna Wang, Joia Kai Capocchi, Pauline Uyen Phuong Nguyen, Khanh Thuy Huynh, and Clara Barnosky for their input on analyses and previous drafts and for laboratory help. This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research grants DE-SC0016410 and DE-SC0020382.Peer reviewedPublisher PD

Combination of MALDI-TOf mass spectrometry and machine learning for rapid antimicrobial resistance screening: the CASE of Campylobacter spp

While MALDI-TOF mass spectrometry (MS) is widely considered as the reference method for the rapid and inexpensive identification of microorganisms in routine laboratories, less attention has been addressed to its ability for detection of antimicrobial resistance (AMR). Recently, some studies assessed its potential application together with machine learning for the detection of AMR in clinical pathogens. The scope of this study was to investigate MALDI-TOF MS protein mass spectra combined with a prediction approach as an AMR screening tool for relevant foodborne pathogens, such as Campylobacter coli and Campylobacter jejuni. A One-Health panel of 224 C. jejuni and 116 C. coli strains was phenotypically tested for seven antimicrobial resistances, i.e., ciprofloxacin, erythromycin, tetracycline, gentamycin, kanamycin, streptomycin, and ampicillin, independently, and were submitted, after an on- and off-plate protein extraction, to MALDI Biotyper analysis, which yielded one average spectra per isolate and type of extraction. Overall, high performance was observed for classifiers detecting susceptible as well as ciprofloxacin- and tetracycline-resistant isolates. A maximum sensitivity and a precision of 92.3 and 81.2%, respectively, were reached. No significant prediction performance differences were observed between on- and off-plate types of protein extractions. Finally, three putative AMR biomarkers for fluoroquinolones, tetracyclines, and aminoglycosides were identified during the current study. Combination of MALDI-TOF MS and machine learning could be an efficient and inexpensive tool to swiftly screen certain AMR in foodborne pathogens, which may enable a rapid initiation of a precise, targeted antibiotic treatment