BACKGROUND: The backbone of the eukaryotic tree of life contains taxa only found in molecular surveys, of which we still have a limited understanding. Such is the case of Picozoa, an enigmatic lineage of heterotrophic picoeukaryotes within the supergroup Archaeplastida, which has emerged as a significant component of marine microbial planktonic communities. To enhance our understanding of the diversity, distribution, and ecology of Picozoa, we conduct a comprehensive assessment at different levels, from assemblages to taxa, employing phylogenetic analysis, species distribution modeling, and ecological niche characterization.
RESULTS: Picozoa was among the ten most abundant eukaryotic groups, found almost exclusively in marine environments. The phylum was represented by 179 Picozoa\'s OTU (pOTUs) placed in five phylogenetic clades. Picozoa community structure had a clear latitudinal pattern, with polar assemblages tending to cluster separately from non-polar ones. Based on the abundance and occupancy pattern, the pOTUs were classified into four categories: Low-abundant, Widespread, Polar, and Non-polar. We calculated the ecological niche of each of these categories. Notably, pOTUs sharing similar ecological niches were not closely related species, indicating a phylogenetic overdispersion in Picozoa communities. This could be attributed to competitive exclusion and the strong influence of the seasonal amplitude of variations in environmental factors, such as temperature, shaping physiological and ecological traits.
CONCLUSIONS: Overall, this work advances our understanding of uncharted protists\' evolutionary dynamics and ecological strategies. Our results highlight the importance of understanding the species-level ecology of marine heteroflagellates like Picozoa. The observed phylogenetic overdispersion challenges the concept of phylogenetic niche conservatism in protist communities, suggesting that closely related species do not necessarily share similar ecological niches. Video Abstract.

Bartonella is a bacterial genus that comprises arthropod-borne microorganisms. Several Bartonella isolates have been detected from bats worldwide, which are thought to be undescribed species. We aimed to test the presence of Bartonella spp. among bats from Colombia, and evaluate the genetic diversity of bat-associated Bartonella spp. through phylogenetic analyses. A total of 108 bat blood samples were collected from three bat species (Carollia perspicillata, Mormoops megalophylla, and Natalus tumidirostris) that inhabit the Macaregua cave. The Bartonella ssrA gene was targeted through real-time and end-point PCR; additionally, the gltA and rpoB genes were detected by end-point PCR. All obtained amplicons were purified and bidirectionally sequenced for phylogenetic analysis using a concatenated supermatrix and a supertree approaches. A detection frequency of 49.1 % (53/108) for Bartonella spp. was evidenced among bat blood samples, of which 59.1 % (26/44), 54.3 % (19/35) and 27.6 % (8/29) were identified in Carollia perspicillata, Natalus tumidirostris and Mormoops megalophylla respectively. A total of 35 ssrA, 5 gltA and 4 rpoB good-quality sequences were obtained which were used for phylogenetic analysis. All obtained bat sequences clustered together with sequences obtained from Neotropical bat species into two bat-restricted clades namely clade A and clade N. We detected the presence of Bartonella spp. that clustered within two different bat-associated Bartonella clades, giving the first data of the genetic diversity of these bacteria among bats from Colombia.

Metabarcoding analysis has been demonstrated to be an effective technology for monitoring diversity and dynamics of phytoplankton including Skeletonema species. Although molecular diversity uncovered in metabarcoding projects has generally been interpreted as sum of interspecies diversity and intraspecies diversity, accumulating evidence suggests that it also harbors unprecedentedly high levels of intra-genomic variations (IGVs). As up to thousands of amplicon sequence variants (ASVs) identified in a typical metabarcoding project can be annotated to be Skeletonema species, we hypothesize that substantial portions of these ASVs are contributed by IGVs. Here, the nature of IGVs in Skeletonema species was quantitatively analyzed by carrying out single-strain metabarcoding analysis of 18S rDNA V4 in 49 strains belonging to seven Skeletonema species. Results showed that each Skeletonema strain harbored a high level of IGVs as expected. While many Skeletonema strains each contained one dominant ASV and a substantial number of ASVs displaying much lower relative abundance, other Skeletonema strains each contained multiple ASVs with comparable or nearly equally abundances. Thus the co-existence of multiple dominant ASVs in a single cell indicated a tug-of-war of these variants in evolution, which may eventually result in harmonized coexistence of multiple dominant ASVs. A total of nine dominant ASVs and 652 non-dominant ASVs were found in 49 strains of seven Skeletonema species, indicating rich interspecies and intraspecies variations, and complex evolution of IGVs in genus of Skeletonema. The results confirmed that the extensive degree of IGVs was the main contributor to the high molecular diversity revealed by metabarcoding analysis. This study highlights the importance of quantitative characterization of IGVs in Skeletonema species for accurate interpretation of species diversity in metabarcoding analysis.

In recent years, significant advancements have been made in molecular generation algorithms aimed at facilitating drug development, and molecular diversity holds paramount importance within the realm of molecular generation. Nonetheless, the effective quantification of molecular diversity remains an elusive challenge, as extant metrics exemplified by Richness and Internal Diversity fall short in concurrently encapsulating the two main aspects of such diversity: quantity and dissimilarity. To address this quandary, we propose Hamiltonian diversity, a novel molecular diversity metric predicated upon the shortest Hamiltonian circuit. This metric embodies both aspects of molecular diversity in principle, and we implement its calculation with high efficiency and accuracy. Furthermore, through empirical experiments we demonstrate the high consistency of Hamiltonian diversity with real-world chemical diversity, and substantiate its effects in promoting diversity of molecular generation algorithms. Our implementation of Hamiltonian diversity in Python is available at: https://github.com/HXYfighter/HamDiv .Scientific contributionWe propose a more rational molecular diversity metric for the community of cheminformatics and drug development. This metric can be applied to evaluation of existing molecular generation methods and enhancing drug design algorithms.

The cultivation of pineapple (Ananas comosus) is threatened worldwide by mealybug wilt disease of pineapple (MWP), whose etiology is not yet fully elucidated. In this study, we characterized pineapple mealybug wilt-associated ampeloviruses (PMWaVs, family Closteroviridae) from a diseased pineapple plant collected from Reunion Island, using a high-throughput sequencing approach combining Illumina short reads and Nanopore long reads. Reads co-assembly resulted in complete or near-complete genomes for six distinct ampeloviruses, including the first complete genome of pineapple mealybug wilt-associated virus 5 (PMWaV5) and that of a new species tentatively named pineapple mealybug wilt-associated virus 7 (PMWaV7). Short reads data provided high genome coverage and sequencing depths for all six viral genomes, contrary to long reads data. The 5\' and 3\' ends of the genome for most of the six ampeloviruses could be recovered from long reads, providing an alternative to RACE-PCRs. Phylogenetic analyses did not unveil any geographic structuring of the diversity of PMWaV1, PMWaV2 and PMWaV3 isolates, supporting the current hypothesis that PMWaVs were mainly spread by human activity and vegetative propagation.

Tripos is a large dinoflagellate genus widely distributed in the world\'s oceans. Morphology-based species identification is inconclusive due to high morphological intraspecific variability. Metabarcoding analysis has been demonstrated to be effective for species identification and tracking their spatiotemporal dynamics. However, accumulating evidence suggests high levels of intragenomic variations (IGVs) are common in many algae, leading to concerns about overinterpretation of molecular diversity in metabarcoding studies. In this project, we evaluated and compared IGVs in Tripos species by conducting the first high-throughput sequencing (HTS) of 18S rDNA V4 of Tripos single cells. High numbers of haplotypes (19-172) were identified in each of the 30 Tripos cells. Each cell contained one dominant haplotype with high relative abundance and many haplotypes with lower abundances. Thus, the presence of multiple minor haplotypes substantially overestimate the molecular diversity identified in metabarcoding analysis, which encompass not only interspecific and intraspecific diversities, but high levels of IGVs.

Based on the nucleotide sequences of the mitochondrial genome (mitogenome) of specimens taken from two mussel species (Arcuatula senhousia and Mytilus coruscus), an investigation was performed by means of the complex approaches of the genomics, molecular phylogenetics, and evolutionary genetics. The mitogenome structure of studied mussels, like in many other invertebrates, appears to be much more variable than in vertebrates and includes changing gene order, duplications, and deletions, which were most frequent for tRNA genes; the mussel species\' mitogenomes also have variable sizes. The results demonstrate some of the very important properties of protein polypeptides, such as hydrophobicity and its determination by the purine and pyrimidine nucleotide ratio. This fact might indirectly indicate the necessity of purifying natural selection for the support of polypeptide functionality. However, in accordance with the widely accepted and logical concept of natural cutoff selection for organisms living in nature, which explains its action against deleterious nucleotide substitutions in the nonsynonymous codons (mutations) and its holding of the active (effective) macromolecules of the polypeptides in a population, we were unable to get unambiguous evidence in favor of this concept in the current paper. Here, the phylogeny and systematics of mussel species from one of the largest taxons of bivalve mollusks are studied, the family known as Mytilidae. The phylogeny for Mytilidae (order Mytilida), which currently has no consensus in terms of systematics, is reconstructed using a data matrix of 26-27 mitogenomes. Initially, a set of 100 sequences from GenBank were downloaded and checked for their gender: whether they were female (F) or male (M) in origin. Our analysis of the new data confirms the known drastic differences between the F/M mitogenome lines in mussels. Phylogenetic reconstructions of the F-lines were performed using the combined set of genetic markers, reconstructing only protein-coding genes (PCGs), only rRNA + tRNA genes, and all genes. Additionally, the analysis includes the usage of nucleotide sequences composed of other data matrices, such as 20-68 mitogenome sequences. The time of divergence from MRCA, estimated via BEAST2, for Mytilidae is close to 293 Mya, suggesting that they originate in the Silurian Period. From all these data, a consensus for the phylogeny of the subfamily of Mytilinae and its systematics is suggested. In particular, the long-debated argument on mussel systematics was resolved as to whether Mytilidae, and the subfamily of Mytilinae, are monophyletic. The topology signal, which was strongly resolved in this paper and in the literature, has refuted the theory regarding the monophyly of Mytilinae.

Noroviruses constitute a significant aetiology of sporadic and epidemic gastroenteritis in human hosts worldwide, especially among young children, the elderly, and immunocompromised patients. The low infectious dose of the virus, protracted shedding in faeces, and the ability to persist in the environment promote viral transmission in different socioeconomic settings. Considering the substantial disease burden across healthcare and community settings and the difficulty in controlling the disease, we review aspects related to current knowledge about norovirus biology, mechanisms driving the evolutionary trends, epidemiology and molecular diversity, pathogenic mechanism, and immunity to viral infection. Additionally, we discuss the reservoir hosts, intra-inter host dynamics, and potential eco-evolutionary significance. Finally, we review norovirus vaccines in the development pipeline and further discuss the various host and pathogen factors that may complicate vaccine development.

Globally, rotavirus continues to be the leading etiology of severe pediatric gastroenteritis, and transmission of the disease via environmental reservoirs has become an emerging concern in developing countries. From August to October 2021, a total of 69 samples comprising 48 of raw and treated sewage, and 21 surface waters, were collected from four Durban wastewater treatment plants (DWWTP), and effluent receiving rivers, respectively. Rotaviruses recovered and identified from the samples were subjected to sequencing, genotyping, and phylogenetic analysis. Of the 65 (94.2%) rotavirus-positive samples, 33.3% were from raw sewage, 16% from activated sludge, 15.9% from final effluents, and 29.0% were from the receiving river samples. A total of 49 G and 41 P genotypes were detected in sewage while 15 G and 22 P genotypes were detected in river samples. G1 genotype predominated in sewage (24.5%) followed by G3 (22.4%), G2 (14.3%), G4 (12.2%), G12 (10.2%), G9 (8.2%), and G8 (6.1%). Similarly, G1 predominated in river water samples (33.3%) and was followed by G2, G4 (20.0% each), G3, and G12 (13.3% each). Rotavirus VP4 genotypes P[4], P[6], and P[8] accounted for 36.6%, 29.3%, and 9.8%, respectively, in sewage. Correspondingly, 45.5%, 31.8%, and 13.6% were detected in river samples. The G and P genotypes not identified by the methods used were 2.1% versus 24.3% and 0.1% versus 9.1% for sewage and river water samples, respectively. Sequence comparison studies indicated a high level of nucleotide identity in the G1, G2, G3, G4, G8 VP7, and P[4], P[6], and P[8] VP4 gene sequences between strains from the environment and those from patients in the region. This is the first environmental-based study on the G and P genotypes diversity of rotavirus in municipal wastewater and their receiving rivers in this geographical region. The high similarity between environmental and clinical rotavirus strains suggests both local circulation of the virus and potential exposure risks. In addition, it highlights the usefulness of sewage surveillance as an additional tool for an epidemiological investigation, especially in populations that include individuals with subclinical or asymptomatic infections that are precluded in case-based studies.

This study introduces a novel organosilicon-modified polysaccharide (Si-AP) synthesized via grafting and comprehensively evaluates its performance in water-based drilling fluids (WBDFs). The molecular structure of Si-AP was characterized using Fourier-transform infrared spectroscopy (FTIR) and 1H-NMR experiments. Thermalgravimetric analysis (TGA) confirmed the good thermal stability of Si-AP up to 235 °C. Si-AP significantly improves the rheological properties and fluid loss performance of WBDFs. With increasing Si-AP concentration, system viscosity increases, API filtration rate decreases, clay expansion is inhibited, and drilling cuttings hydration dispersion is suppressed, especially under high-temperature conditions. Additionally, mechanistic analysis indicates that the introduction of siloxane groups can effectively inhibit the thermal degradation of AP chains and enhance their high-temperature resistance. Si-AP can form a lubricating film by adsorbing on the surface of clay particles, improving mud cake quality, reducing the friction coefficient, and significantly enhancing the lubricating performance of WBDFs. Overall, Si-AP exhibits a higher temperature-resistance limit compared to AP and more effectively optimizes the lubrication, inhibition, and control of the filtration rate of WBDFs under high-temperature conditions. While meeting the requirements of drilling fluid systems under high temperatures, Si-AP also addresses environmental concerns and holds promise as an efficient solution for the exploitation of deep-seated oil and gas resources.