Publications

4381

Bactericera cockerelli es una plaga de importancia económica en solanáceas en México, por los amarillamientos que causa en los cultivos, así como por la transmisión de Candidatus Liberibacter solanacearum. Se describen variantes genéticas de este insecto, las cuales se relacionan con su capacidad para fungir como vector. En México, la distribución de B. cockerelli es muy amplia y se carece de información acerca de sus características morfológicas y genéticas. El objetivo de esta investigación fue caracterizar morfológica y genéticamente a B. cockerelli y detectar la presencia de Ca. L. solanacearum en poblaciones de B. cockerelli de las zonas productoras de solanáceas en México. Para lo cual se muestrearon 35 localidades de 13 estados, sobre cultivos de chile, tomate, berenjena y papa, bajo diferentes sistemas de producción. Se midieron las variables largas de cuerpo (LC), largas de abdomen (LAB) y ancho de abdomen (AAB) en insectos de cada población, se detectó la presencia de Ca. L. solanacearum en los 13 estados muestreados, donde los machos presentaron el mayor porcentaje de insectos positivos. La presencia de Ca. L. solanacearum no se vio influenciada por el hospedero o el sistema de producción, sino por la presencia de B. cockerelli.

Citrus Huanglongbing (HLB; yellow shoot disease) is associated with an unculturable α-proteobacterium “Candidatus Liberibacter asiaticus” (CLas). HLB was found in southern California in 2012, and the current management strategy is based on suppression of the Asian citrus psyllid (Diaphorina citri) that transmits CLas and removal of confirmed CLas-positive trees. Little is known about Asian citrus psyllid-associated bacteria and citrus-associated bacteria in the HLB system. Such information is important in HLB management, particularly for accurate detection of CLas. Recent advancements in next-generation sequencing technology provide new opportunities to study HLB through genomic DNA sequence analyses (metagenomics). In this study, HLB-related bacteria in Asian citrus psyllid and citrus (represented by leaf midrib tissues) samples from southern California were analyzed. A metagenomic pipeline was developed to serve as a prototype for future bacteriomic research. This pipeline included steps of next-generation sequencing in Illumina platform, de novo assembly of Illumina reads, sequence classification using the Kaiju tool, acquisition of bacterial draft genome sequences, and taxonomic validation and diversity evaluation using average nucleotide identity. The identified bacteria in Asian citrus psyllids and citrus together included Bradyrhizobium, Buchnera, Burkholderia, “Candidatus Profftella armature,” “Candidatus Carsonella ruddii,” CLas, Mesorhizobium, Paraburkholderia, Pseudomonas, and Wolbachia. The whole genome of a CLas strain recently found in San Bernardino County was sequenced and classified into prophage typing group 1 (PTG-1), one of the five known CLas groups in California. Based on sequence similarity, Bradyrhizobium and Mesorhizobium were identified as possible source that could interfere with CLas detection using the 16S rRNA gene-based PCR commonly used for HLB diagnosis, particularly at low or zero CLas titer situation.

Streptomycin (STR) has been used to control citrus huanglongbing (HLB) caused by ‘Candidatus Liberibacter asiaticus’ (CLas) via foliar spray. Here, we studied the residue dynamics of STR and its effect on CLas titers in planta applied by foliar spray and trunk injection of 3-year-old citrus trees that were naturally infected by CLas in the field. After foliar spray, STR levels in leaves peaked at 2 to 7 days postapplication (dpa) and gradually declined thereafter. The STR spray did not significantly affect CLas titers in leaves of treated plants as determined by quantitative PCR. After trunk injection, peak levels of STR were observed 7 to 14 dpa in the leaf and root tissues, and near-peak levels were sustained for another 14 days before significantly declining. At 12 months after injection, moderate to low or undetectable levels of STR were observed in the leaf, root, and fruit, depending on the doses of STR injected, with a residue level of 0.28 µg/g in harvested fruit at the highest injection concentration of 2.0 µg/tree. CLas titers in leaves were significantly reduced by trunk injection of STR at 1.0 or 2.0 g/tree, starting from 7 dpa and throughout the experimental period. The reduction of CLas titers was positively correlated with STR residue levels in leaves. The in planta minimum effective concentration of STR needed to suppress the CLas titer to an undetectable level (cycle threshold ≥36.0) was 1.92 µg/g fresh weight. Determination of the in planta minimum effective concentration of STR against CLas and its spatiotemporal residue levels in planta provides the guidance to use STR for HLB management.

Summary Thermoplasmata is a widely distributed and ecologically important archaeal class in the phylum Euryarchaeota. Because few cultures and genomes are available, uncharacterized Thermoplasmata metabolisms remain unexplored. In this study, we obtained four medium‐ to high‐quality archaeal metagenome‐assembled genomes (MAGs) from the filamentous fragments of black‐odorous aquatic sediments (Foshan, Guangdong, China). Based on their 16S rRNA gene and ribosomal protein phylogenies, the four MAGs belong to the previously unnamed Thermoplasmata UBA10834 clade. We propose that this clade (five reference genomes from the Genome Taxonomy Database (GTDB) and four MAGs from this study) be considered a new order, Candidatus Gimiplasmatales. Metabolic pathway reconstructions indicated that the Ca . Gimiplasmatales MAGs can biosynthesize isoprenoids and nucleotides de novo . Additionally, some taxa have genes for formaldehyde and acetate assimilation, and the Wood–Ljungdahl CO 2 ‐fixation pathway, indicating a mixotrophic lifestyle. Sulfur reduction, hydrogen metabolism, and arsenic detoxification pathways were predicted, indicating sulfur‐, hydrogen‐, and arsenic‐transformation potentials. Comparative genomics indicated that the H 4 F Wood–Ljungdahl pathway of both Ca . Gimiplasmatales and Methanomassiliicoccales was likely obtained by the interdomain lateral gene transfer from the Firmicutes. Collectively, this study elucidates the taxonomic and potential metabolic diversity of the new order Ca . Gimiplasmatales and the evolution of this subgroup and its sister lineage Methanomassiliicoccales.