Agricultural and Biological Sciences (miscellaneous)

AbstractThe unicellular cyanobacterium Candidatus Atelocyanobacterium thalassa (UCYN‐A) is a key diazotroph in the global ocean owing to its high N2 fixation rates and wide distribution in marine environments. Nevertheless, little is known about UCYN‐A in oxygen‐deficient zones (ODZs), which may be optimal environments for marine diazotrophy. Therefore, the distribution and diversity of UCYN‐A were studied in two consecutive years under contrasting phases (La Niña vs. El Niño) of El Niño Southern Oscillation (ENSO) along a transect in the ODZ of the Mexican Pacific upwelling system. Of the three UCYN‐A sublineages found, UCYN‐A1 and UCYN‐A3 were barely detected, whereas UCYN‐A2 was dominant in all the stations and showed a wide distribution in both ENSO phases. The presence of UCYN‐A was associated with well‐oxygenated waters, but it was also found for the first time under suboxic conditions (<20 μM) at the bottom of a shallow coastal station, within the oxygen‐poor and nutrient‐rich Subsurface Subtropical water mass. This study contributes to the understanding of UCYN‐A distribution under different oceanographic conditions associated with ENSO phases in upwelling systems, especially because of the current climate change and increasing deoxygenation in many areas of the world's oceans.

<p><strong>Background.</strong> Climate change models have projected an increase in the distribution of certain crop pests of economic importance by forecasting more favorable future conditions for these organisms. In citrus farming, Huanglongbing is one of the most devastating diseases worldwide, since it has caused the death of millions of trees. <strong>Objetive.</strong> The objective of this study was to estimate the current and future distribution of <em>Candidatus </em>Liberibacter asiaticus in Mexico, under the climate change scenarios SSP2 4.5 and SSP5 8.5, for the years 2050 and 2070. <strong>Methodology.</strong> Distribution models were generated with MaxEnt and R, using uncorrelated bioclimatic variables from eight General Circulation Models (GCM) derived from CMIP6 and disease presence data. <strong>Results.</strong> The results indicate that the current suitability is 44.6 %. The future distribution depended on how model predictions were pooled. An optimistic approach that considered the intersection of all models showed a small reduction of 4.1% while, considering the union of all the GCM models, the increase will vary from 12.3 to 20.1 % of the Mexican territory depending on the particular scenario and time projection. <strong>Implications.</strong> The zones of potential occurrence of <em>Candidatus </em>Liberibacter asiaticus include most of the citrus-growing areas in Mexico. <strong>Conclusion. </strong>In some regions, future scenarios show a reduction in the potential occurrence of the species in citrus plantations. However, the risk remains because its surroundings include suitable areas that can be sources of dissemination of the disease. </p>

Huanglongbing (HLB) is a devastating citrus disease caused by Candidatus Liberibacter asiaticus (CLas). Since its initial outbreak in Guangdong Province, China, it has spread to 10 provinces and caused significant economic losses. Hence, assessing CLas genetic diversity and demographic history is crucial for HLB epidemic prevention and control. In this study, we collected 500 leaf samples of CLas-infected plants from 10 provinces. We performed multi-loci sequence analysis on four gene fragments (omp, DnaA, GroEL, and SDE1) to explore the genetic differentiation and diversity of CLas in China. Our results indicated low nucleotide diversity (0.00005 ± 0.00001) in CLas, with the absence of significant systematic geographic structure in its distribution. Molecular variance analysis revealed predominant (81.7%) genetic variations within the population, with a minor variation (18.3%) occurring between populations as well as Yunnan provinces. In the Fujian population, significant gene exchange occurred with the other nine populations. Significant negative values in Tajima’s D and Fu’s FS neutrality tests indicated historical population expansions. The nucleotide mismatch distribution curve exhibits a single peak pattern, further supporting the expansion events. Our findings hold potential for advancing epidemiological research and providing suggestions for effective strategies to mitigate the spread of CLas and control HLB.

Symbiotic associations between bacteria and ciliate protists are rather common. In particular, several cases were reported involving bacteria of the alphaproteobacterial lineage Rickettsiales, but the diversity, features, and interactions in these associations are still poorly understood. In this work, we characterized a novel ciliate protist strain originating from Brazil and its associated Rickettsiales endosymbiont by means of live and ultrastructural observations, as well as molecular phylogeny. Though with few morphological peculiarities, the ciliate was found to be phylogenetically affiliated with Pseudokeronopsis erythrina, a euryhaline species, which is consistent with its origin from a lagoon with significant spatial and seasonal salinity variations. The bacterial symbiont was assigned to “Candidatus Trichorickettsia mobilis subsp. hyperinfectiva”, being the first documented case of a Rickettsiales associated with urostylid ciliates. It resided in the host cytoplasm and bore flagella, similarly to many, but not all, conspecifics in other host species. These findings highlight the ability of “Candidatus Trichorickettsia” to infect multiple distinct host species and underline the importance of further studies on this system, in particular on flagella and their regulation, from a functional and also an evolutionary perspective, considering the phylogenetic proximity with the well-studied and non-flagellated Rickettsia.