Ontogenetic Change in the Venom of Mexican Black-Tailed Rattlesnakes (Crotalus molossus nigrescens)

Ontogenetic changes in venom composition have important ecological implications due the relevance of venom in prey acquisition and defense. Additionally, intraspecific venom variation has direct medical consequences for the treatment of snakebite. However, ontogenetic changes are not well documented in most species. The Mexican Black-tailed Rattlesnake (Crotalus molossus nigrescens) is large-bodied and broadly distributed in Mexico. To document venom variation and test for ontogenetic changes in venom composition, we obtained venom samples from twenty-seven C. m. nigrescens with different total body lengths (TBL) from eight states in Mexico. The primary components in the venom were detected by reverse-phase HPLC, western blot, and mass spectrometry. In addition, we evaluated the biochemical (proteolytic, coagulant and fibrinogenolytic activities) and biological (LD₅₀ and hemorrhagic activity) activities of the venoms. Finally, we tested for recognition and neutralization of Mexican antivenoms against venoms of juvenile and adult snakes. We detected clear ontogenetic venom variation in C. m. nigrescens. Venoms from younger snakes contained more crotamine-like myotoxins and snake venom serine proteinases than venoms from older snakes; however, an increase of snake venom metalloproteinases was detected in venoms of larger snakes. Venoms from juvenile snakes were, in general, more toxic and procoagulant than venoms from adults; however, adult venoms were more proteolytic. Most of the venoms analyzed were hemorrhagic. Importantly, Mexican antivenoms had difficulties recognizing low molecular mass proteins (<12 kDa) of venoms from both juvenile and adult snakes. The antivenoms did not neutralize the crotamine effect caused by the venom of juveniles. Thus, we suggest that Mexican antivenoms would have difficulty neutralizing some human envenomations and, therefore, it may be necessary improve the immunization mixture in Mexican antivenoms to account for low molecular mass proteins, like myotoxins.

The plant beneficial rhizobacterium Achromobacter sp. 5B1 influences root development through auxin signaling and redistribution

Roots provide physical and nutritional support to plant organs that are above ground and play critical roles for adaptation via intricate movements and growth patterns. Through screening the effects of bacterial isolates from roots of halophyte Mesquite (Prosopis sp.) on Arabidopsis thaliana, we identified Achromobacter sp. 5B1 as a probiotic bacterium that influences plant functional traits. Detailed genetic and architectural analyses in Arabidopsis grown in vitro and in soil, cell division measurements, auxin transport and response gene expression and brefeldin A treatments demonstrated that root colonization with Achromobacter sp. 5B1 changes the growth and branching patterns of roots, which were related to auxin perception and redistribution. Expression analysis of auxin transport and signaling revealed a redistribution of auxin within the primary root tip of wild-type seedlings by Achromobacter sp. 5B1 that is disrupted by brefeldin A and correlates with repression of auxin transporters PIN1 and PIN7 in root provasculature, and PIN2 in the epidermis and cortex of the root tip, whereas expression of PIN3 was enhanced in the columella. In seedlings harboring AUX1, EIR1, AXR1, ARF7ARF19, TIR1AFB2AFB3 single, double or triple loss-of-function mutations, or in a dominant (gain-of-function) mutant of SLR1, the bacterium caused primary roots to form supercoils that are devoid of lateral roots. The changes in growth and root architecture elicited by the bacterium helped Arabidopsis seedlings to resist salt stress better. Thus, Achromobacter sp. 5B1 fine tunes both root movements and the auxin response, which may be important for plant growth and environmental adaptation.

HR4 gene is induced in the Arabidopsis-Trichoderma atroviride beneficial interaction

Plants are constantly exposed to microbes, for this reason they have evolved sophisticated strategies to perceive and identify biotic interactions. Thus, plants have large collections of so-called resistance (R) proteins that recognize specific microbe factors as signals of invasion. One of these proteins is codified by the Arabidopsis thaliana HR4 gene in the Col-0 ecotype that is homologous to RPW8 genes present in the Ms-0 ecotype. In this study, we investigated the expression patterns of the HR4 gene in Arabidopsis seedlings interacting with the beneficial fungus Trichoderma atroviride. We observed the induction of the HR4 gene mainly at 96 hpi when the fungus interaction was established. Furthermore, we found that the HR4 gene was differentially regulated in interactions with the beneficial bacterium Pseudomonas fluorescens and the pathogenic bacterium P. syringae. When hormone treatments were applied to A. thaliana (Col-0), each hormone treatment induced changes in HR4 gene expression. On the other hand, the expression of the RPW8.1 and RPW8.2 genes of Arabidopsis ecotype Ms-0 in interaction with T. atroviride was assessed. Interestingly, these genes are interaction-responsive; in particular, the RPW8.1 gene shows a very high level of expression in the later stages of interaction. These results indicate that HR4 and RPW8 genes could play a role in the establishment of Arabidopsis interactions with beneficial microbes.

[Temporal diversity dynamics of the arbuscular mycorrhizal fungi of Larrea tridentata (Sesse & Mocino ex DC) Coville in a semi-arid ecosystem]

Arbuscular mycorrhizal fungi (AMF) of arid and semiarid ecosystems are important for the development of plants that grow under biotic stress in wild or in agro-ecosystems. There is little information on the temporal diversity of these organisms in perennial plants from arid ecosystems in northern Mexico. On this study, the mycorrhizal colonization and the temporal diversity of AMF in the rhizosphere of Larrea tridentata, perennial plant abundant in the Chihuahuan Desert region were explored. Samples of the rhizosphere and roots of fifteen plants in each of the three sampling dates during the 2015 year were obtained. A total of 17 species of HMA belonging to 12 genera and 7 families within the phylum Glomeromycota in all three sampling dates were found. Funneliformis geosporum was the dominant species belonging to the family Glomeraceae which possess the highest genera number on L. tridentata. The highest mycorrhization percentage was in February with 83.22, followed by September and May with 75.27 and 65.27%, respectively. A maximum of 16 AM fungal species were isolated and identified from L. tridentata rhizosphere in February, 15 species in May and 12 species in September. Statistical analysis showed significant differences between sampling dates in the spores number.

Bioinoculantes y concentración de la solución nutritiva sobre la producción y calidad de tomate

El objetivo del presente estudio fue evaluar dos rizobacterias promotoras del crecimiento vegetal [RPCV (Bacillus paralicheniformis y Pseudomonas lini)] inoculadas individual y co-inoculadas con dos concentraciones de solución nutritiva (SN) 75 y 100 % sobre la productividad y calidad de tomate en invernadero. Se compararon ocho tratamientos: T1= B. paralicheniformis + SN 75 %, T2= P. lini + SN 75 %, T3= co-inoculante + SN 75 %, T4= sin RPCV + SN 75 %, T5= B. paralicheniformis + SN 100 %, T6= P. lini + SN 100 %, T7= co-inoculante + SN 100 % y T8= sin RPCV + SN 100 %. El experimento se estableció en un diseño bloques al azar con 12 repeticiones. Los resultados indicaron que con el tratamiento T1 se obtuvieron los mayores valores para el rendimiento (2.09 kg/planta). El tratamiento T3 incrementó la capacidad antioxidante (46.19 µM ETrolox/100 g peso fresco) de los frutos con relación a los tratamientos sin RPCV (T4 y T8). El uso de RPCV puede ser una alternativa sostenible que permite disminuir la fertilización para mejorar la calidad sin disminuir el rendimiento de fruto, además de mitigar los efectos adversos de los fertilizantes inorgánicos en los sistemas de producción del cultivo de tomate.

The Sabinas River in Coahuila – a new hotspot of molluscan biodiversity near Cuatro Ciénegas, Chihuahuan Desert, northern Mexico

The malacofauna of the Sabinas River, Don Martin basin, Coahuila, North Mexico, was studied conchologically at nine sites. In total, 23 species of freshwater molluscs, of which 21 are native and two invasive, were found. Nineteen species are gastropods and four species bivalves. One genus and two species of subterranean (interstitial) gastropods are endemic to the area and with Lyogyrus sp. we reported for the first time a member of the family Amnicolidae in Mexico. Mexithauma quadripaludium Taylor, 1966, and Juturnia coahuilae (Taylor, 1966) (Cochliopidae), previously known only as endemics from the neighboring Cuatro Ciénegas basin, were found for the first time living out of this basin.