Functional diversity of isoprenoidal lipids in Methylobacterium extorquens PA1

Hopanoids and carotenoids are two of the major isoprenoid-derived lipid classes in prokaryotes that have been proposed to have similar membrane ordering properties as sterols. Methylobacterium extorquens contains hopanoids and carotenoids in their outer membrane, making them an ideal system to investigate whether isoprenoid lipids play a complementary role in outer membrane ordering and cellular fitness. By genetically knocking out hpnE, and crtB we disrupted the production of squalene, and phytoene in Methylobacterium extorquens PA1, which are the presumed precursors for hopanoids and carotenoids, respectively. Deletion of hpnE unexpectedly revealed that carotenoid biosynthesis utilizes squalene as a precursor resulting in a pigmentation with a C30 backbone, rather than the previously predicted C40 phytoene-derived pathway. We demonstrate that hopanoids but not carotenoids are essential for growth at high temperature. However, disruption of either carotenoid or hopanoid synthesis leads to opposing effects on outer membrane lipid packing. These observations show that hopanoids and carotenoids may serve complementary biophysical roles in the outer membrane. Phylogenetic analysis suggests that M. extorquens may have acquired the C30 pathway through lateral gene transfer with Planctomycetes. This suggests that the C30 carotenoid pathway may have provided an evolutionary advantage to M. extorquens.ImportanceAll cells have a membrane that delineates the boundary between life and its environment. To function properly, membranes must maintain a delicate balance of physical and chemical properties. Lipids play a crucial role in tuning membrane properties. In eukaryotic organisms from yeast to mammals, sterols are essential for assembling a cell surface membrane that can support life. However, bacteria generally do not make sterols, so how do they solve this problem? Hopanoids and carotenoids are two major bacterial lipids, that are proposed as sterol surrogates. In this study we explore the bacterium M. extorquens for studying the role of hopanoids and carotenoids in surface membrane properties and cellular growth. Our findings suggest that hopanoids and carotenoids may serve complementary roles balancing outer membrane properties, and provide a foundation for elucidating the principles of surface membrane adaptation.

Efecto de Methylobacterium extorquens en el desarrollo del tomate en presencia o ausencia de Fusarium oxysporum

La marchitez del tomate (Fusarium oxysporum) promueve el uso desmedido de fungicidas sintéticos, que no son económica ni ambientalmente viables. Este trabajo plantea el uso de Methylobacterium extorquens para determinar su efecto sobre el desarrollo vegetal y la vía de señalización, para la defensa de plantas de jitomate, contra fitopatógenos. A partir, de semillas de tomate var. SUN 7705 embebidas y plantas asperjadas con la bacteria a una concentración de 109 UFC mL-1, se retó a la planta con el hongo en dos ensayos. Se midieron variables de longitud de raíz en plántulas, altura de la planta, amplitud foliar, rendimiento, peso seco total de la planta y peso seco de la raíz. Se utilizó un diseño completamente al azar con seis tratamientos y cuatro repeticiones, dos plantas formaron la unidad experimental. Asimismo, se realizó un ensayo sobre la expresión de genes de defensa, en plántulas de tomate de la misma variedad. Se encontraron diferencias estadísticas significativas (p≤ 0.05) entre tratamientos embebidos y asperjados con M. extorquens y los tratamientos inoculados con F. oxysporum y los controles, reflejándose en la longitud de raíz de plántulas, altura de la planta, amplitud foliar, peso seco de la planta y de la raíz, así como en el rendimiento. Sin embargo, los genes que codifican para el grupo enzimático fenilalanina amonio liasa (PAL), proteínas (PR-6), superóxido dismutasa (SOD) y lipoxigenasa (LOX), no se expresaron significativamente en las plántulas tratadas con M. extorquens.