Impact of glyphosate and glyphosate-based herbicides on phyllospheric Methylobacterium

Symbiotic Methylobacterium comprise a significant portion of the phyllospheric microbiome, and are known to benefit host plant growth, development, and confer tolerance to stress factors. The near ubiquitous use of the broad-spectrum herbicide, glyphosate, in farming operations globally has necessitated a more expansive evaluation of the impacts of the agent itself and formulations containing glyphosate on important components of the plant phyllosphere, including Methylobacterium.This study provides an investigation of the sensitivity of 18 strains of Methylobacterium to glyphosate and two commercially available glyphosate-based herbicides (GBH). Nearly all strains of Methylobacterium showed signs of sensitivity to the popular GBH formulations WeatherMax® and Transorb® in a modified Kirby Bauer experiment. However, exposure to pure forms of glyphosate did not show a significant effect on growth for any strain in both the Kirby Bauer test and in liquid broth, until polysorbate-20 (Tween20) was added as a surfactant. Artificially increasing membrane permeability through the introduction of polysorbate-20 caused a 78-84% reduction in bacterial cell biomass relative to controls containing glyphosate or high levels of surfactant only (0-9% and 6-37% reduction respectively). Concentrations of glyphosate as low as 0.05% w/v (500 µg/L) from both commercial formulations tested, inhibited the culturability of Methylobacterium on fresh nutrient-rich medium.To better understand the compatibility of important phyllospheric bacteria with commercial glyphosate-based herbicides, this study endeavours to characterize sensitivity in multiple strains of Methylobacterium, and explore possible mechanisms by which toxicity may be induced.

A survey of Methylobacterium species and strains reveals widespread production and varying profiles of cytokinin phytohormones

Background

Symbiotic Methylobacterium strains comprise a significant part of plant microbiomes. Their presence enhances plant productivity and stress resistance, prompting classification of these strains as plant growth-promoting bacteria (PGPB). Methylobacteria can synthesize unusually high levels of plant hormones, called cytokinins (CKs), including the most active form, trans-Zeatin (tZ).

Results

This study provides a comprehensive inventory of 46 representatives of Methylobacterium genus with respect to phytohormone production in vitro, including 16 CK forms, abscisic acid (ABA) and indole-3-acetic acid (IAA). High performance-liquid chromatography—tandem mass spectrometry (HPLC–MS/MS) analyses revealed varying abilities of Methylobacterium strains to secrete phytohormones that ranged from 5.09 to 191.47 pmol mL⁻¹ for total CKs, and 0.46 to 82.16 pmol mL⁻¹ for tZ. Results indicate that reduced methanol availability, the sole carbon source for bacteria in the medium, stimulates CK secretion by Methylobacterium. Additionally, select strains were able to transform L-tryptophan into IAA while no ABA production was detected.

Conclusions

To better understand features of CKs in plants, this study uncovers CK profiles of Methylobacterium that are instrumental in microbe selection for effective biofertilizer formulations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02454-9.

Effect of selected factors on the effectiveness ofCapsicum annuum L. anther culture

The primary aim of the study was to establish the effectiveness of induced androgenesis in in vitro anther culture of two pepper (Capsicum annuum L.) breeding lines--ATZ1 and PO, and a hybrid between these two lines (ATZ1 x PO)F1. Anther culture was maintained according to the method developed by Dumas de Vaulx et al. (1981) with some modifications. The experiment revealed that the effectiveness of androgenesis ranged from 4 %; for the ATZ1 line to 1.5 %; for the (ATZ1 x PO)F1 and strongly depended on the developmental stage of flower buds, as well as the conditions for anther culture maintenance. The development of androgenic embryos was successfully induced only in anthers which originated from the flower buds with petals equal or slightly longer than sepals and there was a clear relationship between the length of the period of anther induction on CP medium and the level of kinetin in R1 regeneration medium.