The Diversity of Endophytic Methylotrophic Bacteria in an Oil-Contaminated and an Oil-Free Mangrove Ecosystem and Their Tolerance to Heavy Metals

Methylobacterium strains were isolated from mangrove samples collected in Bertioga, SP, Brazil, from locations either contaminated or uncontaminated by oil spills. The tolerances of the strains to different heavy metals were assessed by exposing them to different concentrations of cadmium, lead, and arsenic (0.1 mM, 0.5 mM, 1 mM, 2 mM, 4 mM, and 8 mM). Additionally, the genetic diversity of Methylobacterium spp. was determined by sequence analysis of the 16S rRNA genes. The isolates from the contaminated locations were grouped, suggesting that oil can select for microorganisms that tolerate oil components and can change the methylotrophic bacterial community. Cadmium is the most toxic heavy metal assessed in this work, followed by arsenic and lead, and two isolates of Methylobacterium were found to be tolerant to all three metals. These isolates have the potential to bioremediate mangrove environments contaminated by oil spills by immobilizing the heavy metals present in the oil

Transcriptome and Secretome Analyses of Endophyte <i>Methylobacterium mesophilicum</i> and Pathogen <i>Xylella fastidiosa</i> Interacting Show Nutrient Competition

Xylella fastidiosa is the causal agent of several plant diseases affecting fruit and nut crops. Methylobacterium mesophilicum strain SR1.6/6 was isolated from Citrus sinensis and shown to promote plant growth by producing phytohormones, providing nutrients, inhibiting X. fastidiosa, and preventing Citrus Variegated Chlorosis. However, the molecular mechanisms involved in the interaction among these microbes are still unclear. The present work aimed to analyze physiological and molecular aspects of M. mesophilicum SR1.6/6 and X. fastidiosa 9a5c in co-culture. The transcriptome and secretome analyses indicated that X. fastidiosa down-regulates cell division and transport genes and up-regulates stress via induction of chaperones and pathogenicity-related genes including, the lipase-esterase LesA, a protease, as well as an oligopeptidase in response to M. mesophilicum competition. On the other hand, M. mesophilicum also down-regulated transport genes, except for iron uptake, which was up-regulated. Secretome analysis identified four proteins in M. mesophilicum exclusively produced in co-culture with X. fastidiosa, among these, three are related to phosphorous uptake. These results suggest that M. mesophilicum inhibits X. fastidiosa growth mainly due to nutrient competition for iron and phosphorous, thus promoting X. fastidiosa starvation, besides producing enzymes that degrade X. fastidiosa cell wall, mainly hydrolases. The understanding of these interactions provides a direction for control and management of the phytopathogen X. fastidiosa, and consequently, helps to improve citrus growth and productivity