Plant-associated bacteria: survey, molecular phylogeny, genomics and recent advances

Abstract

Abstract. Bacteria that associate with plants are diverse in the habitats they occupy, their phylogeny, and their effects on plant and environmental health. The spermosphere, rhizosphere, phyllosphere, vascular tissue and endophytic regions offer distinctive habitats for bacteria. The phylogenetic diversity of bacteria in these habitats extends across the Bacterial and Archaeal Domains; however, bacteria that are known phytosymbionts or phytopathogens are classified into only four Bacterial phyla, the Cyanobacteria, Proteobacteria, Firmicutes, and Actinobacteria. Most plant-associated prokaryotes are commensals that have no detectable effect on plant growth or physiology; these are found primarily on plant surfaces. Mutualistic bacteria include the legume symbionts, Frankia, and cyanobacterial symbionts, which form nitrogen-fixing symbioses, as well as associative nitrogen-fixing bacteria and plant growth-promoting rhizobacteria, which can enhance plant growth directly by increasing nutrient availability or producing plant growth-enhancing products, and indirectly by biologically controlling plant diseases. Phytopathogenic bacteria are diverse in the symptoms they induce as well as in their invasion strategies, mechanisms of pathogenesis, culturability, and even genome structure and fluidity. Other organisms that can detrimentally influence plant health are the ice nucleating bacteria, bacteria that overproduce plant growth regulators, and the deleterious rhizobacteria, which can help control weeds. Effects of plant-associated bacteria on environmental health include contributions to the remediation of soilborne pollutants, the decomposition of organic matter, and soil aggregation. Recent advances in genomic sequencing, functional genomics, and microbial ecology are dramatically changing our research approaches to these organisms and the questions we can address about their biology and their interactions with plants.

Metaproteogenomic analysis of microbial communities in the phyllosphere and rhizosphere of rice

“…To what extent the plant may profit from microbial nitrogen fixation under these circumstances remains to be shown. It has been stated that endophytic bacteria may transfer nitrogen more efficiently to the host plant compared with rhizosphere bacteria because of their closer association with the plant (Beattie, 2006). Moreover, despite the detection of Nif proteins, care has to be taken whether nitrogen fixation is an active process in plant-associated bacteria as they may not necessarily produce an active enzyme.…”

Cytokinins - recent news and views of evolutionally old molecules

“…In most cases, it is linked to the life strategies of plant pathogens or symbionts that actively use CKs for manipulation of plant host growth and development. Diazotrophic cyanobacteria of the genus Nostoc colonise cavities in the host plant's surface developed by the plant in the absence of the cyanobiont; however, after colonisation, the cyanobacteria can rearrange the plant tissue to form differentiated, elongated host cells increasing the cyanobiont-host surface contact (Beattie 2007). This activity may involve CKs as morphogenetic tools.…”

The Effect of Fluorescent Pseudomonads Application on the Resistance of Chili Plants Against the Attack ofRalstonia SolanacearumandFusarium Oxysporumin the Field

“…The sufficient existence of fluorescent pseudomonads in rooting area is allegedly able to dissolve phosphate plays a role in repairing the plant. In accordance to Beattie (2007), one way to repair phosphorus deficiency on plant is by soil inoculation with phosphate solubilizing microorganism. Several saprophytic bacteria playing role as biological agents of wilt disease control is fluorescent pseudomonads bacteria on tomato, potato, and eggplant, and on chili (Saddler, 2005).…”