Selected Rhizosphere Bacteria Help Tomato Plants Cope with Combined Phosphorus and Salt Stresses

Plants are often challenged by multiple abiotic stresses simultaneously. The inoculation of beneficial bacteria is known to enhance plant growth under these stresses, such as phosphorus starvation or salt stress. Here, for the first time, we assessed the efficiency of selected beneficial bacterial strains in improving tomato plant growth to better cope with double stresses in salty and P-deficient soil conditions. Six strains of Arthrobacter and Bacillus with different reservoirs of plant growth-promoting traits were tested in vitro for their abilities to tolerate 2–16% (w/v) NaCl concentrations, and shown to retain their motility and phosphate-solubilizing capacity under salt stress conditions. Whether these selected bacteria promote tomato plant growth under combined P and salt stresses was investigated in greenhouse experiments. Bacterial isolates from Cameroonian soils mobilized P from different phosphate sources in shaking culture under both non-saline and saline conditions. They also enhanced plant growth in P-deficient and salt-affected soils by 47–115%, and their PGP effect was even increased in higher salt stress conditions. The results provide valuable information for prospective production of effective bio-fertilizers based on the combined application of local rock phosphate and halotolerant phosphate-solubilizing bacteria. This constitutes a promising strategy to improve plant growth in P-deficient and salt-affected soils.Peer Reviewe

Comparative Genomics Reveal a Flagellar System, a Type VI Secretion System and Plant Growth-Promoting Gene Clusters Unique to the Endophytic Bacterium Kosakonia radicincitans

The recent worldwide discovery of plant growth-promoting (PGP) Kosakonia radicincitans in a large variety of crop plants suggests that this species confers significant influence on plants, both in terms of yield increase and product quality improvement. We provide a comparative genome analysis which helps to unravel the genetic basis for K. radicincitans' motility, competitiveness and plant growth-promoting capacities. We discovered that K. radicincitans carries multiple copies of complex gene clusters, among them two flagellar systems and three type VI secretion systems (T6SSs). We speculate that host invasion may be facilitated by different flagella, and bacterial competitor suppression by effector proteins ejected via T6SSs. We found a large plasmid in K. radicincitans DSM 16656T, the species type strain, that confers the potential to exploit plant-derived carbon sources. We propose that multiple copies of complex gene clusters in K. radicincitans are metabolically expensive but provide competitive advantage over other bacterial strains in nutrient-rich environments. The comparison of the DSM 16656T genome to genomes of other genera of enteric plant growth-promoting bacteria (PGPB) exhibits traits unique to DSM 16656T and K. radicincitans, respectively, and traits shared between genera. We used the output of the in silico analysis for predicting the purpose of genomic features unique to K. radicincitans and performed microarray, PhyloChip, and microscopical analyses to gain deeper insight into the interaction of DSM 16656T, plants and associated microbiota. The comparative genome analysis will facilitate the future search for promising candidates of PGPB for sustainable crop production

Bacteria producing contractile phage tail-like particles (CPTPs) are promising alternatives to conventional pesticides

Diese Übersichtsarbeit verfolgt das Ziel, über bakterielle kontraktile Phagenderivate (englisch CPTPs) und ihr Potenzial als effiziente und Schadorganismus-spezifische Alternativen zu konventionellen chemischen Pflanzenschutzmitteln in der Land-/Forstwirtschaft und im Gartenbau zu informieren. CPTPs werden von verschiedenen Bakterien in diversen Habitaten für den interbakteriellen Konkurrenzkampf sowie zur Beeinflussung eukaryotischer Wirte, wie Pilze und Insekten, verwendet. Diese Arbeit präsentiert interessante und bemerkenswerte Beispiele für den vielfältigen Einsatz von CPTPs als leistungsfähige biologische Bekämpfungsmittel. Wir stellen die verschiedenen Typen von CPTPs vor und legen einen besonderen Fokus auf diejenigen, die eine Wirkung gegen Schadinsekten besitzen. Zusätzlich stellen wir zwei kürzlich etablierte Webservices vor, die das permanent wachsende Wissen über CPTPs mit einem Auswahlverfahren für die besten Bakterienkandidaten kombinieren, um eine zielgerichtete Anwendung der CPTPs in der nachhaltigen Pflanzenproduk­tion zu ermöglichen.This mini-review aims at raising the interest in contractile phage tail-like particles (CPTPs) of bacteria as an efficient and pest-specific alternative to conventional chemical pesticides in agriculture, horticulture and forestry. CPTPs are used by various bacteria in diverse environments for interbacterial competition or for manipulation of eukaryotic hosts, such as fungi or insects. This review gives examples for the versatile use of CPTPs as powerful biological control agents. We introduce the different types of CPTPs with a special focus on those with activity against insect plant pests. In addition, we present two currently established web services that combine the permanently increasing knowledge on CPTPs with a selection approach of the best candidate bacteria for targeted CPTP application in sustainable plant production