Kunnen bacteriën planten redden?
Kunnen bacteriën planten redden?
De bekende ziekenhuisbacterie Pseudomonas aeruginosa maakt jaarlijks tal van mensen ziek maar wist u dat deze bacterie ook een positieve invloed kan uitoefenen op planten? De masterthesis ‘De biosynthese, regulatie en secretie van cyclische lipopeptiden in fluorescerende Pseudomonas populaties’ onthult het geheim achter de reddingsactie van de Pseudomonas bacterie.
De cocoyam plant
In Afrika, waar voedsel schaars is, wordt de knol van de cocoyam plant gebruikt als voedselbron. Nu wordt deze plant aangetast door de schimmelachtige Pythium myriotylum waardoor wortels van de plant wegrotten en opbrengsten tot 90% kunnen verminderen. Hierdoor stijgt de hongersnood en mede ook de nood aan een oplossing. Deze wordt aangeboden in de vorm van een bacterie die de groei van de schimmelachtige kan tegen gaan waardoor de plant kan floreren en monden gevoed kunnen worden.
Een bacterie met een mechanisme
De ziekenhuisbacterie Pseudomonas aeruginosa bevat een pompmechanisme waarmee antibiotica naar buiten gepompt worden. Hierdoor hebben antibiotica geen effect op de bacterie. Dit pompmechanisme is van belang om ook eigen aangemaakte stoffen naar buiten te pompen die de bacterie kunnen helpen in zijn groei of overleving. Zo maakt de Pseudomonas bacterie stoffen aan die ervoor zorgen dat de P. myriotylum niet meer kan groeien waardoor de cocoyam plant niet (verder) aangetast wordt.
Het probleem met de ziekenhuisbacterie is dat deze niet gebruikt kan worden in de grond. De bacterie zou er immers vermeerderen en er zich op de wortels van de plant hechten. Wanneer de plant opgegeten wordt, zou de mens besmet worden met de ziekenhuisbacterie. Dit is uiteraard niet gewenst. Om die reden werd er gezocht naar andere bacteriën die hetzelfde pompmechanisme bevatten maar die niet schadelijk zijn voor de mens. Pseudomonas CMR12a en CMR5c zijn hiervan voorbeelden die de wortelrot van de cocoyam plant tot de helft kunnen terugdringen. Beide bacteriën maken namelijk tal van stoffen aan die helpen de P. myriotilum te bestrijden. Eén van deze stoffen is ‘orfamide’ en werd in de thesis uitgebreid bestudeerd.
Van DNA tot orfamide
DNA is opgebouwd uit tal van genen en de aanmaak van orfamide gebeurt door de genen orfamide A, B en C. Indien deze genen niet aanwezig zijn in de bacterie, wordt er geen orfamide aangemaakt. De orfamide genen zorgen er namelijk voor dat de orfamide moleculen worden aangemaakt. Uit het onderzoek van de thesis blijkt dat deze genen echter eerst geactiveerd moeten worden door twee andere genen, namelijk luxUp en luxDown. Indien één of beide genen niet aanwezig zijn, wordt geen orfamide aangemaakt. Het belang hiervan is dat deze genen gebruikt kunnen worden om de aanmaak van orfamide te controleren.
Van binnenin naar buiten
Wanneer orfamide dan wordt aangemaakt door de bacterie is het pompmechanisme nodig om de orfamide buiten de bacterie te brengen. Dit pompmechanisme wordt eveneens aangemaakt door bepaalde genen, namelijk macA en macB. Na de activatie van de macA en macB genen, wordt het pompmechanisme aangemaakt dat ervoor zorgt dat orfamide bijna helemaal naar buiten wordt gepompt. Echter, een ander ‘helper’ pompmechanisme is nodig om orfamide helemaal naar buiten te pompen. Deze mechanismes blijken echter verschillend van bacterie tot bacterie. Pseudomonas CMR12a bevat het mechanisme NodT en OprM terwijl Pseudomonas CMR5c het mechanisme OprM en CmeC bevat. Uit het onderzoek is echter gebleken dat nog andere onbekende ‘helper’ mechanismes aanwezig zijn in de bacterie waardoor dit pompsysteem veel complexer is dan initieel gedacht. Ook heeft elk ‘helper’ mechanisme invloed op de andere mechanismes waardoor er variatie optreedt in de hoeveelheid orfamide die naar buiten wordt gepompt. Sommige pompen laten dus meer orfamide door dan anderen.
Het nut van orfamide
Om na te gaan of de Pseudomonas bacteriën een rol spelen in de bestrijding van de schimmelachtige, werden de bacteriën in de grond gebracht bij de cocoyam plant in de nabijheid van P. myriotilum. Opmerkzaam, de planten worden niet tot zeer weinig aangetast. Dit betekent dat de schimmelachtige geen tot weinig effect heeft op de plant. De bacteriën brengen dus via hun pompsysteem de eigen aangemaakte moleculen naar buiten, die helpen de schimmelachtige tegen te gaan. De vraag is nu of de molecule orfamide hierin een significante rol speelt. Uit dit onderzoek blijkt van niet. Alhoewel orfamide apart wel enige activiteit vertoont tegen de schimmelachtige, maken de Pseudomonas bacteriën vele andere stoffen aan die helpen de schimmelachtige tegen te gaan. Orfamide heeft dus een verwaarloosbaar effect wanneer de andere stoffen aanwezig zijn. Toch zou orfamide op een andere manier kunnen bijdragen aan de bescherming van de cocoyam plant. Hiervoor is echter verder onderzoek vereist.
De toekomst van de Pseudomonas
Het onderzoek naar de pompmechanismen van de Pseudomonas bacteriën is van groot belang daar ze een rol kunnen spelen in het helpen van planten. Door beter te begrijpen hoe deze mechanismen werken en waardoor ze beïnvloed worden, kunnen de bacteriën zodanig gemanipuleerd worden dat ze optimaal gebruikt worden in de landbouw. Zo kunnen deze Pseudomonas bacteriën bijdragen aan een wereld met meer voedselopbrengsten en minder hongersnood.
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