Phycology جلبک شناسی

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رفع آلودگی قارچی از محیط کشت جلبکی

با سلام

مطلب زیر در رابطه با رفع آلودگی قارچی از محیط کشت جلبکی است که بدلیل ابتلای برخی دانشجویان در زیر به آن اشاره شده است. این مطالب در ارتباطات نامه الکترونیک از پروفسور ویتون از انگلستان و پروفسور ریتچی از استرالیا دریافت و منتشر شده است:

1- It is actually, vey hard to remove fungi contamination.  You may be able to find some antibiotic which are only effecting fungi but most of them also kill cyanobacteria.  
another method is to isolate the cyanobacteria under the microscope using a tube + adding these to a sterile culture.  This is a very tiring methodologies but does work.

2- You may try using anifungal agents when during the process of media preparation.I work on Spirulina and use antibiotcis in small amount so that I can get rid of bacteria.

 Another option is introducing nitrates...It kills the rotifiers.

 

3- For unicellular cyanobacteria we've had good luck in purifying them by repeated rounds of streak plates.  We test the resulting isolated colonies for bacterial or fungal contamination by culturing sub-samples on enriched media.  However, it can take several rounds of streak plates to isolate a pure culture.

4- you may try out lactic acid and check out these pages of the Andersen book:

5- 
Try cycloeximide ( a antibiotic for eukaryotic cells). Start with 7.0 mg/liter (final concentration), in the cyanobacteria culture. First you must isolate de cyanobacteria cells, or filaments, and inoculate it in the media with cycloeximide. Good luke

 

6-  I guess I have much more a request to you than an actual answer. We had some problems with fungal contamination in certain samples, and it is indeed a bit hard to get rid of certain contaminations. I am sure that you tried some (if not all) of the following, but here are some suggestions:

- If the microorganism shows phototrophism, that may help to isolate it by illuminating at one side and expecting that the microorganism migrates;

- if the fungus is less resistant to photobleaching, a high irradiance may help isolate the cyanobacteria;

- if the cyanobacteria have air vesicles, as it happens with Spirulina, then maybe successive centrifugations collecting the supernatant could help. Maybe a little detergent would be good in order to break the surface tension.

- If the cyanobacteria have a higher settling velocity than the fungus, centrifugation would still work for enrichment. However, in any case a streaking plate cultivation should be done.

- selective media, including even antifungal agents, could be used if you are targeting some specific features of the cyanobateria (e.g. extremophiles) and depending again on the specific contamination.

- Finally, the fungus being an heterotroph, *maybe* the culture could be enriched in cyanobacteria (and depleted in fungi) if you use really low concentrations of organic carbon, either by frequent reculture, or continuous feed to a small culture flask.

 

I suppose that those fungal contaminations you observe are fast-growing, but maybe streaking-plates may still be your best shot, since it is simple, after perhaps adequate dilution and agitation (or mild sonication) of the sample in order to loose cells.

 

7- No - centrifuging will not do any good. Try 45 to 50 oC.  That kills most fungi.  BGA laugh at that. Also Chloramphenicol will kill fungi. The common fungicide called benlate sometimes works. Common bleach (sodium hypochlirite) will work but you have to wok out an appropriate concentration and dose time.  Light destoys chlorine (Cl2) so you may not have to remove it.

8-  The standard - and very simple - procedure to remove fungi is to use cyclohemiximide to kill eukaryotes. You should be able to find many references to a suitable concentration, but there is usually a huge difference in toxicity, so not particularly critical.  Cyclohexmimide is quite cheap and am sure many researchers will have some - all you need is a few mg.

 

 

 

 

 

 

 

 

 

 

 

 

  
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