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And  how  do  all  those  bugs  eat  the  benzene?

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And  how  do  all  those  bugs  eat  the  benzene?  

Carla  Pérez  Mon  

Benzoic  acid  is  an  organic  substance  that  can  be  found  everywhere  in  nature.  It  forms  part  of  the   proteins   of   all   living   organisms   and   it   is   very   abundant   in   plants,   where   it   contributes   to   the   construction  of  their  cell  walls.  Although  it  is  a  common  substance,  it  is  very  difficult  to  degrade;  in   other  words,  it  is  hard  to  break  it  into  its  smaller  pieces.  Only  microorganisms  have  evolved  the  ability   to  degrade  benzoic  acid  and  they  do  so  by  numerous  biological  routes  that  are  controlled  by  oxygen.  

The   degradation   of   benzoic   acid   has   been   largely   study   in   laboratories,   thus   using   single   bacteria   species  that  are  able  to  grow  outside  their  natural  medium.  However,  benzoic  acid  degradation  is   poorly  understood  in  natural  communities,  in  other  words;  is  it  not  known  what  it  would  happen  if   instead  of  having  a  single  bacterium  in  the  laboratory,  you  would  have  a  whole  group  of  different   bacteria  (bacterial  community)  growing  together  in  the  same  medium  and  forced  to  degrade  benzoic   acid.  Would  they  be  able  to  eat  the  benzoic  acid  and  hence  grow?  If  so,  how  fast  would  they  degrade   the  substance  and  how  fast  would  they  grow?  Would  it  be  a  group  of  “fast  eaters”  bacteria  which   would  be  able  to  grow  faster  and  take  over  the  community?  Would  it  make  any  difference  for  the   process   if   the   oxygen   levels   changed?   Those   are   the   main   questions   that   I   addressed   in   my   investigation.    

I   collected   water   from   a   Swedish   lake,   which   contained   the   bacterial   community   -­‐   the   group   of   different  bacteria  -­‐,  and  I  “forced”  them  to  use  benzoic  acid  by  adding  the  compound  to  the  water.  I   subdivided   the   water   with   the   BA   added   in   different   groups   (samples)   and   I   put   the   bacterial   community  within  each  of  the  groups  to  grow  under  high  amounts  of  oxygen,  low  amounts  of  oxygen   or  not  oxygen  at  all  (oxygen  conditions).  I  observed  that  the  bacterial  community  was  able  to  grow   more  under  low  amount  of  oxygen  and  that  this  translated  to  an  increase  in  the  rate  of  benzoic  acid   degradation.  I  identified  the  bacteria  groups  within  the  communities  using  genetic  tools.  I  could  not   find  any  group  of  bacteria  especially  good  in  degrading  benzoic  acid  and  thus  able  to  grow  more  than   other  members  in  the  community  for  any  of  the  oxygen  conditions.  On  contrary,  I  observed  that  the   groups  of  bacteria  and  their  proportions  were  very  different  within  the  communities,  even  for  the   samples  that  were  grown  under  the  same  oxygen  conditions.      

All  in  all,  my  results  suggest  that  many  different  bacteria  are  able  to  degrade  benzoic  acid  equally  well,   at   least   in   my   studied   bacterial   communities.   Thus,   the   breakage   of   the   substance   would   mainly   depend  on  how  many  bacteria  are  present  in  the  media  rather  than  who  is  present  there.    

     

Degree  project  in  Biology,  Master  of  Science  (2  years),  2016  

Examensarbete  i  biologi  30  hp  till  magisterexamen,  Uppsala  universitet,  2016   Biology  Education  Center  and  Dept  of  Ecology  and  Genetics  /  Limnology   Supervisors:  Martha  Schattenhofer  and  Stefan  Bertilsson  

 

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