▁or ▁greater . ▁ ▁Phys ical ▁Format ▁Although ▁it ▁could ▁be ▁used ▁in ▁other ▁formats ▁( e . g ., ▁Pet ri ▁pl ates ), ▁Sim m ons ' ▁cit rate ▁ag ar ▁is ▁often ▁used ▁in ▁sl ants . ▁ ▁Inter pret ation ▁Organ isms ▁growing ▁on ▁Sim m ons ' ▁cit rate ▁ag ar ▁are ▁capable ▁of ▁using ▁cit rate ▁as ▁the ▁sole ▁carbon ▁source ▁and ▁they ▁can ▁met abol ize ▁the ▁am mon ium ▁salt ▁in ▁the ▁medium ▁( ser ving ▁as ▁a ▁sole ▁nit ro gen ▁source ▁for ▁growth ). ▁ ▁Use ▁of ▁cit rate ▁results ▁in ▁the ▁creation ▁of ▁carbon ates ▁and ▁b ic ar bon ates ▁as ▁by products . ▁Organ isms ▁de grad ing ▁cit rate ▁must ▁also ▁use ▁the ▁am mon ium ▁sal ts , ▁producing ▁am mon ia , ▁thus ▁increasing ▁the ▁p H ▁of ▁the ▁medium . ▁The ▁increase ▁in ▁p H ▁then ▁causes ▁color ▁change ▁in ▁the ▁b rom oth ym ol ▁blue ▁indicator , ▁turning ▁it ▁blue . ▁Under ▁neutral ▁conditions ▁the ▁medium ▁remains ▁a ▁green ▁color . ▁The ▁color ▁change ▁to ▁blue ▁is ▁useful ▁because ▁growth ▁on ▁Sim m ons ' ▁cit rate ▁ag ar ▁is ▁often ▁limited ▁and ▁would ▁be ▁hard ▁to ▁observe ▁if ▁it ▁were ▁not ▁for ▁the ▁color ▁change . ▁ ▁Sometimes , ▁it ▁is ▁possible ▁to ▁detect ▁growth ▁on ▁the ▁Sim m ons ' ▁cit rate ▁ag ar ▁without ▁the ▁accomp any ing ▁color ▁change ▁to ▁blue . ▁This ▁should ▁be ▁scored ▁as ▁a ▁negative ▁for