PHENOTYPIC CHARACTERIZATION OF INDIGENOUS SINORHIZOBIUM MELILOTI STRAINS

Simbiozni odnos između kvržičnih bakterija Sinorhizobium meliloti i lucerne (Medicago sativa L.) omogućuje značajan unos biološki vezanog dušika u tlo. U poljoprivrednoj proizvodnji prirodni proces biološke fiksacije dušika nastoji se sve više intenzivirati predsjetvenom bakterizacijom sjemena lucerne s učinkovitim sojevima S. meliloti. Bitan preduvjet za uspjeh ovog procesa je selekcija najkvalitetnijih sojeva S. meliloti koji su visoko učinkoviti i prilagođeni na određene ekološke uvjete. Cilj istraživanja je utvrditi biokemijska i ekološka svojstva autohtonih sojeva S. meliloti, odnosno utvrditi njihovu raznolikost u pogledu rasta na različitim pH vrijednostima, temperaturama, izvorima ugljikohidrata, koncentracijama soli kao i utvrditi njihovu otpornost na antibiotike. Rezultati istraživanja potvrđuju kako ispitivani sojevi S. meliloti pokazuju značajnu raznolikost u pogledu ispitivanih fenotipskih karakteristika. Pored šećera manitola svi sojevi rastu na celobiozi, manozi, melobiozi i galaktozi, a slabiji izvor ugljika za sve ispitivane sojeve su ugljikohidrati ksiloza, arabinoza, rafinoza. U jako kiselom mediju od pH 3 sojevi nisu rasli, no u blago kiseloj sredini pH 5 rasli su autohtoni sojevi Z21 i V11 te referentni soj 2011. Niti jedan ispitivani soj nije rastao na uvećanoj koncentraciji NaCl od 2 %, no sojevi V11, Os6, Os5 i Z21 su rasli napodlogama s koncentracijama NaCl od 0.5% i 1%. Ovim istraživanjem potvrđena je raznolikost ispitivanih sojeva prema sposobnosti rasta na temperaturama koje su više od optimalnih. Sojevi V11, C16 i Os4 uspješno rastu na povišenim temperaturama od 40°C, dok sojevi Os6 i Z21 nisu rasli na temperaturama od 37°C i 40°C.Symbiotic relationship between nitrogen fixing bacteria Sinorhizobium meliloti and alfalfa (Medicago sativa L.) provides a significant input of biologically fixed nitrogen in soil. Alfalfa inoculation by highly efficient S.meliloti strains to enhance naturally occurring biological nitrogen fixation has been a common agricultural practice. The most importanat key for success of pre sowing alfalfa inoculation is selection the most efficient strain that is also compatibile to different ecological conditions. The main aim of his study is to determine the biochemical and ecological characteristics of indigenous S.meliloti strains in order to reveale strains diversity according growth characteristics under different temperature conditions, pH values, salt concentration, carbon source assimilation and antibiotic resistance. The results of this study reveale considerable phenotypic diversity of all tested S.meliloti strains. Beside mannitol, all strains could grow on cellobiose, mannose, galactose, melobiose, but they were not able to utilize xylose, arabinose and raffinose as carbon source. Under strong acidic conditions (pH 3) none of the strain could grow, but at pH 5 media indigenous strains Z21 and V11 and reference strain 2011 grew well. None of tested isolates could grow on concentration of 2% NaCl, but strains V11, Os6, Os5 and Z21 could grow in medium containing 0,5% and 1% of NaCl. This study revealed that strains varied in their ability to grow at higher temperatures. The strains V11, C16 and Os4 were able to grow at a temperature 40°C, but strains Os6 and Z21 failed to grow at 37°C and 40°C