Rotten thallus of Red Seaweed, Gracilariopsis heteroclada Zhang et Xia, is Associated with Agar-Digesting Bacillus spp

Abstract

Agar-digesting bacteria have been hypothesized to cause rottening of the thalli of economically important marine red seaweeds, Gracilariopsis heteroclada Zhang et Xia (Gracilariaceae, Rhodophyta). However, characterization of these causative agents accompanying seaweeds' disease in the marine environment has been poorly elucidated. Thus, agar-digesting bacteria associated with 'rottening thallus' of red seaweed, were isolated and characterized. Agar-digesters were selected based on their ability to digest agar by forming a clear depression around their colony and/or liquefaction of agar. Selected agar-digesters showed a positive result for gelatinase test and arginine dihydrolase test. 16S rRNA of these isolates was successfully extracted, purified, sequenced and analyzed. Phylogenetic analyses showed that bacterial 16S rRNA sequences from rottening seaweed thalli belong to Bacillus spp (98-99%), suggesting that the isolates were significantly associated with the rottening of red seaweeds in the present investigation.