ORIGINAL PAPER Isolation of hydroquinone (benzene-1,4-diol) metabolite from halotolerant Bacillus methylotrophicus MHC10 and its inhibitory activity towards bacterial pathogens Venkadapathi Jeyanthi 1 • Periasamy Anbu 2 • Mariappanadar Vairamani 1 • Palaniyandi Velusamy 1 Received: 12 October 2015 / Accepted: 16 December 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract A halotolerant bacterial isolate-MHC10 with broad spectrum antibacterial activity against clinical pathogens was isolated from saltpans located in Tuticorin and Chennai (India). 16S rRNA gene analysis of MHC10 revealed close similarity to that of Bacillus methylotroph- icus. The culture conditions of B. methylotrophicus MHC10 strain were optimized for antibacterial production using different carbon and nitrogen sources, as well as varying temperature, pH, sodium chloride (NaCl) concen- trations and incubation periods. The maximum antibacte- rial activity of B. methylotrophicus MHC10 was attained when ZMB was optimized with 1 % (w/v) glucose, 0.1 % (w/v) soybean meal which corresponded to a C/N ratio of 38.83, temperature at 37 °C, pH 7.0 and 8 % NaCl. The activity remained stable between 72 and 96 h and then drastically decreased after 96 h. Solvent extraction fol- lowed by chromatographic purification steps led to the isolation of hydroquinone (benzene-1,4-diol). The structure of the purified compound was elucidated based on FTIR, 1 H NMR, and 13 C NMR spectroscopy. The compound exhibited efficient antibacterial activity against both Gram- positive and Gram-negative bacterial pathogens. The minimum inhibitory concentration (MIC) for Gram-posi- tive pathogens ranged from 15.625 to 62.5 lg/mL -1 , while it was between 7.81 and 250 lg/mL -1 for Gram-negative bacterial pathogens. This is the first report of hydroquinone produced by halotolerant B. methylotrophicus exhibiting promising antibacterial activity. Keywords Antibacterial activity  Bacillus methylotrophicus  Halotolerant  Hydroquinone  Saltpans Introduction There has been recently an upturn in the development of pathogenic microbes with antibiotic resistance, and newly emerging infectious diseases have become a major con- cern [1]. Accordingly, there is a pressing need to develop new and effective antimicrobial compounds to combat such pathogens. However, identification of natural prod- ucts from terrestrial sources has decreased owing to the rediscovery of known products [2, 3]. Furthermore, the pharmaceutical industry’s focus on natural products research has declined for the past three decades owing to a lack of compatibility with high-throughput screening (HTS) methods [4]. However, the resistance of pathogenic microbes to antibiotics indicates a need to search for novel antimicrobial compounds. Many investigators have targeted marine sources for identification of unusual metabolites. Although marine microbes are prolific, they have not been thoroughly investigated for their ability to produce novel secondary metabolites with pharmaceutical applications [5]. Moreover, a large number of biologically active compounds with antibacterial, antifungal, antidia- betic, anti-inflammatory, antiprotozoal, antituberculosis and antiviral activities have been reported from marine sources [6]. Marine Bacillus sp. comprise phylogeneti- cally and phenogenetically heterogeneous groups among & Palaniyandi Velusamy velusamy.p@ktr.srmuniv.ac.in Periasamy Anbu anbu25@yahoo.com 1 Department of Biotechnology, School of Bioengineering, SRM University, Kattankulathur 603 203, Tamil Nadu, India 2 Department of Biological Engineering, Inha University, Incheon 402-751, South Korea 123 Bioprocess Biosyst Eng DOI 10.1007/s00449-015-1526-0