Thermophilic Bacillus strains of phylogenetic Bacillus rRNA group 5 were described as a new genus Geobacillus. Their geographical distribution included oilfields, hay compost, hydrothermal vent or soils. The members from the genus Geobacillus have a growth temperatures ranging from 35 to 78 degrees C and contained iso-branched saturated fatty acids (iso-15:0, iso-16:0 and iso-17:0) as the major fatty acids. The members of Geobacillus have similarity in their 16S rRNA gene sequences (96.5-99.2%). Thermophiles harboring intrinsically stable enzymes are suitable for industrial applications. The quest for intrinsically thermostable lipases from thermophiles is a prominent task due to the laborious processes via genetic modification.
In this paper, we report the cloning and characterization of three Paenibacillus azotofixans DNA regions containing genes involved in nitrogen fixation. Sequencing analysis revealed the presence of nifB1H1D1K1 gene organization in the 4,607-bp SacI DNA fragment. This is the first report of linkage of a nifB open reading frame upstream of the structural nif genes. The second (nifB2H2) and third (nifH3) nif homologues are confined within the 6,350-bp HindIII and 2,840-bp EcoRI DNA fragments, respectively. Phylogenetic analysis demonstrated that NifH1 and NifH2 form a monophyletic group among cyanobacterial NifH proteins. NifH3, on the other hand, clusters among NifH proteins of the highly divergent methanogenic archaea.
A thermostable extracellular lipase of Geobacillus sp. strain T1 was cloned in a prokaryotic system. Sequence analysis revealed an open reading frame of 1,251 bp in length which codes for a polypeptide of 416 amino acid residues. The polypeptide was composed of a signal peptide (28 amino acids) and a mature protein of 388 amino acids. Instead of Gly, Ala was substituted as the first residue of the conserved pentapeptide Gly-X-Ser-X-Gly. Successful gene expression was obtained with pBAD, pRSET, pET, and pGEX as under the control of araBAD, T7, T7 lac, and tac promoters, respectively. Among them, pGEX had a specific activity of 30.19 Umg(-1) which corresponds to 2927.15 Ug(-1) of wet cells after optimization. The recombinant lipase had an optimum temperature and pH of 65 degrees C and pH 9, respectively. It was stable up to 65 degrees C at pH 7 and active over a wide pH range (pH 6-11). This study presents a rapid cloning and overexpression, aimed at improving the enzyme yield for successful industrial application.