Figure 1.
Biosynthesis pathways of 2-MIB in actinomycetes.
Geranyl pyrophosohate (GPP), the universal precursor of monoterpenes, is converted to 2-MIB through two steps: methylation of GPP and cyclization of methyl-GPP subsequently.
Figure 2.
GC-MS analysis of volatile compounds obtained from the gaseous phase of the Pseudanabaena sp. dqh15 culture.
Mass spectrum revealed that the main volatile compound (retenion time as 11.64 min, m/z 168) is 2-MIB.
Figure 3.
2-MIB biosynthesis associated genes identified from cyanobacterial strains.
A: Pseudanabaena sp. dqh15; B: Planktothricoides raciborskii CHAB 3331. The cnb, mtf and mic reprents cyclic nucleotide-binding protein gene, methyltransferase gene and 2-MIB cyclase gene respectively. These genes form putative operon in chromosome.
Figure 4.
Alignment of amino acid sequences of 2-MIB cyclases.
Mic-PS and Mic-PL representing proteins from Pseudanabaena sp. dqh15 and Planktothricoides raciborskii CHAB 3331 respectively; Sco7700, Sgr1269, Scab5041, Ndas2620, Caci4612, and Snas1991 represent proteins from Streptomyces coelicolor A3(2) (AL93912), S. griseus NBRC 13350 (AP009493), S. scabiei 87.22 (FN554889), Nocardiopsis dassonvillei DSM 43111 (CP002040), Catenulispora acidiphila DSM 44928 (CP001700), and Stackebrandtia nassauensis DSM 44728 (CP001778), respectively. Black boxed residues show the possible Mg2+ binding sites; sites marked by * and # at the bottom indicate putative substrate binding pockets and active site lid residues respectively.
Figure 5.
Organization of genes associated with 2-MIB biosynthesis in different organisms.
The grayed, oblique-line, filled and opened arrows indicate cnb, mtf, mic and other predicted functional genes respectively.
Figure 6.
Unrooted neighbor-joining (NJ) phylogenetic trees of 2-MIB associated genes.
A: The phylogenetic tree based on putative mic genes; B: The tree based on mtf genes; C: The tree based on cnb genes. Bootstrap values (>50%) are displayed at the nodes. Accession numbers: Am. mediterranei U32 (CP002000); Ca. acidiphila DSM 44928 (CP001700); No. dassonvillei DSM 43111 (CP002040); P. fluorescens Pf0-1 (CP000094); Sa. erythraea NRRL2338 (AM420293); St. nassauensis DSM 44728 (CP001778); S. ambofaciens ATCC 23877 (AM238663); S. bingchenggensis BCW-1 (CP002047); S. coelicolor A3(2) (AL939132); S. griseus NBRC 13350 (AP009493); S. lasaliensis ATCC 31180 (AB547324); S. scabiei 87.22 (FN554889); Cyanothece sp. PCC 7424 (CP001291); Cyanothece sp. PCC 7425 (CP001344).
Figure 7.
Expression changes of 2-MIB associated genes under different light intensities.
The levels of mtf and mic expression in different light density (10 and 60 µmol photons·m−2·s−1) were calculated relative to the expression in control culture (30 µmol photons·m−2·s−1).
Figure 8.
Transcriptional changes in 2-MIB genes under darkness.
The levels of mtf and mic expression under 72 h darkness were calculated relative to the expression in control culture (light density as 30 µmol photons·m−2·s−1).