Mohebali Ghasemali, Ball Andrew S, Kaytash Ashk, Rasekh Behnam
Department of Petroleum Biotechnology, Biotechnology Research Center, Research Institute of Petroleum Industry, Tehran, Iran.
School of Biological Sciences, Flinders University of South Australia, Adelaide SA 5001, Australia.
Microbiology (Reading). 2008 Mar;154(Pt 3):878-885. doi: 10.1099/mic.0.2007/013011-0.
The sulfate repression of desulfurization (Dsz) phenotype represents a major barrier to the mass production of desulfurizing resting cells. This repression can be avoided by replacing sulfate with dibenzothiophene (DBT) as the main substrate for the 4S pathway. However, mass production of biocatalyst using DBT is impractical because of its high price, low water solubility, and growth inhibition by 2-hydroxybiphenyl (2-HBP), which is the end product of the 4S pathway. In this work, the results showed that readily bioavailable sulfur compounds led to repression of the desulfurization activity of Gordonia alkanivorans RIPI90A. However, the Dsz phenotype was expressed through the 4S pathway in the presence of DMSO as the sulfur source for growth. Resting cells grown on DMSO were more active than the resting cells grown on DBT. The growth rate of strain RIPI90A on DMSO was higher than when DBT was used as the sole sulfur source. DMSO concentration significantly influenced the growth pattern of the strain, and the highest growth rate was observed at a concentration of 200 microg ml(-1). Above this concentration, the growth rate gradually decreased. DBT was found to induce the Dsz phenotype, with no observed lag period, in cells grown on DMSO as the sole sulfur source. Prior to induction, the specific activity was detected as 1.4 micromol 2-HBP (g dry cell weight)(-1) h(-1), and following incubation (5 h) the highest specific activity was observed as 5.11 micromol 2-HBP (g dry cell weight)(-1 )h(-1). This study identified that resting cells can be prepared in a two-step process. First, resting cells can be produced using DMSO as the sulfur source for growth; in the second step, improvements to their desulfurizing activity can be made using DBT as an inducer. DMSO is recommended as an appropriate sulfur source for the mass production of G. alkanivorans RIPI90A.
脱硫（Dsz）表型的硫酸盐抑制是大规模生产脱硫静止细胞的主要障碍。通过用二苯并噻吩（DBT）替代硫酸盐作为4S途径的主要底物，可以避免这种抑制。然而，由于DBT价格高、水溶性低以及4S途径的终产物2-羟基联苯（2-HBP）对其生长有抑制作用，使用DBT大规模生产生物催化剂并不实际。在这项工作中，结果表明，易于生物利用的硫化合物会导致食烷戈登氏菌RIPI90A的脱硫活性受到抑制。然而，在以二甲基亚砜（DMSO）作为生长硫源的情况下，Dsz表型通过4S途径表达。在DMSO上生长的静止细胞比在DBT上生长的静止细胞更具活性。菌株RIPI90A在DMSO上的生长速率高于以DBT作为唯一硫源时。DMSO浓度显著影响菌株的生长模式，在浓度为200μg ml(-1)时观察到最高生长速率。高于此浓度，生长速率逐渐下降。发现在以DMSO作为唯一硫源生长的细胞中，DBT可诱导Dsz表型，且未观察到延迟期。诱导前，比活性检测为1.4μmol 2-HBP（g干细胞重量）(-1) h(-1)，孵育（5小时）后，观察到最高比活性为5.11μmol 2-HBP（g干细胞重量）(-1) h(-1)。本研究确定静止细胞可以通过两步法制备。首先，可以使用DMSO作为生长硫源来生产静止细胞；第二步，可以使用DBT作为诱导剂来提高其脱硫活性。推荐DMSO作为大规模生产食烷戈登氏菌RIPI90A的合适硫源。
