Malakar Pushkar, Singh Vivek K, Karmakar Richa, Venkatesh Kareenhalli V
Department of Biosciences & Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 Maharashtra India.
Department of Chemical Engineering, IIT Bombay, Mumbai, 400076 India.
Springerplus. 2014 Dec 17;3:748. doi: 10.1186/2193-1801-3-748. eCollection 2014.
Osmotic Shock is known to negatively affect growth rate along with an extended lag phase. The reduction in growth rate can be characterized as burden due to the osmotic stress. Studies have shown that production of unnecessary protein also burdens cellular growth. This has been demonstrated by growing Escherichia coli on glycerol in the presence of Isopropyl-β-D-1-thiogalactopyranoside (IPTG) to induce β-galactosidase synthesis which does not offer any benefit towards growth. The trade off between osmotic stress and burden on growth due to unnecessary gene expression has not been enumerated. The influence of osmotic stress on β-galactosidase synthesis and activity is not clearly understood. Here, we study the effect of salt concentration on β-galactosidase activity and burden on growth due to unnecessary gene expression in E.coli. We characterize the burden on growth in presence of varying concentrations of salt in the presence of IPTG using three strains, namely wild type, ∆lacI and ∆lacIlacZ mutant strains. We demonstrate that the salt concentrations, sensitively inhibits enzyme synthesis thereby influencing the burden on growth. In a wild type strain, addition of lactose into the medium demonstrated growth benefit at low salt concentration but not at higher concentrations. The extent of burden due to osmotic shock was higher in a lactose M9 medium than in a glycerol M9 medium. A linear relationship was observed between enzyme activity and burden on growth in various media types studied.
已知渗透休克会对生长速率产生负面影响，并伴有延长的延迟期。生长速率的降低可被视为渗透胁迫带来的负担。研究表明，不必要蛋白质的产生也会给细胞生长带来负担。这已通过在异丙基-β-D-1-硫代半乳糖苷（IPTG）存在的情况下，让大肠杆菌在甘油上生长以诱导β-半乳糖苷酶合成得到证明，而这种合成对生长并无益处。尚未对渗透胁迫与因不必要基因表达导致的生长负担之间的权衡进行阐述。渗透胁迫对β-半乳糖苷酶合成和活性的影响尚不清楚。在此，我们研究盐浓度对大肠杆菌中β-半乳糖苷酶活性以及因不必要基因表达导致的生长负担的影响。我们使用三种菌株，即野生型、∆lacI和∆lacIlacZ突变株，来表征在IPTG存在的情况下，不同盐浓度下的生长负担。我们证明，盐浓度会敏感地抑制酶的合成，从而影响生长负担。在野生型菌株中，向培养基中添加乳糖在低盐浓度下显示出对生长有益，但在高盐浓度下则不然。在乳糖M9培养基中，渗透休克导致的负担程度高于甘油M9培养基。在所研究的各种培养基类型中，观察到酶活性与生长负担之间存在线性关系。
