Food Microbiology

Biography

Biography: Syed Shahzad Shah

Abstract

Our aim was to investigate bacterial growth patterns and corresponding proteomes of Lactobacillus casei GCRL 163 (a cheddar cheese isolate) when cultured in modified MRS broths without glucose and acetate as carbon sources (fermenters operated anaerobically, pH 6.5). Growth in the basal medium (peptone, yeast extract and MRS salts) was minimal but was significantly improved by addition of 0.1% Tween 80 or 0.2% triammonium citrate, with highest growth rate and extent observed for citrate plus Tween 80. Stationary-phase cells were lysed then proteins trypsin digested and analysed by nanoLC-MS/MS. Differentially expressed proteins were identified using two-sided t-test (Perseus software version 1.5.031) with a permutation-based FDR of 0.05. In the presence of Tween 80, proteins related to carbohydrate metabolism (aldehyde-alcohol dehydrogenase and glucosamine-6-phosphate deaminase), tricarboxylic acid pathway (pyruvate carboxylase subunit B) and phosphotransferases were significantly upregulated whereas lipid-related metabolism proteins were significantly depressed compared to the basal medium control or citrate-grown cells. Tween 80 plus citrate cultures showed abundant levels of lipid-related metabolism proteins and ABC-type transporter substrate-binding proteins (absent in cells grown in Tween 80 alone) that facilitated co-metabolism of substrates, producing higher growth rates. Comparison across proteomes identified the involvement of several uncharacterised proteins related to MerR transcriptional regulation of growth during starvation and involvement of autoinducer-2 kinase in sensing or phosphotransport of normally poorly-utilized substrates. These data suggest that Lb. casei GCRL 163 can use Tween 80 and citrate alone or Tween 80 in combination with citrate as a carbon source, sustaining growth in absence of sugars.