<?php

$tz = new DateTimeZone('Asia/Kolkata');
$date = new DateTime('2016-05-03 01:38:54', $tz );
#echo $date->format('Y-m-d\TH:i:s.u');
echo substr($date->format('Y-m-d\TH:i:s.u'), 0, -3) ."Z";