Patna, June 5 (IANS) Bihar's ruling Janata Dal-United (JD-U) Wednesday suffered a huge jolt when RJD's Prabhunath Singh won the Maharajganj Lok Sabha seat in a by-election by a whopping 137,000 votes.

Prabhunath Singh defeated P.K. Shahi of JD-U, sparking off celebrations in both the constituency and in Patna.

It was the first defeat of the JD-U in a by-election after Nitish Kumar was elected the chief minister in November 2005.

Forty-seven percent of the electorate voted Sunday in the seat, which fell  vacant after the the death of RJD MP Umashankar Singh.

The JD-U was backed by the Bharatiya Janata Party while the Lalu Prasad-led RJD had the support of the Lok Janshakti Party. The Congress fielded Jitendra Swami, who lost his security deposit.