Mapnik render Error : Could not create datasource for type 'postgis'

I try to use mapnik render for a tile server. During the initialization 'renderd -f -c /usr/local/etc/renderd.conf', the following error message is displayed :

An error occurred while loading the map layer 'xxx': Could not create 
datasource for type: 'postgis'  encountered during parsing of layer
'line features' in Layer at line 19 of 'XXX/test.xml'

There is no "No plugin found for type ' postgis '" displayed.

The file XXX/test.xml is the following :

 %entities;
 ]>

Can you help me? Thanks